TASK 14-1 Inspection Memo #3 11 11 2013€¦ · 3.1 Observations from November 1, 2011, Inspection 1. Upstream Flanking – There was no evidence that there has been any erosion at

M&T/Llano Seco Fish ScreenFacility Short-Term/Long-Term Protection

Maintenance Inspection and Report #3 1

MEMORANDUM

TO: Jim Well, Ducks Unlimited

FROM: Mike Harvey, PhD, PG

SUBJECT: M&T/ Llano Seco Fish Screen Facility Short-Term/Long-Term ProtectionProject (Project No. US-CA-62-2)

Maintenance Inspection and Reports (Subtask 6.1)

Inspection Report No.3

DATE: November 12, 2013

1 Introduction

Prior to selection and implementation of a final solution to the sedimentation problems at theM&T fish screens and pump intakes, temporary bank protection consisting of approximately1,500 LF of rock-toe/brush revetment was placed on the west bank of the Sacramento River onthe U.S. Fish and Wildlife Service’s Capay Unit in October 2007. The purpose of the revetmentwas to prevent further bank erosion and river migration (Figures 1 through 5), therebypreserving options for solution of the M&T/Llano Seco pump intakes and fish screens problems.Because the revetment was designed as an interim and temporary measure, there was anexpectation that some maintenance would be required. The purpose of this memorandum is toreport on the condition of the revetment and the need for any maintenance, if required.

This Technical Memorandum summarizes the post-construction observations that were madeduring three inspections of the revetment; April 12, 2010, November 1, 2011, and November 7,2013. This Memorandum builds on the previous 2 reports (Tetra Tech, 2010 and 2012) andprovides a record of the performance of the revetment since construction in October 2007.

1.1 Background

The interim revetment was designed to provide toe protection only to the eroding bank andthere was a general expectation that the upper, nearly vertical and unprotected portion of thebank, would continue to erode until a lower bank angle developed that would be colonized byplants and, thereby, be stabilized. Approximately 5 tons/lineal foot of rock were placed at thebase of the bank by excavators working from the top of the bank. The median size of the rockused was 0.75 feet, the 30

thpercentile was 0.63 feet and the 100

thpercentile was 0.94 feet.

The top of the revetment was set an elevation of about 119 feet, which corresponded to adischarge of approximately 15,000 cfs, which has a 42-percent exceedence on the mean dailyflow-duration curve at the Hamilton City gauge, located about 7 miles upstream (Figure 6). Forenvironmental mitigation purposes, during construction woody debris was added to thestructure at two elevations: (1) approximately Elevation 118 feet within the structure, whichcorresponds to a discharge of about 12,000 cfs (50-percent exceedence on the mean dailyflow-duration curve), and (2) on the top of the structure. The top of the rock was slopedoutwards (towards the river) at a grade of 10H:1V and the area between the top of the rock andthe bank was backfilled with spoils from the tie-back excavations to prevent any entrapment offish (Figures 7 through 10).



Photographs of the structure taken in March 2008 after the first period of high flows followingconstruction are provided for reference purposes. Figure 11 shows that the upstream end ofthe structure and pre-existing bank vegetation are intact. Figure 12 shows that the woodyvegetation emplaced on the top of the revetment is still in place and that there had beendeposition of sediment (primarily fine sands and silts) on top of and within the upper layer of therock. Figure 13 shows that there was erosion and retreat of the unprotected portion of thebank, but there was no evidence of scour behind the rock. Figure 14 shows that the within-rock woody material was still in place.

2 Field Inspections

2.1 April 12, 2010 Inspection

The first post-construction inspection of the revetment was conducted on April 12, 2010, whenthe flow in the river was about 11,000 cfs. Since construction, the revetment had experiencedpeak flows of 56,000 cfs (January 26, 2008), 43,000 (February 17, 2009) and 64,000 cfs(January 26, 2010). During the course of the field inspection, the following conditions that couldrequire maintenance were assessed:

1. Flanking of the upstream end of the structure,

2. Loss of rock from the structure itself due to local scour at the base,

3. Loss of woody material incorporated within and placed upon the top of the structure,

4. Excessive erosion of the unprotected portion of the bank and scour along the contactbetween the rock toe and the bank, and

5. Excessive erosion off the downstream end of the structure.

2.2 Observations from April 12, 2010, Inspection

1. Upstream Flanking – There was no evidence that there has been any erosion at theupstream end of the structure (Figure 15). Comparison with Figure 11 indicates that therehas been little or no change at the upstream end of the site since construction.

2. Loss of Rock – There was no evidence of loss of rock at any location along the entire1,500 feet of the structure (Figure 16). The crest of the rock was sharp along the entirerevetment and there was no evidence of erosion scarps.

3. Loss of Woody Material – Although the water surface was generally above the elevation ofthe woody debris included within the structure, there was evidence of its presence at anumber of locations (Figure 17). The fact that the woody material was located below thewater surface at a discharge (11,000 cfs) below the design discharge (12,000 cfs) suggeststhere may have been some bed scour along the revetment, but it could also easily be withinthe margin of error for the rating curve that was used for design purposes. From a biologicalperspective, the woody debris is being inundated and thus providing habitat for more thanthe designed 50 percent of the time. Woody debris piles placed on the top of the revetmentwere intact (Figure 18) and appear to be sites of preferential establishment of boxeldersand other plants (Figure 19), probably because of their effects on local flow velocities.



4. Excessive Bank Erosion – Upper bank erosion was occurring at a number of locationsalong the site, as expected (Figure 20). The ongoing erosion is lowering the bank angle asthe bank rotates backwards from the armored toe. However, there was no evidence of anyscour along the contact between the rock and the bank (Figure 21), and it is clear thatwoody vegetation (primarily willows) has become established at the base of the bank and onthe lower angle portions of the bank (Figure 22).

5. Excessive Downstream Erosion – Observation of the downstream end of the revetmentdid not indicate that there had been any significant erosion of the bank downstream of therevetment (Figure 23) and there does not appear to have been any loss of rock (Figure24).

2.3 Conclusions and Recommendations Following April 12, 2010, Inspection

Based on the observations of the interim revetment on April 12, 2010, it was clear that therewere no requirements for maintenance of the site following a range of peak flows up to 64,000cfs. However, it was recommended that the site be re-inspected following the winter high flowsof 2010/2011. It was recommended also that inspection of the site should be done when flowsare in the 6,000- to 8,000-cfs range so the outboard side of the revetment could be observed.

3 November 1, 2011 Inspection

The second post-construction inspection of the revetment was conducted on November 1,2011, when the flow in the river was about 7,190 cfs. Since construction, the revetment hadexperienced peak flows of 56,000 cfs (January 26, 2008), 43,000 cfs (February 17, 2009),64,000 cfs (January 26, 2010) and 102,528 cfs (March 21, 2011). During the course of the fieldinspection, the following conditions that could require maintenance were assessed:




4. Excessive erosion of the unprotected portion of the bank and scour along the contactbetween the rock toe and the bank, and

5. Excessive erosion off the downstream end of the structure.

6. Toe scour along the revetment.

3.1 Observations from November 1, 2011, Inspection

1. Upstream Flanking – There was no evidence that there has been any erosion at theupstream end of the structure (Figure 25). Comparison with Figures 11 and 15 indicatesthat there has been little or no change at the upstream end of the site since construction.

2. Loss of Rock – There was no evidence of loss of rock at any location along the entire1,500 feet of the structure (Figures 26 through 29). The crest of the rock was sharp alongthe entire revetment and there was no evidence of erosion scarps.



3. Loss of Woody Material – The water-surface elevation at a discharge of 7,190 cfs is belowthe large woody debris included within the structure at construction (Figure 6). Woodydebris piles placed on the top of the revetment and within the revetment were intact alongthe entire site (Figures 30 through 33). The large woody debris piles anchored on the topof the structure appears to be sites of preferential establishment of boxelders, sycamoreand willows (Figure 34), probably because of their effects on local flow velocities.

4. Excessive Bank Erosion – Upper bank erosion continues to occur at a number of locationsalong the site, as expected (Figures 20 and 21). The ongoing erosion is lowering the bankangle as the bank rotates backwards from the armored toe. However, there was noevidence of any scour along the contact between the rock and the bank (Figure 21), and itis clear that woody vegetation (primarily willows) has become established at the base of thebank and on the lower angle portions of the bank (Figure 22).

5. Excessive Downstream Erosion – Observation of the downstream end of the revetmentdid not indicate that there had been any significant erosion of the bank downstream of therevetment (Figure 35) and there does not appear to have been any loss of rock (Figure36).

6. Toe Scour along the Revetment – Comparison of the January 2010 and June 2011bathymetric surveys of the M&T Reach (Figure 37) indicate that the high flows of March2011 may have caused about 2 feet of scour along the revetment. However, the fieldinspection did not reveal any loss of rock resulting from the toe scour.

3.2 Conclusions Following November 1, 2011, Inspection

Based on the observations of the interim revetment on April 12, 2010, and November 1, 2011, itwas clear that there were no immediate requirements for maintenance of the site following arange of peak flows up to 102,528 cfs. At the highest discharge experienced since construction,the left overbank above the toe rock revetment was overtopped in 2011, but there was noevidence of either accelerated erosion of the upper bank or damage to the revetment itself.Both the up- and downstream transitions into and from the revetment show no signs ofsignificant erosion. Significant numbers of riparian plants have volunteered onto both the top ofthe rock revetment and onto the reduced-angle lower bank slope above the contact with therevetment. There does not appear to have been any loss of large woody debris from thestructure. Based on the field observations it appears that the toe rock revetment wasperforming well and continued to maintain the current river alignment.

4 November 7, 2013, Inspection

The third post-construction inspection of the revetment was conducted on November 7, 2013,when the flow in the river was about 6,000 cfs. Since construction, the revetment hadexperienced peak flows of 56,000 cfs (January 26, 2008), 43,000 cfs (February 17, 2009),64,000 cfs (January 26, 2010), 102,528 cfs (March 21, 2011), 44,073 cfs (March 28, 2012) and85,620 cfs (December 3, 2012). During the course of the field inspection, the followingconditions that could require maintenance were assessed:






4. Excessive erosion of the unprotected portion of the bank and scour along the contactbetween the rock toe and the bank,

5. Excessive erosion off the downstream end of the structure, and

6. Toe scour along the revetment.

4.1 Observations from November 1, 2011, Inspection

1. Upstream Flanking—There was no evidence that there has been any erosion atthe upstream end of the structure (Figures 38 and 39). Comparison with Figures11, 15 and 25 indicates that there has been little or no change at the upstream endof the site since construction.

2. Loss of Rock—There was no evidence of loss of rock at any location along theentire 1,500 feet of the structure (Figures 40 through 43). The crest of the rock wassharp along the entire revetment and there was no evidence of erosion scarps.Comparison with Figures 26 through 29 indicates that there has been little or nochange in the shape of the crest or significant loss of rock.

3. Loss of Woody Material—The water-surface elevation at a discharge of 6,000 cfsis below the large woody debris included within the structure at construction (Figure6). Woody debris piles placed on the top of the revetment and within the revetmentwere intact along the entire site (Figure 44). The large woody debris piles anchoredon the top of the structure appears to be sites of preferential deposition of finer(sand and silt) sediment and establishment of boxelders, sycamore and willows(Figures 45 through 50), probably because of their effects on local flow velocities.Since the 2011 inspection, there has been a significant increase both in the densityof the woody vegetation and the size of the individual shrubs and trees growing onthe revetment.

4. Excessive Bank Erosion—Upper bank erosion continues to occur at somelocations along the site, as expected (Figures 20 and 21). The ongoing erosion islowering the bank angle as the bank rotates backwards from the armored toe.However, there was no evidence of any scour along the contact between the rockand the bank (Figures 51 and 52), and it is clear that woody vegetation (primarilywillows) has become established at the base of the bank and on the lower angleportions of the bank.

5. Excessive Downstream Erosion—Observation of the downstream end of therevetment did not indicate that there had been any significant erosion of the bankdownstream of the revetment (Figure 53) and there does not appear to have beenany loss of rock (Figure 54).

6. Toe Scour along the Revetment—Comparison of longitudinal profiles along thetoe of the revetment that were developed from bathymetric surveys of the M&TReach in 2010, 2011, 2012 and 2013 indicate that the high flows of March 2011(102,528 cfs) may have caused some scour along the revetment, but the thalweg



aggraded the following year when the peak flow was low (44,073 cfs) (Figure 55).Following the somewhat higher peak flow in 2012 (85,620 cfs), there was somescour into the 2011 deposits. However, the field inspection did not reveal any lossof rock resulting from the toe scour.

4.2 Conclusions Following November 7, 2013, Inspection

Based on the observations of the interim revetment on April 12, 2010, November 1, 2011, andNovember 7, 2013, it is clear that there are no immediate requirements for maintenance of thesite following a range of peak flows up to 102,528 cfs. At the highest discharge experiencedsince construction in 2007, the left overbank above the toe rock revetment was overtopped in2011 but there was no evidence of either accelerated erosion of the upper bank or damage tothe revetment itself. Both the up- and downstream transitions into and from the revetment showno signs of significant erosion. Significant numbers of riparian plants have volunteered ontoboth the top of the rock revetment and onto the reduced-angle lower bank slope above thecontact with the revetment. There does not appear to have been any loss of large woody debrisfrom the structure. Based on the field observations, it appears that the toe rock revetment isperforming well and continues to maintain the current river alignment six years after it wasconstructed.



Figure 1. Photograph of the upstream end of the site prior to construction of the rock-toe/brush revetment. (Photo taken on 10/24/2006)

Figure 2. Photograph of the middle part of the site prior to construction of the rock-toe/brush revetment. (Photo taken on 10/24/2006)



Figure 3. Photograph of the apex of the eroding bend prior to construction of the rock-toe/brush revetment. (Photo taken on 10/24/2006)

Figure 4. Photograph of the middle part of the downstream part of the site prior toconstruction of the rock-toe/brush revetment. (Photo taken on 10/24/2006)



Figure 5. Photograph of the downstream end of the site prior to construction of the rock-toe/brush revetment. (Photo taken on 10/24/2006)



Figure 6. Typical sections of the rock-toe/brush revetment showing design flows andelevations.

25% Exc., Q = 24,840 cfs

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42% Exc., Q = 15,000 cfs

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42% Exc., Q = 15,000 cfs

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50% Exc., Q = 12,180 cfs



Figure 7. View downstream of the rock toe being emplaced during construction of therevetment. The top of the rock is at Elevation 119 feet. (Photo taken on10/30/2007)

Figure 8. View upstream of the rock toe being emplaced during construction of therevetment. Note the woody material incorporated into the revetment at aboutElevation 117 feet. (Photo taken on 10/30/2007)



Figure 9. View of woody material being placed on the top of the revetment at aboutElevation 119 feet during construction of the revetment. (Photo taken on10/30/2007)

Figure 10. View upstream of backfill in place between the rock revetment and the bankslope during construction. (Photo taken 10/30/2007)



Figure 11. View upstream of the upstream end of the revetment showing the presence ofthe pre-construction vegetation on the upstream bank. (Photo taken on03/12/2008)



Figure 12. View of intact woody debris on top of the revetment as well as sedimentdeposition on top of the rock following the first higher winter flows afterconstruction. (Photo taken on 03/12/2008)

Figure 13. View downstream of bank erosion caused by the first higher winter flows afterconstruction. (Photo taken on 03/12/2008)



Figure 14. View of top of revetment showing the presence of woody material both on top ofthe revetment and encased within the structure following the first higher winterflows after construction. (Photo taken on 03/12/2008)

Figure 15. View of the upstream end of the revetment and the pre-construction riparianvegetation growing on the bank upstream of the structure. Flow in the river wasabout 11,000 cfs. (Photo taken on 04/12/2010)



Figure 16. View upstream of the revetment showing the presence of the woody debris pilesthat were constructed on top of the structure. Flow in the river was about 11,000cfs. (Photo taken on 04/12/2010)

Figure 17. View of the top of submerged woody material that was incorporated into therevetment at about Elevation 117 feet. Flow in the river was about 11,000 cfs.(Photo taken on 04/12/2008)



Figure 18. View downstream of the top of the revetment showing the woody debris pilesthat were placed and cabled onto the revetment. Flow in the river was about11,000 cfs. (Photo taken on 04/12/2010)

Figure 19. Close up view of a woody debris pile cabled onto the top of the revetmentshowing volunteer woody plants growing within and around the debris pile. Flowin the river was about 11,000 cfs. (Photo taken on 04/12/2010)



Figure 20. View downstream of eroding upper bank above the top of the revetment that iscausing the bank angle to be reduced. Flow in the river was about 11,000 cfs.(Photo taken on 04/12/2010)

Figure 21. View downstream showing eroding upper bank but no evidence of any scour ofthe backfill material at the base of the bank. Flow in the river was about 11,000cfs. (Photo taken on 04/12/2010)



Figure 22. View upstream of willow growth along the top of the revetment and at the base ofthe eroding bank. Flow in the river was about 11,000 cfs. (Photo taken on04/12/2010)

Figure 23. View downstream of the downstream part of the revetment with vegetationgrowing at the toe of the bank and on the top of the revetment. Flow in the riverwas about 11,000 cfs. (Photo taken on 04/12/2010)



Figure 24. View upstream of the downstream end of the revetment and the downstream tieback. Flow in the river was about 11,000 cfs. (Photo taken on 04/12/2010)

Figure 25. View of the upstream end of the rock revetment and transition to unprotectedbank at a flow of about 7,200 cfs. Note the presence of the willows growing onthe bank indicating that there has been little or no erosion at the upstream end ofthe revetment. (Photo taken on 11/01/2011)



Figure 26. Upstream view of the upstream end of the toe rock revetment at a flow of about7,200 cfs. Note presence of riparian vegetation as well as the large woody debrisemplaced within the rock during construction. There is no evidence of loss ofrock. Note the larger anchor boulders that were used to secure the large woodydebris emplaced on the top of the revetment. (Photo taken on 11/01/2011)

Figure 27. Upstream view of the upper section of the toe rock revetment at a flow of about7,200 cfs. Note the large woody debris emplaced on the top of the rock andwithin the rock during construction and the riparian vegetation that hasvolunteered onto the top of the rock especially in the vicinity of the large woodydebris placed on the top of the rock. (Photo taken on 11/01/2011)



Figure 28. Close up view of the rock toe within the middle section of the revetment at a flowof about 7,200 cfs. There is no evidence of loss of rock. (Photo taken on11/01/2011)

Figure 29. Close up view of the rock toe within the lower end of the revetment at a flow ofabout 7,200 cfs. There is no evidence of loss of rock. (Photo taken on11/01/2011)



Figure 30. Close up view of the upper section of the toe rock revetment at a flow of about7,200 cfs. There is no evidence of loss of rock. (Photo taken on 11/01/2011)

Figure 31. Upstream view of the middle section of the toe rock revetment at a flow of about7,200 cfs. Note the large woody debris emplaced on the top of the rock andwithin the rock during construction. (Photo taken on 11/01/2011)



Figure 32. Upstream view of the middle section of the toe rock revetment at a flow of about7,200 cfs. Note the very dense volunteered riparian vegetation species growingon the top of the rock and the presence of the emplaced large woody debris onthe top of the rock and within the rock. (Photo taken on 11/01/2011)

Figure 33. Upstream view of the lower (downstream) end of the toe rock revetment at a flowof about 7,200 cfs. Note the presence of volunteered riparian vegetation speciesincluding sycamore, box elder and willows on the surface of the rock. (Phototaken on 11/01/2011)



Figure 34. Upstream view of the lower end of the toe rock revetment at a flow of about7,200 cfs. Note presence of volunteered riparian vegetation species as well asemplaced large woody debris on the top of the rock and within the rock. There isno evidence of loss of rock from the revetment. (Photo taken on 11/01/2011)

Figure 35. Downstream end of revetment at a flow of about 7,200 cfs. Note presence ofwillows growing on the bar which indicates there has been no retreat of the bankdownstream of the toe rock. (Photo taken on 11/01/2011)



Figure 36. Close up view of the downstream end of the toe rock at a flow of about 7,200cfs. Rock is intact and there appears to be little loss of rock at the downstreamend. (Photo taken on 11/01/2011)



Figure 37. Elevation changes in the M&T/Llano Seco reach between the January 2010 andJune 2011 surveys.



Figure 38. View downstream of the upstream end of the toe rock revetment at a flow ofabout 6,000 cfs. (Photo taken on 11/07/2013)

Figure 39. View downstream of the willow vegetation established on the bank upstream ofthe rock toe revetment indicating the absence of any flanking of the structure ata flow of about 6,000 cfs. (Photo taken on 11/07/2013)



Figure 40. View upstream of the outside face of the rock toe revetment near the upstreamend of the structure at a flow of about 6,000 cfs. (Photo taken on 11/07/2013)

Figure 41. View upstream of the outside face of the rock toe revetment near the middle ofthe structure at a flow of about 6,000 cfs. (Photo taken on 11/07/2013)



Figure 42. View upstream of the outside face of the rock toe revetment at the lower end ofthe structure at a flow of about 6,000 cfs. (Photo taken on 11/07/2013)

Figure 43. View upstream of the outside face of the rock toe revetment at the downstreamend of the structure at a flow of about 6,000 cfs. (Photo taken on 11/07/2013)



Figure 44. Large woody debris anchored to the top of the revetment in 2007. (Photo takenon 11/07/2013)

Figure 45. Sand and silt deposits in the vicinity of woody debris anchored to the top of therevetment in 2007. (Photo taken on 11/07/2013)



Figure 46. Mixed species of woody vegetation including willows, sycamore and boxeldergrowing on the rock toe revetment. (Photo taken on 11/07/2013)

Figure 47. View upstream of the woody vegetation growing on the top of the revetment nearthe upstream end of the revetment. (Photo taken on 11/07/2013)



Figure 48. View upstream of the woody vegetation growing on the top of the revetment nearthe middle of the revetment. (Photo taken on 11/07/2013)

Figure 49. View upstream of the woody vegetation growing on the top of the revetment nearthe lower end of the revetment. (Photo taken on 11/07/2013)



Figure 50. View upstream of the woody vegetation growing on the top of the revetment nearthe downstream end of the revetment. (Photo taken on 11/07/2013)

Figure 51. View upstream of relatively low angle, stable upper bank slope that has resultedfrom bank retreat above the rock toe near the middle of the revetment. (Phototaken on 11/07/2013)



Figure 52. View upstream of relatively low angle, stable upper bank slope that has resultedfrom bank retreat above the rock toe towards the upstream end of the revetment.(Photo taken on 11/07/2013)

Figure 53. View upstream of willows growing on the lower bar surface downstream of therock toe revetment at a flow of about 6,000 cfs. (Photo taken on 11/07/2013)



Figure 54. View upstream of the downstream end of the rock toe revetment showing no lossof rock or bank erosion off the downstream end of the rock at a flow of about6,000 cfs. (Photo taken on 11/07/2013)



Figure 55. Longitudinal profiles of the channel bed along the toe of the rock toe revetment. Also shown is the profile along thetop of the revetment. Station 0 is the downstream end of the revetment.

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Documents

TASK 14-1 Inspection Memo #3 11 11 2013€¦ · 3.1 Observations from November 1, 2011, Inspection 1. Upstream Flanking – There was no evidence that there has been any erosion at