1. Fluvial Geomorphology
Prof. Dr. Paul J. DuBowy
Ecohydrology Associates, LLC
Lovell, Wyoming USA

2. Outline Geomorphologic Concepts and Terms
Consequences to Floodplain Ecosystems
Biogeochemistry/Redox Reactions
Hydric Soils
Vegetation Zonation

3. Fluvial Geomorphology
Much recent attention has focused on “natural stream channel design” = Fluvial Geomorphology.
While this scientific discipline was relatively unknown as an applied science until recent years, recent application of the science to restoration designs shows a great deal of promise for effective stream channel management.
Many years of extensive research in stream function and the factors that influence stream channel stability provide the backbone for application of this science.

4. Fluvial Geomorphology 2
While some aspects of the discipline are unique, it is truly a multidisciplinary field, which requires knowledge of engineering, geology, biology, hydrology, soil science, and other scientific disciplines.
Fluvial Geomorphology, taken literally, means the study of river-related landforms.
Direct application of the science to stream channel restoration.
Sediment transport, stable channel forms, hydraulic structure, stream channel assessment, and design practices.

6. Macro- to Micro-geomorphology
FISRWG

7. Cross-section

8. Channel Morphology

9. Stream Morphology

10. Sinuosity

12. Slope Calculations

13. Balance of Dynamic Forces
Rosgen
Rosgen
(Sediment Load) × (Sediment Size) ∝ (Stream Slope) × (Stream Discharge)

14. Erosion/deposition (aggradation/degradation)
Head Cutting
Erosion
Long-term storage
Sediment transfer
Upland
Upland valley
Floodplain valley
Large river
Erosion
Erosion/deposition (aggradation/degradation)
Deposition
from Church 2002

15. Effects of Slope
Steeply sloped rivers will push a flood wave through the watershed more rapidly, creating a higher magnitude event with shorter duration (red hydrograph).
Gently sloped rivers will move a flood wave through the watershed more slowly, creating a lower magnitude event with longer duration (blue hydrograph).

16. Effects of River Length
Shorter rivers will push a flood wave through watershed more rapidly, creating a higher magnitude event with shorter duration (blue hydrograph).
Longer rivers will move a flood wave through watershed more slowly, creating a lower magnitude event with longer duration (red hydrograph).

17. Effects of Roughness
Low roughness rivers will allow a flood wave to travel through river more rapidly, creating a higher magnitude event with shorter duration (blue hydrograph).
High roughness rivers will cause a flood wave to travel through watershed more slowly, creating a lower magnitude event with longer duration (red hydrograph).

18. Material Moved/Deposited by Water
Alluvium
Lacustrine Deposits
Marine Sediments
Beach Deposits

19. Degradation and Aggradation

20. Alluvium Consists of sediment deposited by running water
along many old established streams lie a whole series of alluvial deposits in terraces—young deposits in the normally flooded bottom land of existing streams, up step by step to the very old deposits on highest terraces
remnants of very old stream terraces may be found in dissected country far from any present stream
in some places recent alluvium covers older terraces
typical ridge and swale topography

21. Watershed Geomorphology
River basins can be delineated into three distinct regions with different hydraulic drivers and geomorphic processes
Headwaters (erosion)
Floodplains (aggradation/degradation)
Deltas (deposition)
The Corps continues to study the most economical and environmental suitable methods for using dikes and notching dikes as part of our balancing between our environmental principals and Congressional mandates for navigation and flood control.
Here is a quick, non inclusive list of items that we continue to think about. Do we need to notch every dike? Perhaps un-notched fields provide unique habitat that certain biota need and we would do the river a dis-service to notch every dike.
What is the optimum notch size and shape and location? What types of habitat do different notches produce? Obviously the higher the river stage the less effective the notch becomes so what is the effect of stage on notches.

22. Erosion/deposition (aggradation/degradation)
Sediment Behaviour
Erosion
Long-term storage
Sediment transfer
Upland
Upland valley
Floodplain valley
Large river
Erosion
Erosion/deposition (aggradation/degradation)
Deposition
from Church 2002

23. Hydraulic Processes
It is in those low-gradiant floodplain reaches where we observe dynamic processes such as island and sandbar development and side channel and chute creation due to the continual removal and settling of alluvial material.
Islands, sandbars and paleochannels are not static – alluvium is continually reworked by hydraulic processes and moved downstream, leading to temporal patterns of channel morphology.
The Corps continues to study the most economical and environmental suitable methods for using dikes and notching dikes as part of our balancing between our environmental principals and Congressional mandates for navigation and flood control.
Here is a quick, non inclusive list of items that we continue to think about. Do we need to notch every dike? Perhaps un-notched fields provide unique habitat that certain biota need and we would do the river a dis-service to notch every dike.
What is the optimum notch size and shape and location? What types of habitat do different notches produce? Obviously the higher the river stage the less effective the notch becomes so what is the effect of stage on notches.

24. Wetland Soils
In order to understand wetland soils, we need to know something about:
sediment type/origin
organic material
hydrology/inundation
soil drainage/water flux
biogeochemical redox reactions
soil color

25. Saucier 1974

26. 25 km

28. Floodplain Features
Backwater deposits of fine sediments deposited between natural levees and along valley walls
Terraces are earlier floodplains that may have been formed by river’s alluvial deposits, but are not connected hydrologically with present river (except during high floods)
Low topographic relief deceptive  elevation change of few centimeters may produce quite different hydrologic conditions, soils, and plant communities

29. Ridge and Swale Topography

30. Inundation Classes
Condition that the soil area is covered by liquid free water
Flooding is temporary inundation by flowing (overbank flow) water
If the water is standing, as in a closed depression (precipitation, sheet wash, etc.), the term ponding is used

31. Frequency of Inundation
Classes/Criteria
None (N): No reasonable possibility
Rare (R): 1 to 5 times in 100 years
Occasional (O): 5 to 50 times in 100 years
Frequent (F): > 50 times in 100 years
Common (C): Occasional and frequent can be grouped for certain purposes and called common

32. Duration of Inundation
Classes/Criteria
Extremely Brief (BE): < 4 hours
Very Brief (BV): 4 to 48 hours
Brief (B): 2 to 7 days
Long (L): 7 days to 1 month
Very Long (LV): > 1 month

33. Natural Drainage Classes
Refers to the frequency and duration of wet periods under conditions similar to those under which the soil developed
alteration of the water regime by humans, either through drainage or irrigation, is not a consideration unless the alterations have significantly changed the morphology of soil

34. Natural Drainage Classes
Excessively Drained
water is removed from soil very rapidly
occurrence of internal free water commonly is very rare or very deep
soils are commonly coarse-textured and have very high hydraulic conductivity or are very shallow
Somewhat Excessively Drained
water is removed from the soil rapidly
internal free water occurrence commonly is very rare or very deep
soils are commonly coarse-textured and have high saturated hydraulic conductivity or are very shallow

35. Natural Drainage Classes
Well Drained
water is removed from soil readily but not rapidly
internal free water occurrence commonly is deep or very deep; annual duration is not specified
water is available to plants throughout most of the growing season in humid regions
wetness does not inhibit growth of roots for significant periods during most growing seasons
soils are mainly free of deep or redoximorphic features that are related to wetness

36. Natural Drainage Classes
Moderately Well Drained
water is removed from the soil somewhat slowly during some periods of the year
internal free water occurrence commonly is moderately deep and transitory through permanent
soils are wet for only a short time within the rooting depth during the growing season, but long enough that most mesophytic crops are affected
commonly have a moderately low or lower saturated hydraulic conductivity in a layer within the upper 1 m, periodically receive high rainfall, or both

37. Natural Drainage Classes
Somewhat Poorly Drained
water is removed slowly so that soil is wet at a shallow depth for significant periods during the growing season
occurrence of internal free water commonly is shallow to moderately deep and transitory to permanent
wetness markedly restricts growth of mesophytic crops, unless artificial drainage is provided
soils commonly have one or more of following characteristics: low or very low saturated hydraulic conductivity, a high water table, additional water from seepage, or nearly continuous rainfall

38. Natural Drainage Classes
Poorly Drained
water is removed so slowly that the soil is wet at shallow depths periodically during the growing season or remains wet for long periods
occurrence of internal free water is shallow or very shallow and common or persistent
free water is commonly at or near the surface long enough during the growing season so that most mesophytic crops cannot be grown, unless the soil is artificially drained
the soil, however, is not continuously wet directly below plow-depth
free water at shallow depth is usually present
this water table is commonly the result of low or very low saturated hydraulic conductivity of nearly continuous rainfall, or of a combination of these

39. Natural Drainage Classes
Very Poorly Drained
water is removed from soil so slowly that free water remains at or very near the ground surface during much of the growing season
occurrence of internal free water is very shallow and persistent or permanent
unless soil is artificially drained, most mesophytic crops cannot be grown
soils are commonly level or depressed and frequently ponded
if rainfall is high or nearly continuous, slope gradients may be greater

40. Effects on Wetland Soils
General Hypothesis: Spatial patterns of soil morphology can be explained by hillslope hydrology
well-drained to poorly-drained/water-logged soils
Removals
Additions
Alterations

41. J.C. Bell, U Minn.

42. Organic Material
Accumulates in wet places where it is deposited more rapidly than it decomposes (or is removed)
these deposits are called peat
this peat in turn may become parent material for soils

43. Kinds of Peat According to origin: Sedimentary peat Mossy peat
remains mostly of floating aquatic plants, such as algae, and remains and fecal material of aquatic animals, including coprogenous earth
Mossy peat
remains of mosses, including Sphagnum
Herbaceous peat
remains of sedges, reeds, cattails, and other herbaceous plants
Woody peat
remains of trees, shrubs, and other woody plants

44. Organic Material
Many deposits of organic material are mixtures of peat
Some organic soils formed in alternating layers of different kinds of peat
In places peat is mixed with deposits of mineral alluvium and/or volcanic ash
Some organic soils contain layers that are largely or entirely mineral material

45. Organic Material
In describing organic soils, the material is called peat (fibric) if virtually all of the organic remains are sufficiently fresh and intact to permit identification of plant forms
Called muck (sapric) if virtually all of the material has undergone sufficient decomposition to limit recognition of plant parts
Called mucky peat (hemic) if a significant part of the material can be recognized and a significant part cannot

46. Lacustrine Deposits
Deposits consist of material that has settled out of bodies of still water
unlike ridge and swale topography, ancient lake deposits are generally flat
deposits laid down in fresh-water lakes associated directly with glaciers are commonly included as are other lake deposits, including some of Pleistocene age that are not associated with the continental glaciers
some lake basins in the western United States (playas) have soils that may be more or less salty, depending on climate and drainage

47. Marine Sediments Sediments settled out of the sea
commonly were reworked by currents and tides
later exposed either naturally or following construction of dikes and drainage canals
vary widely in composition; some resemble lacustrine deposits, others more coarse

48. Beach Deposits
Mark the present or former shorelines of the sea or lakes
deposits are low ridges of sorted material and are commonly sandy, gravelly, cobbly, or stony
these ridges are usually above the water table and, hence, generally do not contribute directly to wetland soils
deposits on the beaches of former glacial lakes are usually included with glacial drift

49. Ecosystem Consequences
Soil Texture
coupled with elevation gradients
Biogeochemistry
hydric soils
Vegetation Responses

50. Hydrologic Regime
Floodwaters and subsequent groundwater levels determine type and productivity of vegetation in floodplain
Hydroperiod (flooding duration, intensity, timing) limits plant species composition and influences ecosystem structure and function
import nutrient-rich sediments to floodplain
export organic and inorganic material
timing important  flooding in growing season has greater effect on species survival and ecosystem productivity

51. Vegetation Gradients

52. Riparian Vegetation Zonation
Zone I (open water river corridor)
present day river channel; continuous flooding
Zone II (river swamp forest; deep water alluvial swamps)
have surface water throughout all or most of growing season, but water levels vary seasonally and annually
Zone III (lower hardwood swamp forest; first bottom)
do not stay wet during the entire growing season, nor do they flood every year

54. Vegetation Zonation Zone IV (backwaters or flats; second bottom)
typically has standing water during less than 25% of growing season
Zone V (upper hardwood swamp)
highest elevations of floodplain; encompass natural levees and terraces as well as very old ridges and dunes
only covered with water for very brief periods during growing season, flood no more than 50% of years within a 100-year cycle, and have a water table which is below soil’s surface

55. Vegetation Dynamics Prairie potholes: fluctuating hydrologic regime
dry marsh  regenerating marsh  degenerating marsh  open water  dry marsh
vegetation composed of pronounced concentric rings
length of time wetland holds water  complexity of zonation (number of zones)
water permanence  species richness
Estuaries: salinity gradients: fresh  salt water
corresponding vegetation gradients

56. Prairie Potholes

57. DelawareRiver

58. Salt Marsh Vegetation

59. Other Factors Agricultural disturbances draining grazing/trampling
unless severe  higher species diversity, more complex distribution patterns, sharper boundaries between zones
wind and water erosion
runoff  sedimentation/suspended solids
algal blooms

61. Other Factors Burning common in many wetland ecosystems
removes accumulated litter
releases nutrients
may reduce trapping of snow  local hydrology
impact on species composition variable
(frequency and severity)

63. Summary
Wetland geomorphology (as well as hydrology) extremely important in understanding ecosystem dynamics
Hydrology/hydraulics (directly and indirectly) influences sediment transport, in-stream structure, sediment texture, microtopographic relief, moisture gradients, redox reactions, hydric soils, and vegetation
major consequences for wetland restoration

64. Paul J. DuBowy, Ph.D.
Ecohydrology Associates, LLC
P.O. Box 816
Lovell, Wyoming USA