Fluvial Geomorphology Prof. Dr. Paul J. DuBowy Ecohydrology Associates, LLC Lovell, Wyoming 82431 USA ecohydrology.associates@gmail.com

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

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.

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.

Macro- to Micro-geomorphology FISRWG

Cross-section

Channel Morphology

Stream Morphology

Sinuosity

Slope Calculations

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

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

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).

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).

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).

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

Degradation and Aggradation

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

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.

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

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.

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

Saucier 1974

25 km

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

Ridge and Swale Topography

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

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

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

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

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

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

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

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

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

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

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

J.C. Bell, U Minn.

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

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

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

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

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

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

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

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

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

Vegetation Gradients

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

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

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

Prairie Potholes

DelawareRiver

Salt Marsh Vegetation

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

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)

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

Paul J. DuBowy, Ph.D. Ecohydrology Associates, LLC P.O. Box 816 Lovell, Wyoming 82431 USA ecohydrology.associates@gmail.com