American River Watershed Conference

Watershed Scale Assessment: Geomorphology

Eric M. Ginney, MS

What is Geomorphology?

• Geomorphology attempts to explain features found and processes operating upon the surface of the Earth.

– Sub-types/Special Environments: Hillslope Processes, Fluvial, Coastal, Glacial, & Volcanic

ge·o·mor·phol·o·gy [ jē·ō·mör′fäl·ə·jē ]

Geomorphology in Watershed Assessment:

– Describing the processes that move water, sediment, and organic matter through a watershed.

– Linking the disciplines of hydrology, geology, and ecology with the practice of adaptive management.

Geomorphology in Watershed Assessment is not:

• a list of landforms

•a list of processes

An understanding of how these processes function in a watershed as the underlying foundation for

ecological processes and “human infrastructure benefits.”

Geomorphology in Watershed Assessment is:

•Ecological Processes (and benefits)

Important “Human Infrastructure Benefits” or “Ecosystem Capital” Clean water: Is it Magic?

Is it Magic? No, it’s Geomorphic ProcessErosion Processes: Raindrop impacts, dry ravel, mass failures, wind erosion (aeolian), stream erosion (fluvial)

Sediment Transport Processes:

Colluvial motion, landsliding, debris flows, stream/river transport (fluvial)

Sediment Deposition: on

hillslope, in channel, on floodplain

Rainfall-Runoff

With Roads

Without RoadsQt

time

Volumetric Effect Timing

Effect

Basin Hydrograph

Management and Process Collide: Stream “Diversion Potential” on Roads

Pow!

“Watershed Capture” via Diversion Potential

A Geomorphic Assessment Tool: Sediment Budgets

SourceTransport

Deposition

Sediment Budgeting of:

• Volumes

•Processes

•Rates / Yields (volume/ unit area/ unit time)

(tons/mile2/year)

Adapted from Reid and Dunne, 1996

Conceptual Sediment Budgets

05

101520253035404550

Road-RelatedShallow

Landsliding

RoadSurfaceErosion

HillslopeShallow

Landsliding

DeepSeated

Landsliding

Soil Creep BackgroundHillslopeSurfaceErosion

Hills

lope

Ero

sion

(%)

Selected Results: A Budget for Hillslope Sediment Sources

Another Conceptual Sediment Budget

Adapted from Reid and Dunne, 1996

Transport through River Reaches / Systems

Lessons from Developed (ing) Watersheds

Impervious Surfaces+

Vegetation+

Grading and SoilCompaction

+Construction of drainage

facilities =

Hydromodification is……the change in the runoff hydrograph from an area due

to development.

Altered Hydrograph Processes

Urbanization tends to increase stormwater runoff:

peak flows

volume

frequency

Key Altered Geomorphic Processes

1. Intensifies sediment transport and erosion processes

2. Observed as excessive erosion, incision and widening

Channel Incision

Downstream Deposition

Why? Because of Altered Processes.

Effects on Rivers and Creeks

Questions