Floodplain Mapping Models

Discussion & Objectives• Floodplains can be difficult and frustrating to map in

“traditional” soil survey.– Why?– Do you agree?

• Without an underlying geomorphic model, floodplain mapping may be dependent on the mapper.– What does this mean?– Do you agree?

• Objectives– Discuss some fluvial mapping models in the lower Missouri

river valley• SSURGO• LiDAR (detailed mapping)

Consider a mapping project in a river valley…. or a benchmark soil update project….

• How do you start to organize your mental models?

• What will you use to establish testable mapping hypotheses?

• What tools/techniques will you use?• Considerations/questions about the system?

Etc.• Discussion….

Fred’s response(let’s see how well I did)

• What is the nature of the fluvial system?– Sediment sources

• Loess-covered uplands vs glacial uplands vs cherty limestone residuum vs soft cacareous cretaceous sediments…. or mixtures.

– River system• Braided vs meandering; bedrock controls; faulting; etc.• Post-settlement modifications (levees, drainage, leveling, channelization)

• Possible tools to discern geomorphic surfaces– LiDAR (NED DEMs probably inadequate)– Aerial photography/imagery– Go out and look (clean windshield)

• Hole mapping?– Last resort

Case Study:

Examine the mapping model in the Missouri R valley of NW MO

What were the characteristics of the pre-settlement lower Missouri River?

Missouri River

Missouri River

Examine mapping model in the Missouri R valley of NW Missouri (and SE NE)

SSURGO soils in the Mo R valley

Consider a “classic” model of floodplains: - Sand, silts, clay - Similar to mid-20th century mapping in the Mo R bottoms

How well does the mapping fit the meander belt model of the lower Mississippi?

Consider the early 19th century location of the Missouri River.

How closely is the alluvial stratigraphy related to the current riverbed?

Many soils are “two-tiered”, split families.

Complex depositional history.

“Prominent” scarp noted in Atchison county mapping - 1 to 3 meters high - windshield technique

(Low) floodplain soils - carbonates to surface

(High) floodplain step soils - carbs below about 50cm

How well does this model work?

County boundaries added to the floodplain surfaces model.

How can this model be used in update activities for MLRA 107B?

Early 19th century River superimposed on the floodplain surfaces SSURGO model.

Pretty good match! (except in NE)

Low floodplain; calcareous to surface

High floodplain; calcareous at >24”

Natural levee

co-si calcareous

backswamp

Wet, clayeyFootslope; cumulic Hapludoll, co-si

Note: existing soil lines only partially follow landforms shown here

Missouri River floodplain, NW MO

N

Consider the confluence of the Chariton R and the Missouri R.

Missouri –Chariton confluence, with LiDAR backdrop

Chari

ton R

1m LiDAR, resampled to 5m

Missouri R

Is this the source of the pre-settlement Chariton R sediments?

Soils of the Chariton R floodplain (& other local upland sources)

Mo R

High floodplain of the Missouri R (as defined by soil survey)

Low floodplain of the Missouri R (as defined by soil survey)

Mo R

Surfaces as derived from soil survey

MO River floodplai

n

MO River Floodplain-

stepChariton R floodplain

Can elevation (absolute) be used to separate surfaces? 190m class break

Works well here

Natural levee (high)

Sloughs (low)

High, loess-covered terrace at Malta Bend on the Missouri River, central

Missouri

10m DEM

Some of Missouri’s most productive agricultural soils are on this surface

Joy series: fi-si Aquic Hapludolls

Missouri R.

N

Location of Cora Island mapping area

Missouri River floodplain, St. Charles county (near St. Louis)

Detailed (Order 1) floodplain mapping

Low-relief terrain; difficult to see the soil-landscape relationships

10m NED DEM – not much help

LiDAR – wow!Testable hypotheses about soil variability are now apparent.

MUSYM MUNAME Series TaxClass1 1 - Lowmo Blake fi-si Aquic Udifluvents2 2 - Peers Blencoe c/l Aquertic Hapludolls3 3 - Blencoe Grable co-si/s Mollic Udifluvents4 4 - Sansdessein occass flooded Haynie co-si Millic Udifluvents5 5 - Grable Lowmo co-si Fluventic Hapludolls6 6 - Parkville Moville co-si/c Aquic Udifluvents7 7 - Haynie Parkville c/l Fluvaquentic Hapludolls8 8 - Moville Peers fi-si Fluvaquentic Hapludolls9 9 - Treloar - Haynie complex Sansdessein f Fluvaquentic Vertic Endoaquolls

10 10 - Blencoe - Grable complex Treloar s/l Oxyaquic Udifluvents11 11 - Sansdessein freq flooded12 12 - Haynie - Blake - Treloar complex13 13 - Water

Mapping closely follows landscape patterns

EMI patterns reflect the LiDAR and soils patterns, with lower, wetter areas of finer textured soils having high readings.

Discussion (if we have time)

• Other experiences with fluvial systems mapping?

• How can you avoid “hole mapping”?• Techniques for creating a soil - geomorphic

surface model for soil survey?