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LA K E CA LH O U N 1951

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CONTENTS

SUMMARY iii

INTRODUCTION

Objectives of State-Wide Pr og ra m 1Ne ed for Da ta . 1Il l inois Pr og ra m 1

Ne ed fo r This Repor t 2Scope of Inves tiga tions 2

Lake Surv ey 2Water shed Survey 2Sediment Sam ple s 2Inte rpret ation of Resu lts 2

Acknowledgment 3

RESERVOIR

Gener al Information 3Reservo ir 3Dam 4

Spillway 4Pr es en t Condi tion of Lak e - 1952 4

Methods of Surv ey 4Range Sys tem s 4Mea sur eme nt of Sediment 6

Sedimentation in the Re ser voi r 6Sum mar y of Data 6Precipita tion 6Dist ribu tion of Sedim ent 8

SEDIMENT CHARACTERISTICS

Ana lys es Made 9

Origin of Sedi ment . 9

WATERSHED

Introduction 11Soil Gr oup s 12Slopes 13Pr es en t Land Use 14Erosion 15Conservation 17

RESULTS

Cau ses of High Rate of Stor age Lo ss 18

Watershed Fac tor s 18Reservo ir Fac to rs 18

Remedial Mea sur es 18Practicabil i ty 18Rais ing the Dam 19Construction of An Additional Res erv oir 19Dredging 19Sediment Basi ns 19Vegetative Plant ings 19Watershed Trea tmen t Pr og ra m 19Cost and Benef its of Conse rvat ion 22

APPENDIX 23

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SUMMARY

1. Lake Calhoun, a rec rea ti ona l lake nearGalva , Il lin ois , was cons tr uct ed in 1924 by theLake Calhoun Associ ation . Original surf ace ar eawas 46. 1 acres and the drainage area was 13. 1square miles .

2. Detailed sedimentation surv eys were c ar

r ie d out on th e lak e in 1936 and 1947. By 1936the reservoir had lost 35. 7 percent of its originalca pa ci ty to se di me nt . By 1947 a to ta l of 73. 6

pe rcen t of or iginal capacity had been dest royedby sed iment .

3. Pr io r to 1936, sediment deposited in thelake r ep re se nt ed a loss of 1 . 88 tons per acreannually from the drai nage ar ea . After 1936 thi sincreased to 2. 14 tons per acre annually.

4. Differences in mea n annual prec ipi tat ionduring the two sedimentation periods are not great.

5. Lake Calhoun has suffered a gr ea te r an nual rate of storage depletion than has any other

re ser voi r surveyed to date in Illinois. The annu alloss has averaged 3. 21 percent 'while a rate ofless than 0. 5 percent would be desirable.

6. Dur in g hea vy ra in fal l in May 1950 thespillway failed, draining the lake. The As soc ia tion clubhouse and private cottages are now overlooking sed ime nt depos its r ath er than the lake.Recreational activities have been curtailed in thearea .

7. Chemical and physical analyses of sa mp le sof the lake sediment taken in 1936 and 1947 indicate con sid era ble velocity of wate r movementwithin the lake.

8. No appar ent change in ch ar ac te ri st ic s isevident in the sediment deposited in the lake priorto 1936 and after 1936.

9. The sediment in Lake Calhoun re pr es en tsa loss in plant food and topsoil of thousands ofdollars to the farmers in the watershed.

10. A wate rshed conservation survey showsthat there are four major soil groups in the watershed. Seve nty -th ree and two- tent hs per cen t ofthe watershed is classified as dark-co lore d, pe rmeable upland soil; 1. 7 percent as light-colored,s lowly pe rm ea bl e soil ; 20. 7 pe rc ent as l ight-co l ore d , pe rm ea bl e so i l ; and 4 . 4 pe rcen t as

bo tt om lan d.

11. Approxim ately 30 perc ent of the wa te rshed is nea rl y level to level , 32 perc ent is gent lysloping (2 to 5 perce nt), 23 perc ent is mo de ra te lysloping (5 to 10 percen t), and 15 perc ent is st ro ng lysloping (over 10 percent).

12. Of the land in cult ivat ion, 24 per cen thas no appa ren t eros ion, 44 per cent is slight tomoder atel y eroded, 20 perce nt is mod erat ely se verel y eroded, and 12 percent is seve rely eroded .Seventy-nine and four-tenths percent of the entirewatershed is in cultivation at the present time.

13. Over 50 pe rc en t of the land now in p a stu re is classified as moder ately sever ely to se

ver ely erod ed. This indic ates that thi s land has

be en farmed at one t ime and has been r e t i r e d topasture in recent y e a r s .

14. The pr es en t land use in the wat er she dindicates 79. 4 percent of the land is in cultivation, 16 perc ent in pas tu re, 1. 3 per cent in woo ds,2. 9 percent in miscel laneou s use, and 0. 4 pe rc en t

is idle.15. According to the soil conserv ation s ur

vey, 77. 5 percent of the watershed is suitable forcontinuous cultivation, 5. 8 per cen t is suita ble forlim ited cultivation, and 16. 7 per cen t is suita bleonly for pas tur e or woods. One and nin e-t ent hs

pe rcen t of the lan d no w in cu lt ivation sh ou ld beconvert ed to pas tur e or woods. This land is toosteep or eroded to cultivate safely.

16. It is es ti ma te d tha t in 1924, La ke Ca lhoun trapped about 75 percent of the sedimentrea chi ng the lake . By 1947, only 20 per cen t was

be in g trapped, the remainder passing on through

the lake and over the spillway.17. The princ ipal cause of the excessi ve r at e

of storage depletion in Lake Calhoun is due to thesmall amount of storage developed for the sizeof the drainage are a. A lake of thi s volume shou ldhave been constructed on a drainage area muchsm al le r in ar ea . This conclusi on confirms asi mi la r finding rep ort ed after the 1936 lake s ur ve y.

18. Remedial mea sur es must be consideredcarefully in this case in view of the amount of thesediment load reachi ng the lake. Abandonment ofthe lake, though not a plea sant pro spe ct, mu st beseriously considered in view of probable futuresediment damages if enlargement is not possible.The recreational advantages of the area would not

be completely dest ro yed by the ab se nc e of the lake.19. Raisi ng the pre se nt dam ten feet would

necessitate moving the clubhouse and rebuildingthe state highway which cr os se s the dam. A to ta lof 1280 ac re -f ee t would be impounded. Exp ect edsto rag e depletion would be 1. 0 to 1.5 perc en t peryear due to sedimentation if no conservation workwere done on the watershed.

20. Construction of a new dam on Fi tc h Cr ee kdownstream from the present lake has been considere d. If 832 acre- feet of water were impounded,expected storage loss would be 1. 6 to 2. 0 percent

per ye ar if no co ns er va ti on work were done on thewatershed.

21. Dredging the sedime nt fro m the lake do esnot appear economically feasible in view of thephysical f actors inv olved .

22. It is estimated that if the proposed wa te rshed treatment program outlined in this reportwere applied to the land it would reduce the sedimen t load re ac hi ng the lake by 84 per cen t. Atp re sen t , approx imate ly 80 pe rce n t of the sed iment reaching the lake passes on over the spillway; consequently, it has been est ima ted th at thewatershed treatment program alone would not have

a great effect in reducing depletion of the little

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remaining storage in the present lake.23. A sound waters hed trea tmen t pro gra m

should be ba se d on a phys ica l inven tory of theland. Thi s inve ntor y may be obtained fro m conservation survey maps such as those prepared ona portion of the watershed.

24. All cropland and past ure should be tes te dfor lim esto ne, phosphorus and potash and tr ea te d

acc ord ing to te s t . This is essent ia l to obtainproper st an ds of grasses and legu mes. La nd useadjustments should be based on a physical landinvent ory. Table 8 in this re po rt shows the ad

jus tments ne ces sa ry .25. The maj or adjus tmen ts ne ces sa ry to

plac e the pro po se d water she d program int o ef fectar e: (1) use the land according to its capab ili ties(Table 8), (2) tr ea t the soils acc ord ing to tes t,and (3) use sound rot ati ons and er os io n cont rol

p rac t ices s imi lar to those su gges ted in Tab le 9.26. The adoption of soil conser vatio n p r a c

tices means increased net income to the farmer.Illinois studies in an area comparable to the Lake

Calhoun watershed showed high-conservation farmshad net incomes of $4. 77 per acre (at 1945 prices)per ye ar more than lo w-conserva tion farms. Thisincr ease , after all costs of conservation were p aid ,amounts to $7,652 for a 160-acre farm for a 10-year period.

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THE SILTING OF LAKE CALHOUN

Galva, Illinois

J. B. Stall, As si st an t Engi neer , Illi nois State Water Survey Division,

Urbana, I l l inois .

A. A. Klingebiel, State Soil Scient ist, Soil Conser vatio n Ser vic e, Urb ana ,Illinois.

E. L. Sauer, Res ear ch Proj ect Supervi sor, Soil Conservation Serviceand Illinois Agric ultur al Experi ment Station Cooperating, Urba na,Illinois.

S. W. Melsted, Associate Prof essor of Soil Analysis, Resear ch, Agro nomyDepartm ent, College of Agricu lture and Agric ultu ral Expe rime ntStation, Uni versi ty of Illi nois, U rbana, Illi nois.

INTRODUCTION

OBJECTIVES OF STATE-WIDE PROGRAM

Need fo r Da ta . Many people be lie ve tha t thecontinuation of present methods of American agriculture will lead our country into an agriculturaldepression similar to that of the barren wastes ofChina and Asia Minor. The fer til e topso il is b eing stripp ed from its res ting place and depos ited atthe bottom of st re am s and lak es. This mov eme nt

of soil ruins the thousands of years of Nature'swork in forming the productive topsoil.

The menace of sedim entat ion, which dep let esthe capacity of a re se rv oi r, is not gener ally wellunderstood. That soil erosion takes place in ev er y

par t of I ll inois is evidenced by the turbid waterfound in st re am s, espe cial ly after heavy rai ns.Whenever a dam is built to impound the water ofa stream , it immediately begins to stor e the tur bid water and the sediment begins to se tt le out.This de cr ea se s the cap aci ty of the impoundingres erv oir . The destruction of the s torage r es ervoir begins immediately upon its completion.

A study of the State of Illinois has been made

1

which shows that th er e are only appr oxim atel y1100 sites within the boundaries of the state onwhich reservoirs could economically be located.About 500 of these reservoirs have been construc ted to date. Consequently, the developmentof the remaining one half of the state's reservoirsmust be carried out only with a clear understanding of the forces which tend to destroy as well asto elongate the life of a reservoir.

Residents in the vicinity of a lake may noticethat it beco mes muddy after a rain, but the wa te rquickly clears up again and the public is not reminded that the silt load of the water has settledout and now rests on the bottom of the lake whereit occ upi es space or igi nall y designed to s torewat er . Na tu re 's gifts ar e the bas is of all life.It is our duty to halt this waste of natural resourcesnowbefore it is too late.

Il l inois Pro gra m. The seri ousn ess of er osion in Illinois and the consequent rapid reservoirsedimentation led the Illinois State Water SurveyDivis i on, the Il l inoi s Agr icu ltu re Exper imen tStation, and the Soil Conserv ation Ser vic e, in 1936to join in a cooperative study to determine theeffects of different re se rv oi r, wate rshed , andclimatic factors on the rate of sedimentation ofres erv oir s. Up to the present time, sediment ationdata in some form are available on 41 reservoirswithin the s ta t e . Eighteen of these re se rv oi rshave been subjected to detailed sedimentationsur vey s. By thi s method it is possib le to de te rmine accurately the original and present volumeof the re se rv oi r, as well as the rate of stor ageloss per year . In four case s it has been poss ibl eto resurvey a reservoir after an elapsed periodof ten ye ar s to det er mi ne the change in rat e ofsedimentation where this occurs-.

The s ta te-wide program has been orientedtoward determining sediment production indicesin those areas of the state in which further reservoir development for water supply is likely to

be g r e a t e s t . App r ox im at e l y t wo - t h i r d s of theState of Illinois depends predominately on surfacewater reservoirs as a means of public water sup

ply. Within this a rea there a re 110 communities

1. Prel imin ary Data on Surface Water Reso urce s. StateWater Survey Division Bulletin No. 3 1, 157 pp ., Urbana, Ill i

nois, 1937.

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which now exceed 1, 000 in popula tion, and pr ob ably within the next few decades will be in needof an incr ease d public water supply. The na tu ra l

boundar ies of so i ls an d physiography wi th in thi sportion of th e state ha ve de termined th e specificstudy areas in which sedimentation work will beconcentrated. 2

The specific objectives of the state-wide program as well as the study reported herein are:

(1) to establish information on factors affectingsedimentation; (2) to furnish factual data for futu re res er vo ir development; (3) to provi de datafor estimating sedimentation damages to existingand proposed reservoirs; and (4) to develop methods of sedimentation control.

Ne ed tor This Report . The lak e an d wa te r shed sur ve ys and this re po rt on Lake Calhounconstitute a part of the state-wide pr ogr am. Thisreservoir is representative of one having a smallwatershed and a very low capacity-watershed ratio.The wat er sh ed as a whole is ch ara ct er iz ed by

ma tu re topogra phy, which was developed on thegently undulatory surface of the glacial till plain.The drainage pattern is typically dendritic and thewater shed is roughly fan-shaped. Near the nor thedge of the watershed several points on the uplandin Stark County approach an elevation of 850 feetabove sea leve l, or 135 feet above c re st le ve l ofthe la ke. The tr ib ut ar y vall eys ar e short butnum ero us and a r e V-shaped in c ros s -se c t i on .Only Fitch Creek has developed a true valley flatfrom which the valley walls rise steeply 50 to 60feet to the level of the upland.

SCOPE OF INVESTIGATIONS

Lake Survey. A detailed sur vey of Lak e Cal houn was made by the Central Reservoir Party,Section of Sediment ation Stud ies, Divisi on of Re search of the Soil Conservation Service betweenJul y 23 and August 6, 1936, under s upe rv is io n ofL. M. Glymph, J r . , Chief of Pa rt y. In thi s su rvey the original and the then 1936 shoreline of thelake were mapped and a series of ten silt rangeswas est abl ish ed on the lake . By thi s me an s theor ig in al and the 1936 capa cit y of the lake weredetermined as well as the volume of sediment de

posited in th e lak e since i ts const ruct ion. P e r manent monuments, consisting of iron pipe stampedwith identifying station numbers and set in concre te, wer e used to ma rk all stations and rangeends.

A resurvey of Lake Calhoun was made fromJuly 21- 25 , 1947 by a field pa rt y of the Illin oisState Water Survey Division. In makin g the re -

survey it was necessary to remap completely theshor elin e beca use the spil lway cr es t had beenra is ed since the 1936 surve y. As a re su lt of therise in the water level many of the original surveystations were subm erge d or washed out. In th es ecases the stations were re-establ ished or al te rn at estations were located above the present crest line.Soundings along eight of the original ranges acrossthe main body of the lake were measured and new

cr os s- se ct io ns wer e obtained. Since the 1936cross-sections of the lake showed the original soil

profile and the sed iment th ickness in 1936 , thelatter was not remeasured but soundings weretaken across the ranges to locate the 1947 top ofthe sediment. By this means the pres ent capaci tyof the lake, the total volume of sediment depo sit edin the lake since its cons truc tio n, and the amou ntof sediment that had accumulated since the 1936surv ey, wer e det erm ine d. Since the spil lwaycr est has been ra is ed, los s in capacity has beencomputed on the basis of the original as well asthe new capacity of the reservoir.

Wat ersh ed Surve y. As a pa rt of thi s study adetailed soil conservation survey of portions ofthe drainage area was carried out by the Soil Conserva tion Servi ce. Kind of soil, stee pnes s of sl opeand degree of erosion were mapped to determine,if possible, the areas which contribute most heavilyto the sediment reac hing the lake. This in fo rm ation also allows recommendations to be made regarding the capabilities of the land for agriculturaluse.

A study has been made of the history of theland use in the drainage area during the life ofthe lake. This was ca rr ie d out by Soil Co ns er

vation Serv ice and the Illinois Agri cul tur al Ex-. periment Station to learn of any significant changes

in the land use trends during the life of the lakewhich might affect sedimentation in the lake.

Sediment Sampl es. During the course of the1936 survey a series of eleven sediment sampleswas taken from various parts of the lake by meansof a special samp ler. The locations of the se s a m

pl es a re shown in Fi gu re 3. In 1947 anot her s e r i e sof nine sediment samples was taken from the lake.The chemical and physical analyses of all thesesamples were made by the Illinois Agricultural

Expe rim ent Station. Thes e anal yses re po rt thete xt ur e , coll oida l content, volume-weight andp re s en ce of plant food const i tuents in the sed i me nt of the la ke . Th es e data give significantindicat ions as to the wate rs hed sou rce s of thesed iment in the re se r vo i r . A compari son has

be en made of the s a m p l e s obtained in 1936 an d1947.

Inter pretat ion of Resu lts . The final int erpreta tion of the si l ting prob lem at Lak e Ca lho unhas been made on the basis of the complete reservoir and watershed data by the three cooperating

agencies. Results are prese nted so as to be mo st

2. Illinois Sedimentation Pro gr am . Unpublished me mo rand um, 8 pp ., State Water Survey , August 30, 1949.

3. Glymph , L. M. and Jon es, V. H., Adv ance Rep orton the Sedimenta tion Survey of Lake Calhoun, G alva , Illi noi s.

SCS-SS-16, Washington, D. C., May 1937.

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helpful to res erv oir owners. The rate of dep osi t ion of sediment in the reservoir is very greatand therefore remedial measures are discussedto reduce this rate by the application of a compl ete wa te rsh ed protect ive p r o gr a m.

ACKNOWLEDGMENT

The Lake Calhoun Ass oci ati on, Inc. The

agenc ies conducting thi s su rve y wis h to ack now ledge the generous assistance and cooperation ofthe Lak e Calhoun Ass oci at io n, I nc. In the 1936survey John Lovgren , Sec re ta ry of the Lake C al houn Association assisted by making boats available to the survey party and by furnishing concreteand pipe for the sur vey mon ume nt s. Mr . Le onBest, Secr etar y of the Association, and Mr. Ing le,car eta ker at the lake, provided boats for the 1947survey.

State Water Survey Division. The re su rv eyof Lake Calhoun was made by a field party of the

Engineering Subdivision consisting of the following men: Ber nt O. La rs on, Chief of Par ty , JohnB. Stall, As sis tan t Engi neer , and Lesl ie Jonesand Douglas Rucker, Engineering Ass ist ant s. Th isdivision mad e the computations on the re su lt s ofthe lake res ur vey , including the water and se di ment vol ume s. The engineer ing section of thisrepor t was prep are d by Mr. Stall. The ent ir e r e

port wa s co mp ile d by Mr. Stal l un de r the s up er vis ion of Mr . H. E. Hudson, J r . , Head of theEngin eering Subdivision. Some photo graphs use din the report were taken by personnel of this division.

Soil Conservati on Serv ice. The Soil Co ns er vation Service of the United States Department ofAgri cult ure has part ici pat d in the Illinois sedi mentati on pr og ra m in many ways. The ori gina lsurvey of Lake Calhoun was made by the CentralReser voir Part y, Section of Sedimentation Stu di es,Division of Re se ar ch , from July 23 to August 6,1936. The field pe rs on ne l cons ist ed of L. M.Glymph, J r . , Chief of Par ty, V. H. Jones, A ss is t ant Chief, W. G. Shannon, H. L. F is ch er , andD. D. Pr ic e . The original survey res ult s andcomputations of water and sediment volumes weremade by the Soil Conservation Service and a re

por t on the sedimentat ion survey wa s p re pa redby Lo ui s M. Glymph, Jr . an d Vi ct or H. J o n e s . 3

The Sedimentation Section of the Office of Research in Washington furnished the specializedfield equipment for the re sur ve y work. Mr. L. C.

Gott schal k, Head of the Sedimentati on Section,gave technical assistance during two weeks spentwith the survey party at the beginning of the summ e r ' s wor k in 1947, and rev iew ed the pr ese ntr e p o r t .

Mr . B. B. Cl ark , State Conser vation is t ,cooperated by authorizing the soil conservationsurvey of this watershed by Soil ConservationService personnel and cooperated with the authorsin the compilation of thi s repo rt . The field workof the watershed survey was carried out by Mr.La wr enc e Benso n, Soil Scien tist , duri ng 1947.Mr . A. A. Klingebiel, State Soil Sci ent ist , a na lyzed the survey data and prepared the watershedsectio n of the rep ort . H. M. Smi th, Soil Scie nti st, assi ste d with the pre par ati on of the detai ledconservation program needed on the watershed.

Illinois Agricult ural Experi ment Station. Inthe 1936 surv ey the Soil Con ser vat ion Servicefield party obtained eleven sediment samples fromthe rese rv oi r with the cooperation of Dr. E. E.DeTurk and Dr. R. N. Br ay of the Division of SoilAnal ysis. The field par ty of the State Wat er Sur vey obtained another set of nine sediment sampl es in 1947. Under the su per visi on of Dr. E. E.DeTurk, Professor of Soil Fertility, these sampleswer e analyzed in detail in the l abo rat ory of theAgricu ltura l Experim ent Station. The in te rp re tation of these analyses and their comparison towa te rs he d soil s has been ca rr ie d out by S. W.Melsted , A ssoc iate Prof ess or of Soil Anal ysis.Dr. Melsted also compiled the section of thi s r e

port inter pr et ing th e ana lyt ical resu l ts .

Dr. E. L. Sauer , Res ear ch Pro jec t Superviso r, Soil Conservation Service and Illinois A gr i cultural Experime nt Station cooperatin g, ca rr ie d

out the study of land use and conservation historyof the wat ers hed . This study entail ed both fieldvisits and study of public records and their inter

preta t ion . Dr . Sauer a l so p r e p a r ed the da ta inthis re po rt concerning the costs and benefits ofconservation.

Knox County Soil Cons erva tio n Dis tr ic t. Inthe conduct of the agricultural phases of this studythe Knox County Soil Conservation District cooperated by authorizing the use of federal personnel assigned to the district to carry out theconservat ion survey of the draina ge area.

The Illinois State Soil Conservation DistrictsBoard cooperated in this study by financing thelaboratory work in making the sediment analysis.This work was carried out in the laboratories ofthe Illinois Agricultural Experiment Station.

RESERVOIR

GENERAL INFORMATION

Rese rvoi r. Lake Calhoun is located five mi lessoutheast of the city of Galva in Sections 14 and

23 of T. 13 N. , R. 4 E. in Knox County, as shownin Fi gu re 1. The lake was impou nded on Fit chCre ek, a sma ll st re am flowing gen era ll y southward into Walnut Creek and thence into Spoon

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FIG. 1. LAKE CALHOUN LOCATION.

Riv er, a pa rt of the Illinoi s Rive r sys te m. Thevalley has steep sides and a well-developed flood

pl ai n of approx imately 600 fe et in width. At the

p r e s e n t spi l lway c r e s t elevation of 71 8. 64 fe etM. S. L . , the lake has an ave rag e width of 700 feetand extends approximately 3,000 feet from thedam in a nor the as t e r l y d i rec t ion . A t r ibu t a rya r m of th e la ke , abo ut 1, 000 feet long and 300feet wide at its lo wer end, join s the wes t side ofthe main basin approximately 800 feet above thedam.

The lake was completed and storage startedin Sep tem ber 1924. This is enti rel y a r ec re ational lake and is owned by the Lake Calhoun Association, Inc. No wat er is pumped from the lake.

Dam. The dam consis ts of an ear th fill witha puddled cor e reinf orce d by a boa rd wall. Thedam is 735 feet long, including the s pill way at th ewest end, and has a 24-foot cr es t which ac co mmo da te s the pavem ent and guar d ra il s of StateHighw ay No. 17. The to p of the dam is at el evation approximately 728 feet above mean sealev el. The slop es of the up st re am and downst re am fac es ar e 3 to 1 and 2 1/2 to 1, re sp ec tively.

Spillway. The con cre te spill way is loca tedat the ex tr em e west end of the dam , and ha s anov er -a ll length of 48 feet . When construct ed,

this spillway had an effective crest length of 20feet, overflow passi ng through four rec tangu larnot che s 5 feet wide and 2 1/2 fee t dee p. The ef

fective crest elevation at the bottom of the notcheswas then 715 .75 feet above me an sea leve l. In1946 oak planking was added to the rectangularwe ir s, thereby raising the effective spillway cr es tto an elevation of 718. 64 feet above mean seale v e l .

The outfall channel of the spillway originallyconsis ted of a five-s tep concrete apron energyd i s s ip a to r .

Pr es en t Condition of Lake - 1952. Duringheavy rai ns in May 1950, the spi llw ay fail ed andwas washed out completely. Since that date the re

has been no water sto rage in the lake at al l. Thesediment deposits are exposed to the drying effectsof wind and sun; vegetation has sprung up on thesediment depos its. Pr es en t condition of the lakeis shown in Figure 2.

METHODS OF SURVEY

Range Syst ems. The re cor d of sedi ment ati onin Lake Calhoun is based on the survey systemes ta bl is he d in 1936 by the field pa rt y of th e U. S.Soil Conservation Service under the direction ofLoui s M. Glymph, J r . , Chief of Pa rt y. At that

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F IG. 2 . VIEW OF EX P OS ED S EDIME NT DEP OS ITS

IN LAKE CALHOUN.

time a detailed sedimentation survey of the reservoir was made cooperatively by the same threeagenci es conducting the pre sen t studi es. A tr i -angulation net of 10 stations was expanded froma 600-foot baseline chained across the dam; thisserved as control for the mapping of the shoreline and the es ta bl is hm en t of the s ys te m of tensilt rang es on the lake. Range ends and tr ia ng u-lation stations were marked with iron pipe set in

concrete and stamped with station num ber s. Ma pping was done with pl an e ta bl e an d telescopic a l i dade to a scale of one inch equals 100 feet. F i g ure 3 is a base map of the lake showing the surveynetwork.

All values of storage capacity and silt volumesfor the reservoir were determined by the rangemethod of survey developed by the Soil Conservation Service and described in their Bulletin No.524, "Sil t ing of Re se rv oi rs ." 4

4. Eakin, H. M., S il t ing of Re se rv oi rs , U. S . Dept. of

Agr i cu l t u re Techn ica l Bu l le t in 524, Re v ised by C. B. Bro wn ,

168 pp . , i l lu s t ra ted . W ash ington , U. S . Governmen t P r i n t i ng

Office, 1939.

FIG. 3.

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Mea sur eme nt of Sedimen t. In 1936 sou ndingsof water depth were taken at intervals of 25 feetalong each sediment range to locate the elevationof the top of the sediment at tha t ti me . Soundi ngswere taken with a bell-shaped 6-pound aluminumsounding weight with a base diameter of 5 inchesand a heigh t of 6 inc hes . At in te rv al s of 50 feetor with alt ern ate soundings, the thi cknes s of thesilt was me as ur ed with a "spud " bar. This is a

specially designed instrument developed for thiswork by the Soil Conserva tion Ser vic e. As shownin Figure 4 this consists of a steel rod made upof cup-shaped grooves every one-tenth of a foot.On the range line this spud is thrown spearlikeinto the sediment on the end of a calibrated line.It passes through the soft sediment and penetratesthe original soil or pr e- re se rv oi r deposit. Theb a r i s then r e t r i e v e d an d in the boat the actualthickness of the sediment is measured by inspecting the small soil or sediment samples retainedin the cups.

FI G. 4. USE OF SPUD IN MEASURIN G SEDIMEN TTHICKNESS.

In 1947 a detailed resurvey of this reservoirwas carried out by a field crew of the State WaterSurvey Division under Ber nt O. La rs on , Chief ofPar ty. In making the resu rvey it was ne ces sa ryto rem ap compl etel y the shore lin e beca use the

spillway crest had been raised since the 1936sur vey . As a re sul t of this ri se in wat er leve l,many of the ori ginal surve y stations were su bmer ged or washed out. In such case s the sta ti onswere re-es tablished or a lternate s ta tions werelocated above the pre sen t cr es t line. Since the1936 cross-sections of this lake showed the originalsoil profile and the sediment thickness in 1936,thes e ran ges were not re- spud ded but were r esound ed to locat e the 1947 top of the s edi men t.A to tal of 98 mea su re me nt s were made on theeight ra ng es shown in Fi gu re 3. On Rang e 014-015, which had not been prev ious ly surv eye d, thespud was used to me as ur e sed ime nt thi ckn ess.

Measurements were made at 50-feet intervalsexcept on the above-mentioned range on which25-foot intervals were taken.

SEDIMENTATION IN THE RESERVOIR

Summ ary of Data. Table 1 is a su mm ar y ofthe sedimentation data obtained from the two sur

veys of Lake Calhoun, toge ther with data deri ve dtherefrom which are pertinent to the sedimentationproblem in th e lake. Sinc e the sp illway ha d no tbe en ra i s ed at the t im e of the 1936 survey, th eresults of that survey have been converted to the1947 elevation so that the results of the two surveys will be comp arab le. All re sul ts in Table 1are based on the 1947 spillway crest elevation.Significant findings shown in this summary are:

1. The capacity of the res er vo ir for wat erstorage has been reduced by 73. 6 percent sinceits construc tion, a perio d of just 22. 9 year s.

2. The sedim ent accumu lati on in the lakerepresents an average annual soil loss of 71.41cubic feet of soil per acre per year from the watershed.

It is interesting to note that the volume ofsediment in the re ser vo ir in 1947 is gre ate r thanthe original capacity of the re se rv oi r before thedam was ra is ed . Thi s ra te of sediment acion isobviously exc ess ive . An explanat ion of thi s highrate of sedimentation can be found by observingthe relatively low capacity-watershed ratio (C/Wratio) of the lake . The ori gin al C/W ra ti o of theres erv oir was 21.8 acre- fee t per square mile .In other word s, the res er vo ir was designed andconstructed to furnish about 21.8 a cre- fee t of st or

age space for every squa re mile of wat ersh ed.Sedimentation studies in Illinois and in other partsof the country5 have shown that the original C/Wratio of a reservoir is significant in determiningthe rate at which the reservoir will collect sediment. A small capacity res erv oir which re cei ve ssediment from a large watershed area will losecapacity much faster than a high-capacity reserv oir with a sma ll wate rshe d. The C/W rati oof 21.8 acr e- fee t per squar e mil e for Lake Cal houn is undoubtedly one of the principal factorswhich explain the rapid rate at which Lake Calhounis losing capacity.

Preci pita tion. Table 1 shows that from 1924to 1936 the annual sediment deposited in the lakeamounted to 1. 88 tons per acre from the drainagearea while during 1936 to 1947 this annual averagehad in cr ea sed to 2. 14 tons per acr e. This increase in sediment production may have beencaused by any of se ve ra l fa ct or s, including differ enc es in inte nsit y, dura tion , and frequencyof pre cip it ati on duri ng the two pe ri od s. U. S.

5. Brown, C. B . , The Contro l of Res erv oi r Silting,U.S. D. A. Soil Conse rvati on Servi ce Misc. Public ation No.521, Washington, D. C., 1944.

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Table 1

Summary of Sedimentation Data on Lake CalhounGalva, Illinois

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Weather Bur eau rec ord s at Galva, Illinois, showthat during the ear li er period (1924-1936) mea nannual prec ipit ati on was 31. 72 inches, while du ring the latter period (1936-1947) the mean was32. 33 in ch es . The lo ng- te rm annual mean is32. 02 inche s. Since mean avera ge preci pitat iondoes not provide information on the intensity ,durati on, and frequency of pre cipi tat ion , it is oflittle value in explaining the increased sediment

produc tion . Increased sediment production ma y

also be due to increased intensity of land cultivation in recent years.

Distri bution of Sediment. The hea vie st de po sition has occurred in the upper part of the lake.Pe rc en t los s of capaci ty in the nine segmentsrange from 87 percent in the headwaters at theextreme northeast end of the lake to 54 percentloss of stor age near the dam. Figu re 5 veri fie sthis and also shows that there would be very littlewater in the upper section of the lake had not theelevati on of the spillway been ra is ed . In no se gment does there remain more than 46 percent ofthe original stora ge capacity. Fig ure 5 shows the

cross-sections of water and sediment along ranges01-02 and 011-010 located as shown in Figure 3.

In Table 2 the sedimentation in Lake Calhounis tabulated in comparison to similar results onfour other re se rv oi r s in Illi nois. The effect ofthe capacity-watershed ratio on the storage lossis exemplified by comparing Lake Calhoun to LakeBracken, near Galesburg. The original capa city -watershed ratio of Lake Bracken was nearly tenti me s as gr ea t as Lake Calhoun. Also, LakeBracken has lost an average of only 0. 58 percent

of original capacity each ye ar , while Lake Calhounhas suffered a los s of 3. 21 per cen t pe r year .

Carthage res er vo ir was construc ted with anoriginal stora ge capacity of 406 acr e- fee t. Thislake receives the drainage from 2. 94 square miles.Lake Calhoun, howev er, with a comp arab le or iginal storage volume of 424. 7 acr e-f eet , was constructed to receive the drainage from 13.0 squaremi le s. The ra te s of sediment production ar e notgreatly different2.47 tons per acre per year atCarthage and 2. 00 tons per acre per year at LakeCalhoun. However, per cent age- wis e, the sed imentation in these two cases is greatly different;the Carthage reservoir has lost only 1. 03 percent

per ye ar while Lake Calhoun ha s los t 3. 21 percen teach year.

F IG. 5 . TYP ICA L S EDI MENT CROS S S ECTIO NS , LAKE CALHOUN.

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Table 2

SEDIMENTATION OF LAKE CALHOUN COMPARED

TO OTHER ILLINOIS RESERVOIRS

SEDIMENT CHARACTERISTICS

Analy ses Made. The chem ical and phys icalcharacteristics of the Lake Calhoun sediment weredetermined by analysis of sediment samples takenfrom rep res ent ati ve locations within the lak e, asshown in Figure 3. These sediment sam ple s we reanalyzed for total nitroge n, total organi c carb on,

pH, available potass ium, available phosphorus,and volume-w eight. Two sa mp les , nu mber 4 and6, wer e analyzed for base-exch ange c ha rac ter is t ic s and par t icl e size distr ibu tion. The data

are given in Table 3.The sediments appear to be quite uniform in

their chemical and physical cha ract eris tic s. Thetotal nitrogen values vary only from 0. 13 to 0. 24per cen t, and the to ta l organi c ca rb on va lue s rangefrom 1. 47 to 2. 77 per cen t. Sim ila rly , val ues forvolume-weight vary only from a low of 0. 703 toa high of 1. 09. This uniform ity sug ges ts considerable water movement within the lake and

probably a uni for mit y in depth of sediment depositi on. While sa mp le s 4, 5, 7, and 9 ar e uni formly low in volume-weight and high in organiccarb on, and sa mp le s num ber 1, 2, 3, 6, and 8

are higher in volume-weight and lower in organiccarbon, these differences are not as gre at as onewould expect from the relative locations of thesesam ple s in the lake. Howe ver, some sor tin g ofsed ime nt ha s oc cu rr ed within the lake with thefiner deposits nearest to the dam.

Origin of Sedim ent. The unifo rmity of te xture and chemical characteristics of the sedimentsindicate that the origin of the sediments must be

largely loess and loess-derived soi ls .A comparison of the chemical characteristics

of the sediment samples taken in 1947 with thoseof samples taken in 1936 (Table 4) reveals thatno apparent change has occurred in the nature ofthe sed ime nts depo sited durin g this per iod. In1936, a s now, the sediment ma te ri al s were quiteuniform. This lack of change in the na tu re of thesediments would seem to indicate that erosion patterns within the watershed are similar to what theywe re in 1936. Sediment control should, the re fo re ,include measures necessary to prevent erosion onthe more sloping cultivated areas of the watershed.

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Table 3

Chemical and Physical Data on 1947 Lake Calhoun Sediment Samples

T a b le 4

CHE M I CA L DAT A ON 19 36 L AKE CAL HOUN SE DI M E NT SAM PL E S

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WATERSHED

INTRODUCTION

There are a number of factors that may influence the rate of siltation in a lake or reservoir.Among thes e facto rs are the size , shape and ageof the res er vo ir , the size of the drain age ar ea ,the gener al topography and steep ness of slopes,

rainfall ch ara ct eri sti cs, the kind of soil and theland use pat ter n. The influence of eac h of th esefactors must be evaluated in a watershed wherea study is being made of the effects of these facto rs on rat e of siltation. Some of the se fact orscan be adjusted to reduce siltation in the reservoi rs , where as o thers a r e perman ent phys ica lconditions that cannot be changed.

In an effective sediment-control program fora reservoir or lake the principal sources of sediment mu st be det erm ine d. A detai led soil conservation survey map was prepared by the SoilConservation Service in the watershed. A spe cia l

study of the farming conditions was also made.The survey consisted of mapping the kind of soil,

per cent of s lope, degree of e rosion and p re se n tland use on aerial photos having a scale of 4 inchesto a mil e. Channel erosi on and amount of de po si tion were also reco rde d on the survey. A samp lesystem was used in which a 160-acre block was

mapp ed out of each section of land. The sam pl esurv ey data were extended to repre sen t 8400 a c r e s .The tota l land ar ea of the basi s is actua lly only8,320 ac re s or 13 squar e mi le s. Standard soi lconservation survey procedures were followed inthe preparation of the field maps.

The wat ers hed lies in Lynn Townshi p, KnoxCounty, Gosh en Township in Sta rk County and inGalva Tow nsh ip, Hen ry County, Illin ois. Thedra ina ge are a is 13. 0 square m ile s in size andlocated in the headwaters of Fitch Creek ( Fig ure 1).

The topography in this watershed is level togently rolling with a small percentage of strongly

Table 5

ACREAGES AND PERCENTAGES OF VARIOUS SOIL GROUPSIN LAKE CALHOUN WATERSHED

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rolling land adjacent to drainageways. The gen er alland formation consists of a thick loess coveringover wea the red glac ial drift. Only on the ver ysteepest slopes or seriously eroded spots is tillexposed on the surface.

SOIL GROUPS

Four general groups of soil may be found inthe watershed, namely (1) dark- colore d, me di um -textured, moderately permeable (Muscatine -Tama)soil group, (2) light- color ed, medi um- tex tur ed,slowly permeable (Berwick-mottled Clinton) soilgroup, (3) light-colored, med ium- text ured , mod erately permeable (Fayette-shal low Clary) soi lgro up, and (4) the bott omla nd (Huntsville) soilgro up. The ac re ag e and per cen tag e of each ofthe soil groups may be found in Table .5. F ig u re 6shows the genera l location of thes e soil group s.

The dark-c olored , medium-te xture d, moderat ely perme able soil group, Group 1, consi sts

of soi ls deri ved lar gel y from lo ess . On levelareas these soils are poorly oxidized and requiretile dra ina ge. On the sloping land the soil s ar ewell oxidized and erosion is the dominant problem.These soils are very productive and respond wellto good management.

Soil grou p 2, the l ig ht-c olor ed, med ium -textured, slowly perm eable soils are those poo rlyto imperfect ly drained soi ls that occur on theridge tops adjacent to the steeper drainageways.Some soils in this group are mapped on slopeswhich indicate a slowly permeable layer in thesubsoil. Small ar ea s of other soil groups ar e included with this group on the map shown in Figure 6. Good rot ati ons that will imp rov e the internal air-water relationship will improve thesesoils a gr ea t deal . They ar e gene ral l y low inorganic matter and respond to good management.

Soils included in group 3 are light-colored,med ium- t ex t u re d , mode r a t e ly pe rmeab le andwell drained. These soils occur along the st ee pe r

FIG. 6 . GEN ER A LIZ ED SOIL GR O UP MAP . LAKE C ALHOUN W ATE R SH ED, ILLINOIS .

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Table 6

ESTIMATED CROP YIELDS IN LAKE CALHOUN WATERSHEDON SOILS UNDER GOOD AND FAIR MANAGEMENT*

drainageways and on the nar row ridge top s. Theyrespond well to good management but are subjectto se ve re ero sio n. The se soil s ran k second intotal acreage in the watershed and comprise approximately 21 percent of the a r ea .

The bottomland soils (group 4) vary a greatdeal in th ei r potenti al use . The soils are darkin color and ar e ver y prod ucti ve; however, theyoccur along drainageways that vary in frequencyof flooding. In addition, many of the sma ll er bot toms are cut up by meandering stream channelsresulting in areas too small to cultivate.

The relative productivity of the soils in thewatershed may be found in Table 6.

SLOPES

It is generally assumed that in humid agricultural ar ea s, such as Illinois, ther e is a highcorrelation between the amount of soil washed fromthe fields in the watershed and the amount of sediment deposi ted in the re se rv oi r or lake. If this

is tr ue , then the fac tor s that influence soil los sfrom the fields should be carefully evaluated tode te rmine proper con tro l measures .

The steepness of slope is one of the mostimpo rta nt fac tor s affecting soil los s. Soil Conservation Erosion Experiment Stations6,7 through

out the country have found that as the steepnessof slope is doubled the soil loss increases two andone-half time s. Figur e 7 shows this relat ions hip.

The slopes in the watershed range from level

to over 30 per cen t. Table A in the appendi x in

dicates the distribution of slopes by soil groups.

Fig ure 8 shows the pe rc en ta ges of the various

slope groups in the watershed.

Eighty-five percent of all the level land in thewatershed occurs in soil group 1 (dark-coloredupland soi ls) . Of the soils found on gently slopi ngland ("B" s lopes), 90. 4 per cen t a r e classi fie d assoil group 1. On the mod era tel y sloping land ("C"slope s) 78. 4 pe rc en t of the so ils occur in soilgroup 1. All of the soils found on st eep er slo pes(over 18 percen t) a r e l igh t- co lore d , med ium -textur ed, mode rat ely per meab le group 3 soil s.

FIG. 7. EFF ECT OF SLOPE ON EROSION. (Bas ed onslope and practice data.)

6. Van Doren, C. A. and Gard, L. E. , Pro tecti ng YourSoil, University of Illinois in coopera tion with Soil Co nse rva tion Servi ce, Ci rcu lar N. 667, Urbana, Il linoi s, 1950.

7. Hays, O. E. and Clar k, Noble, Cropping Syste msThat Help Control Erosion, Univ ersit y of Wiscons in, Bulle tin

No. 452, Ma di so n, Wi sc on si n.

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FIG. 8. PERCENTAGE OF VARIOUS SLOPE GROUPS

IN LAKE CALHOUN WATERSHED.

PRESENT LAND USE

The pr es en t use of the land, whet her it beused for cultivated cro ps, hay, pas tur e or wood s,is another very important factor in soil lossesfrom fields and rate of sediment production inlakes and re ser voi rs . Fields cropped too st re nu ously and without regard for slope may produceover one hundred ti mes mor e soi l loss than s i mi lar land conditions in perm anent vegetation. Fi ve

different kinds of land use were classified in thewatershed, namely: (1) cropland, (2) pas tu re land,(3) woodland, (4) idle land, and (5) miscellaneous.Cropland is land on which crops were grown at thetime of the sur vey . This incl udes crops suc h ascorn, beans, small grain and rotation hay and pa s ture . Past ure land is land in perennial gr as se s,and woodland is land which has at least a 40 percent canopy of tr ee s. Miscellaneous land co ns is tsof land used for far mst eads , roa ds, et c. , whileidle land refers to those areas not used for purposes that would fu rnish an econ omic re turn. Fordetails on the distribution of present land use bythe various soil groups and slope groups refer toTable s B and C in the appendix. Fi gur e 9 indi cates the distribution of present land use in thewat ers hed. Of the 8400 ac re s in the wat ers hed ,6667 acr es ar e in cropland, 1340 ac re s in pa st ur e,108 acres in woodland, 245 acr es in misce ll ane oususe, and 40 ac re s in idle land use. Eight y-ni ne

pe rc en t of the cropla nd in the wat er sh ed wa s c l a s sified in soil group 1 (dark- colo red, per mea blesoil), whe rea s 72. 5 percen t of the pa stu re landand 73. 1 percent of the woodland was identifiedas soil group 3 (light -color ed, per mea ble soil).

Of the land in the watershed being used at thep r e s e n t as c rop land 69 . 2 pe rc e n t i s located on

slopes of les s than 5 percent slope, 30. 5 per ce nton slop es of 5 to 15 pe rc en t, and 0. 3 perc en t onslopes over 15 percent (see Table C, Appendix).Thirty-one and eight-tenths percent of the pastureland occ urs on slopes of le ss than 5 per cen t, 9. 8

pe rc en t is on slopes of fr om 5 to 15 perce nt slope,and 58. 4 percent occurs on slopes over 15 percentslope. Ninety-five per cen t of the land classi fiedas idle occurs on slopes over 15 percent in steep

n e s s .The acreage and percentage of the variousland use capability classes in Lake Calhoun watershed by present land use may be found in Table D(Appendix).

The land conditions in the watershed may beclassified into three general categories and sevenspecific cl ass es. The thr ee gene ral catego riesdivide the land into those areas suitable for regularcropping (Class I, II and III land), those suitedfor lim ite d cropp ing (Cla ss IV land ), and tho sesuited for per man ent vegetation (C las s V, VI andVII land). The seven specific cl as ses bre ak th es ethree general categories into classes of land ac

cording to the hazards involved in using the land.Table D further shows that approximately 78 percent of the watershed is suitable for regular cultivation, 6 perc ent suitable for occasi onal cul tivation and 16 percent is best suited for pasture orwoods. The percen tage of the wat ers hed now bei ngcultivated is 79. 4 percent as compared with 84

percen t that i s sui table for r egu la r an d l imi tedcultivation.

Figure 10 is a diagrammatic chart of Table D.It shows the percentage of the various land usecapability classes in the watershed as well as the

perc en ta ge of the va riou s land classes now in cul

tivation. The greates t mis use of land in the wat er shed as shown by this figure is the 14 percent ofClass VI land and 3 percent of Class VII land thatis now being cultivated. This repr ese nt s 125 a c r e s

FIG. 9 . DISTR IBUTI ON OF PR ES EN T LAND USE IN

LAKE CALHOUN W ATERS HED.

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of land in the watershed that should be in permanent pasture or woods but is now being cropped.Another major misuse of land not shown in thesetables is cropping the sloping land that is suitablefor culti vati on (Cl ass II, III and IV) too st re nu ously and without regard for the direction of slope.This is brought out in Table 8 where a suggestedwatershed treatment program is presented.

The land use history of Galva Township,Henr y County, and Lynn Towns hip, Knox Count y,in which mo st of the wat er she d li es , is shown inTable 7.

A 10- yea r aver age (1938-47) in Galva andLynn Townships indicates that 48 percent of thetillabl e land was in corn and soybeans, 21 pe rc en tin sma l l gra in, 27 per cen t in hay and pas tur e,and 4 pe rc en t mi sce ll ane ous . The intensity ofcropping is not too strenuous for Class I land;howe ver , it is too stren uou s for the sloping landin the watershed. Only 34 perc ent of the cr opl andin the watershed can stand this intensive croppingwithout conservation practices and possibly another 36 percent if careful erosion control prac

tic es ar e followed. It can be gene ral ly conclud edfrom these data that relatively large acreages inthe watershed are being cropped too intensively tocorn and soybeans.

EROSION

In developing a watershed treatment programfor protection of a lake or reservoir it is necessary to know the source of sediment and the rateof depos iti on. In ord er to analyze this probl em

FIG. 10. PER CE NT AGE OF THE VARIOUS LAND USE

CAP ABILITY CLAS S ES IN LAKE CALHOUN W ATERS HED

AND P ERCENTAGE OF EACH CLAS S IN CULTIVATION.

bo th sh ee t and gully erosion, as we ll as a r e a s ofrece nt deposition, wer e rec ord ed on the con ser vation survey map s. The following ero sio n gr ou pswere mapped:

No ap pa rent eros ion : Ap pr ox imat e originaldepth of topsoil remains.

Slight to mo de ra te eros ion : Over seveninches of the original topsoil remaining, no sub soi lexposed by the plow.

Moderately sever e erosion: Occasional tofrequen t exp osu re of subsoi l by plow, thr ee toseven inches of topsoil remaining.

Severe erosion: Erosi on of the subsoi l, le ssthan three inches of topsoil remaining.

Table 7

AVERAGE LAND USE, GALVA TOWNSHIP, HENRY COUNTY,

AND LYNN TOWNSHIP, KNOX COUNTY, ILLINOIS, 1938-47*

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Table 8

Est imated Reduction in Sheet Eros ion Annually f rom a Watershed Treatment ProgramLake Calhoun Watershed

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It is estimated from the re sul ts of the s urv eythat over 95 percent of the eroded material comesfrom sheet erosion. A pro gra m to reduce sil ta-tion in the lake would necessarily require conservation measures and practices that would greatlyreduce sheet-erosion in the watershed. Fig ure 11shows the amount of the various erosion classesin the watershed.

F I G . 1 1 . P E R C E N T A G E O F D I F F E R E N T E R O SI O N

CLASSES IN LAKE CALHOUN WATERSHED.

The percentages of the total watershed classified as moderately severe and severe erosionwere determined by measuring the amount of soileroded from the fields in the past . Thes e two e r o sion classes represent 34 percent of the acreagein the wat ers hed , or 2969 ac re s. Moderatelysev ere er osion indicat es 25 to 75 percen t of thetops oil rem ov ed and some s ubs oil being mixedwith the plow lay er, while seve re ero sio n den ote sthat 75 percent or more of the topsoil is removedand the plow lay er is la rge ly subs oil. App rox imately 61 percent of the severe erosion is foundin the num ber 3 soil group (light -col ored , welldrained soil), while 71. 3 percent of the moderatelysevere erosion occurs on the number 1 soil group(da rk- col ore d upland soi l) . For detai ls on thedistribution of the various erosion classes according to soil gro up, slope group and pr es en t landuse ref er to Tab les E, F, and G in the appe ndix .

Figure 12 indicates that a relat ively largepercen tage of the land no w in cult ivation in th e

wate rshe d i s moder a te l y sev ere ly to severe lyerod ed. Th er e is littl e doubt but that the se twoerosion class es, compris ing 32 per cen t of all thecropland in the watershe d (2149 ac re s) , ha s contributed a great deal to the rate of siltation inLak e Calho un. In addi tion to the cropl and thathas been badly eroded, over 50 pe rcen t of the landnow in pasture has less than half of the originaltops oil re mai ni ng (Table G, Appendix) . Thisprobably indicates that this e roded pas ture landwas in cultivation at one time and when it becamerelat ively unproductive through erosion i t wasconverted to pasture.

CONSERVATION

Land in the Lake Calhoun watershed has beenfarmed without due regard for the kind of soil orsteepnes s of slope. Land, like livestock, diffe rsin its abilit y to pro duc e. Some kinds of land can

be cu lt ivat ed and al lowed to remai n in cle an t i l ledcrops one-half the time while other kinds of cropland should be in hayland 50 to 75 percent of thetime . Some land needs erosion control pr ac ti ce sapplied to the cropland while others should remain in perman ent vegetation. A gre at deal of thesloping land in the watershed has been farmed asstrenuou sly as the level productive ar ea s. As aresul t, erosi on has taken its toll. The re ar e twomain factors that have been very instrumental inprod uci ng high soil los se s fr om th e fie ld s in thewat ers hed . These facto rs ar e (1) cropping thesloping land to the same degree of intensity as thelevel land, and (2) failing to use ero si on -c on tr ol

prac t ices on th e sl op in g cropland. Al th ou gh thecensus data indicate that the average percentageof cropland in clean-tilled crops in the watershed

is 48 perc en t, th er e ar e many individual fieldsand farms where corn and soybeans are grownfour ye ar s out of five. Thi s cropp ing sy st em is

practic ed on these fields i rrespective of th e slopeof the land. This pra ct i ce resu lt s in high soi llos ses . The re ar e other factors of les ser im

po rt anc e, such as failing to ma in ta in grass wa te r ways in fields and along road right-of-ways andthe overgrazing of pastures and woods.

The f ir st s tep in a sound wate rsh ed tr ea tment program is to classify the land accordingto its abilities to safely produce crops such ascorn, g rai n, hay, pas tur e and woods. Soil con servation survey maps such as those developed fora portion of the wate rsh ed, supply the ne ce ss ar yinformation needed to develop a sound land useprogram. Th es e maps should be prepared on th erema inde r of the wate rshed to supply the needed

F IG. 12 . DIS TR IBUTI ON OF TH E F OUR EROS IONCLASSES IN THE PRESENT CROPLAND IN LAKE CALHOUNW A T E R S H E D .

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bas i c land information on each fi el d and f a rm.

Soi l t es t s should be made on all crop and

pas tu r e land to de termine l imes tone , phosphate

and potash needs. These min era l element s should

be appl ied acco rding to needs in orde r to grow

good stands of legumes and grasses required in

a rotation and pasture program that will econom

ical ly control erosio n. The best level land in the

watershed should remain in grasses and legumes

at lea st one-fourth of the ti me . The sloping landsuitable for cropping should remain in grasses

and legumes a higher perce ntage of the ti me . All

sloping cropland should be farmed with the slope

and ade qua te e r os i on cont ro l pra c t i ces used .

Properly designed waterways should be established

along al l watercourses.

Many of the permanent pastures in the water-shed are eroded but may be renovated so as to

provid e g r ea t er e rosion control and yi eld l a r ge reconomic return . Pas tur e management is es se ntial along with renovation to insure the greatestfarm return. Eart h and concrete str uct ure s ma ybe needed along so me watercourses and at th e t i leoutle ts. In ord er to redu ce soil loss and al so toencou rage new growth, tim ber ar ea s should not

be grazed . Iso la ted a r e a s along dra inageways ,fence cor ne rs and sm al l s teep or eroded ar ea smight profi tably be planted to desirable shrubsor trees to provide adequate cover for wildlife.Increased wildlife population is most profitableto have in the wat ersh ed. They as si st in keepinginsects under control as well as serving recreational and aesthetic purposes.

RESULTS

CAUSES OF HIGH RATE OF STORAGE LOSS

Watershed Fac tor s. Under pres ent land usecondi tions it is e st im at ed that the mea n annualsoil loss from fields in the Lake Calhoun watershed is 8. 3 tons per ac re per yea r (Table 8). Du ring the life of the lake, how eve r, the sedimen tdeposited in the lake has averaged only 2. 0 tonsper year per acre of drainage a rea . Th is difference is caused by two things. Fi rs t, a sub stan tialamount of the soil which is eroded from the fieldmay be moved only a short distance and depositedas col luvium at the edge of a field, or as al lu vi alfans within the st re am sys tem or on the str ea mfloodplain during floods. The channels and s t r e a m smay not have gradients and capac ities to c ar ry a llof the soil broken losse from the field, all the wayinto the lake. The rem ain der is depos ited out be fore it reache s the lake. The second factor affect ing this apparent difference is the effectiveness ofthe lake in trapping the sediment which is carriedinto the lake.

Re ser voi r Fa ct or s. The tr ap eff iciency of the lake is dependent on the detention time of theinflow and the particle-size of the sediment load.A usable index to probable trap efficiency has beendevised by Brown 8 by using capacity-watershed

rati o data. By this means it is est ima ted that asoriginally constructed in 1924 at spillway elevation 715.7 5 M. S. L. and having a C/W ra ti o of 2 1. 8(see Table 1) Lake Calhoun probably trapped about70 perc ent of the incoming sedi ment . This che ck sfairly well with res ult s found at Decatur, Ill ino is, 9

where , on the bas is of turbidi ty re co rd s, it was

estimated that only 75 percent of the sediment wastrap ped in the lake duri ng its life. Lake Deca turhad an original C/W ratio of 21. 8 acre-feet persquare mile; this had been reduced to 16. 1 by 1946.

By 1936, the C/W ra ti o of Lak e Calhoun hadbeen reduced to 10. 4 ac r e - f ee t pe r square mi le(see Table 1), and the lake probab ly tra ppe d only30 per cen t of the incomi ng sedi ment . By 1947,with a C/W ra ti o of 8. 6, the per cen tag e of se di ment trapped may have been as low as 20 percent.

The high rate of storage loss in Lake Calhounis due to the small-capacity lake developed in relation to the abo ve -n or ma l rate of sedimen t inflow from the watershed.

The 1936 survey and rep ort stated , "Th e findings of this survey indicate that Lake Calhoun hastoo large a watershed in relation to its storagecapacity." 3 This finding is confirmed by the p r e s ent study.

REMEDIAL MEASURES

Prac tica bili ty. The condition of the lake inthe last several years has been such that the useof the lake ha s been ha mp er ed . While the lakehas been utilized only for recreational purposes,

the advanced stage of sedimentation in the lakehas gre at ly red uce d the useful ness of the lake .In 1947 the deepest water in the lake was 5. 5 feetand 3 feet of thi s depth was cr ea te d by the r ai sein the spillw ay in 1946. Even aft er thi s ri se inwater level, much of the upper lake was uns uit abl efor boating and parts of it were practically inaccessible because of the shallow water.

The complet e drain ing of the lak e by the 1950spil lway fai lure stopped al l recreat ional act ivitie s dependent on the wa te r, such as swim min g,boating and fishing. Becau se of the money a l r ead yinvested by the lake ass oci ati on in the are a, it is

8. Engi neeri ng Hyd raul ics , Chapt er XII, SedimentTran spo rtat ion , by Car l B. Brown, p. 827. John Wiley andSons , New York, 1950.

9. Brown, C. B. , Stall, J. B . , and DeTurk , E. E. ,Causes and Effects of Sedimentation in Lake Decatur, StateWater Surv ey Divisio n, Bulleti n No. 37, U rbana , Illin ois,1946.

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believed des i rab le to consider me a s u r e s to r e cre ate and per pet uat e the lak e. Beca use of thegreat damage caused here by sediment in pastye ar s, howev er, pr ese nt efforts to rebuild andpe rp et ua te th e lake should be ba se d on a real is t icconcept of the sediment atio n pro blem . In ord erto prevent or minimize future sediment damages,the remedial measures at this lake should be cautious and well planned. In comp ari son to the r e

medial measures discussed herein, the lake owners should seriously consider the possibility ofcomplete abandonment of Lake Calhoun at the present si te . Thi s would de tr ac t from the value ofthe prese nt clubhouse and cotta ges, but the ar eaoffers great re cre at ion al facil i t ies even in theabsen ce of the lake. While thi s pro spe ct is not ave ry pl ea sa nt one, it should be given due consideration in light of the enormous sediment problem and other possibl e rem edi al me as ur es , including the probable present and future costs and

benefi ts of ea ch .

Raisin g the Dam. One of the fi rs t st eps us ually considered by lake owners in increasing storage capacity is that of raising the spillway andpos si bl y the dam. Such ac tion is us ua lly su bjec tto limitations as the original dam and spillwaywere possibly designed to give the most economical

proj ec t avai lable at that si te. As pr ev io us ly mention ed, the spil lwa y at Lake Calhoun was rai se dth re e feet in 1946. Sinc e Stat e Highway No. 17crosses the dam, the cost of removing and replacing the highway must be added to the cost of raising the dam alone.

The raising of the entire dam and spillwaywould flood additional lands near the present head

wat er s of the lake. A ri se of the lake level wouldput the lake 's edge very near the basement floorof the pr ese nt clubhouse. If such a ra is e werema de , the clu bhou se would have to be mov ed uphill . The top ogr aphy is such that an additionalelevation of 10 to 20 feet could be gained by moving the clubhouse up the steep bank.

If the present dam and spillway were raised10 feet above the pr es en t 718 M. S. L . , the lake

. created would have a capacity of approximately1280 acr e- fe et total , including the 112 acr e- fe etremai ning in the pr ese nt lake. This la rg er lakewould have a C/W ratio of about 98 acre-feet per

square mile of drainage ar ea. The pre sent wa te rshed rate of sediment production, with co rr es po nd ing inc rea se in tr ap efficiency, would deplete th isnew sto ra ge c apa cit y at 1. 0 to 1.5 per cen t peryear compared to the 3.21 percent per year suffere d in the past at Lake Calhoun. (See Table 1. )

Construction of An Additional Reservoir.Preliminary consideration has been given by thelake owners to construction of a new dam on FitchCreek at a site one-half mile south of the presentdam. At the sam e wa ter leve l elevat ion as the

present Lake Calhoun, su ch a lake would impo undabout 720 addit ional ac re -f ee t of wat er. In add i

tion to the 112 acre-feet remaining in the presentlake, t otal stor age would be 832 ac re -f ee t. Thecapacity-watershed ratio of the new project wouldthus be 63. 5 acr e-f eet per square mil e. The ra teof sediment production experienced in the past inthis drainage area would deplete such a lake at ara te of about 1. 6 to 2. 0 per cen t per ye ar . Th isis in comparison to the 3. 21 percent lost annuallyin pa st ye ar s in Lake Calhoun. (See Table 1. )

Dredging. In the pro gra m of sedimentat ioncontro l, consider ation mus t be given to the pos sibility of the removal of the sediment from thelake by dredg ing. Pa st studie s have shown thatthe unit cost of dredging is usually high in comparison to other methods of regaining stora ge spa ce.

As mentioned prev iou sly, the lake in it s 1947condition trapped only an estimated 20 percentof the sedim ent ent eri ng the lake . If the ent ir esedi ment in the lake wer e remo ved by dredging ,the lake would then trap approximately 70 to 80pe rc en t of the incoming sediment . On a long- termb as i s , under p resen t watershed conditions, the

dredged lake would silt at about the same rate asit has in the past.

Sediment Basins. Fro m a long-r ange plann ingstandpoint, upst ream sediment basin s mus t be co nsidered as tempo rary meas ure s. These basins siltup the same as reservoirs and eventually becomeineffective. In addition, the cost of con st ruc ti ngsuch a basin is generally greater per unit of storage than the re se rv oi rs it prot ects. 5 The buildingof numerous farm stock ponds properly constructedand located strategically could serve as miniaturesediment basins as well as to serve l ivestock

need s, fire protecti on, and fish production.

Vegetative Plantings. Prop er soil tr eat men t,adequate crop rotation, erosion control pr act ic eson sloping land, and a sound pa st ur e renovat ionand management program on this watershed areess ent ia l. In addition, the planting of tr ee s andshrubs in areas suited for woodland or wildlifeis highly de si re d. The local far m adv ise r andsoil conservation district personnel should be consulted for land use planning.

Thick-growing willows or other vegetationcould be introduced into the shallow areas of upperLake Calhoun. Such growths would ten d to re du cethe velocity of inflowing waters and induce sediment deposition above spillway level in the upperpar t of this lak e.

Watershed Treatment Prog ram. Sedimentation data obtained on Lake Calhoun indicate that

by 1947 the lake had been reduced to app roximat elyone-fourth of its origi nal capacity. This r e pr esents not only a loss to the community from thestandpoint of recreational facilities but also a severe loss to the far mer s. This sediment re pr esents many thousands of dollars in plant food andvaluable topsoil. Fer til ize r can be purc hased and

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ret urn ed to the land, but organic ma tt er and to p-soil cannot be readily or economically replaced.

It is far more economical to stop the sediment at its source than to dredge it from a lakeor build a new dam. The pos sib ili tie s and li mi tations of reducing sedimentation in a reservoirby means of co nse rva ti on measu res on th e wa te r shed have been reported in a study by Carl B.Brown.1 0 He s ta tes :

"Most of the sediment deposited in reservoirs of low C/W ratio is bed load material.The fine wash load, which our pr es en t co ns er vation program is reducing materially and proportionately muc h more th an bed lo ad , mostlyp as se s ove r the dam. In genera l , ther efore ,we are forced to conclude that reservoirs of low C/W ratio will not be protected by the soilc o n s e r v a t i o n d i s t r i c t s p r o g r a m s b e c a u s e :Fi rs t , these prog ra ms do not rapidly reducethe bed load inflow, which pr im ar il y cau sesthe silting; second, such reservoirs are silting rapidly and the time available to protectthem is too l imited with respect to t ime re

quired for application of control measures; andthird, the value of such reservoirs does notordinarily justify supplementary control workswhich would retard bed load movement. "

On the basis of the conservation survey madein the Lake Calhoun drainage area and describedea rl i er in this rep ort , a pro gr am of land tr ea tment has been drawn up. This pr og ra m is ba se don the agricultural use of the farm land in accordance with its physical capab ilities . The pr og ra mwill reduce greatly the loss of soil from the farm e r s ' f ields and wil l thus redu ce the sedimentreaching Lake Calhoun.

However, at pre sen t Lake Calhoun tr ap s onlyan estimated 20 percent of the sediment reachingthe lak e. Under this condition, only the la rg es tsize part icles are caught in the lake; the f iner ma te ri al pa sse s on over the spillway. The conse rv at io n p ro g r am outl ined in Table 8 for thewatershed will materially reduce the rate of sediment reaching the lake. This proposed wa ter sh edtreatment is the most strenuous use to which theland should be farm ed. It is estim at ed fro m thedata available that the soil loss under the proposedwatershed treatment program would reduce the

present loss of 69 , 467 tons an nual ly to 7, 629 tonsannually. This repre sents an 89 percent red ucti onof the soil leaving the fields. It is reas on ab le toassume that reducing the amount of soil lost fromthe fields will also result in smaller amounts ofsediment reaching the reservoir .

Tables 8 and 9 itemize a general watershedtre atm ent pro gra m. In ord er to develop a soundland use program on farms, assistance should beobtained from the farm adviser or the local soilconse rva t io n d is t r ic t . Al though the mea sur es

shown in Table 9 are designed largely to reduceshee t eros ion from the field, it is es tim at ed thatover 95 percent of the total load entering the reservoir is derived from this sou rce. The pro pos ed

prog ram would r e su l t in a reduction of approxi mately 84 percent of the total sediment load broughtto the lake. Beca use of other fact ors dis cus sedabove, however, principally the very low ca pa ci ty-waters hed rat io of Lake Calhoun, it is not be li ev ed

that a large reduction in the rate of sediment deposition in the lake can be accomplished by the watershed program . Although the sediment load re ac hing the lake can be reduc ed by 84 perce nt, or to16 percent of its present value, this 16 percentis approximately equal to the small portion of the

presen t load wh ic h no w stops in the lake. An 84percent red uc ti on would th us no t have a g rea t effect in protecting the lake.

To recommend a long-range watershed treatment program to reduce sedimentat ion in LakeCalhoun under its present condition may seem useles s. However, the methods and tre atm ent s p r e scribed in this program can be successfully usedto protect a larger Lake Calhoun if the dam werera is ed , or on a new sit e should ano the r lake be

buil t. Disregarding th e value of a wa ter sh ed t r e a t ment program as outlined in Table 8 for reducingsilting in the lake itself, the pr og ra m would re pa ythe farmers many times in benefits reaped fromgr ea te r yields and a perma nen t long range soi lmanagemen t pro gra m. This proposed pro gra mpro vi de s for fa rm in g the land in su ch a manner asto obtain the maximum economical returns over along period of time as well as to reduce the present soil losses from the fields approximately 89

percent .

The data in Table 8 showing the estimated soilloss in the watershed from the present farmingsyst em as compared to the proposed pro gra m we redeveloped from the soil conservation survey mapsand available re se ar ch information.11 These soilloss figures ar e relativ e and ar e espe ciall y va luable in co mpa rin g the dif ferenc es between thep r e s en t and proposed p r og ra m .

In comparing the present with the proposedprogram the greatest re duct ion in so il loss occurs -on the culti vate d land . The soi l los s from the

p re sen t p rog ram is over te n t i mes g rea t e r thanfrom the proposed watershe d pro gra m. The gre atreduc tion in soil los s is due larg el y to growingless cultivated crops on the sloping land and tothe use of conservation prac t ice s. Pre sen t er osion ha zar ds in the wat ers hed ar e illust rat ed inFi gu re s 13 and 14. The pr op er use of ero sio ncontrol prac t ice s such as contouring, t err aci ngand st ri p cropping, can reduce soil losse s froma field 30 to 85 perc ent. All acr eag e adju stme ntsfrom the present to the proposed land use programare minor .

10. Brown, Car l B. , Aspect s of Protec ting StorageRes erv oi rs by Soil Conse rvati on, Jour nal of Soil and WaterConservation, Vol. I, No. 1, July, 1946.

11. Van Dor en, C. A. and Klin geb iel, A. A. , Slopeand Prac tic e Limitat ions for Illinois. Mimeograph Rel ease ,Urbana, Illinois, January 1948.

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Table 9

Estimated Conservation Practices and Rotations on CroplandLake Calhoun Watershed

The suggested amounts and kinds of rotations

and erosion control practices needed in the water

shed treatment program may be found in Table 9.No erosi on con trol pract ices are ne ed ed on 2252

acres of the 6667 acres in cultivation in the water

shed. The major erosio n control pr act ice s r ec

ommended ar e: contouring 2827 ac re s, st ri p cr op

ping 771 a c re s , and te r racing 694 a c r e s . Addi

tional te rr ac es would further reduce soi l lo ss.

FIG. 13. SLOPI NG LAND FA RM ED UP AND DOWN

THE HILL RESULTS IN HIGH SOIL LOSSES.

The most intensive rotation recommendedallows the land to remain in grasses and legumesat least one-fourth of the tim e. This rotati on isrecommended on level land and on gently slopingland (less than 5 percent) where contouring or terracing is used. The reco mmen ded rotat ions r e quiring grasses and legumes three or more yearsout of every five are designed for the steep or

badly erod ed land that is st il l su ita bl e for l imitedcultivation.

FIG . 14. WATERWAYS SHOULD BE SEE DED TO GRASS

TO PREVENT WASHING.

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F IG. 15 . NE T INCOME P ER AC RE , P HYS ICAL LY

CO MP AR AB LE HIGH AND LOW CONS E RVATI ON F ARMS ,

MCL EAN COUNTY , 1936-19 45 .

Cost and Benefits of Cons erva tion . Studiesof actual farms in the state show that the application of soil conservation measures by the farmerhimself can be justified economically because ofincreased crop yields and increased net farm income.

The long-time benefits of conservation arecerta in. However, consid erable effort and mon eymust be expended before posit ive results areachieved. Conservation benefits ar e dem ons tr at edby studies co mparing matched high and low con servation farms in McLean County for the period1936-1945. The far ms compared had sim il ar l and -use capabilities and were similar in size but onegroup of farmers used soil and water conservation

pr ac t i ce s an d the ot her group did no t use them.Figures 15 and 16 show the benefits of conservation in terms of income changes and crop yieldchanges.

Conservation costs including fertilizer and

seed amounted to approximately $35 per acre onthe hig h- con ser vat ion fa rm s. This was abouttwice the am ount spent for co nser vat ion on the

F IG. 16 . CRO P YIEL D INDEX, P HYS ICALLY COM

PA RA BL E HIGH AND LOW CONSERVATION FARMS, MCL EA N

COUNT Y, 1936- 1945 . (Av era ge y ie l d s o f a l l c ro ps fo r a l l

f a rm s equ a ls 100 . )

low-conservation farms.

The high-conservation farms had average netincomes of $3. 46 per acr e per year mor e for the10-yea r per iod . (This was after accounting forall exp ens es, including costs of conser vatio n. )This increased income amounted to $5, 536 for a16 0- ac re fa rm for the 10-ye ar per iod . At 1945

pr ices th e increased net inc om e from conservation amount ed to $4. 77 per a cr e, or $ 7, 632 fora 160-acre farm for a 10-year period.

Conservation costs and benefits in the LakeCalhoun watershed would be comparable or greaterthan tho se in the Mc Le an County study. Whilethe McLean County farms studied have a higherpr op or ti on of til la bl e land, thi s would be offset bythe present unproductive pastureland in the LakeCalhoun watershed which would be brought into

prof it ab le pr od uc tio n by ap pl ic at ion of a completeconservatio n plan. The Lake Calhoun wat er she dis more of a livestock producing area and recent

stud ies show tha t liv est ock fa rm er s often gainmore from a conservation program than do grainfa rme rs .

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APPENDIX

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Table A

Distribution of Slope Classes in Each Soil GroupLake Calhoun Watershed

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Table B

Dis tr ibut ion of Land Use Classes in Each Soil Group

Lake Calhoun Watershed

Table C

Dis tr ibut ion of Land Use Cl ass es in Each Slope Class

Lake Calhoun Watershed

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Table D

Land Capability Compared with Existing Land Use at Time of SurveyLake Calhoun Watershed

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Table E

Distr ibution of Erosion Groups in Each Soil GroupLake Calhoun Watershed

Table F

Distr ibution of Erosion Groups in Each Slope ClassLake Calhoun Watershed

Table G

Distr i bution o f Ero si on Gro ups in Each Land Use Cla ssLake Calhoun Watershed

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REPORTS OF INVESTIGATIONS

ISSUED BY THE STATE WATER SURVEY

No. 1. Tempera tur e an d Turbidi ty of Some River Waters in Illinois. 1948.

No . 2. Gr oun dw at er Resources in Winnebago County, wi th Specif ic Referenceto Cond itio ns at Rock ford . 1948.

No . 3. Radar and Rainfall . 1949.

No. 4. Th e Si lt P rob l em at Spri ng Lake , Macomb, I l linois . 1949. *

No . 5. Inf ilt rati on of So il s in the Peor ia Area . 1949.

No. 6. Groundwater Resources in Champaign Coun ty . 1950.

No. 7. The Silt ing of Ridge Lak e, Fox Ridge State Park , Charleston, I l l inois .1951.*

No. 8. The Si lt ing of Lake Chau tauqua, Havana, Il linois . 19 51 .

No. 9. The Si lt in g of Carbondale Re se rvo i r , Carbondale, I l linois . 19 51.

No. 10. The Si lt ing of Lake Bracken, Galesburg , I ll inois. 19 51 .

No. 11. I rr igat ion in I ll inois. 19 51 .

No . 12. Th e Sil ti ng of West Frank fo r t Res e rvo i r , Wes t F rank for t , I l l inois .1951.

No. 13. Studie s of Thunders to rm Rai nfa ll wi th Dens e Raingage Networks an dRadar. 1952

No . 14. The Storm of Jul y 8, 1951 in North Cent ra l I ll inois . 1952

No. 15. The Si lt ing of La ke Ca lho un , Galv a, I ll inois . 1952

*Out of print.