Water: WARSSS
Science & TechnologyApplications & DatabasesTechnical ToolsWARSSSHydrologic ProcessesHydrologic Processes
Reconnaissance
Level Assessment
Steps 1. Compile Data
2. Landscape History
3. Critical Activities
4. Process Relations
5. Landscape Overview
6. Hillslope Processes
7. Surface Erosion
8. Mass Erosion
9. Hydrologic Processes
10. Streamflow Changes
11. Channel Processes
12. Impacts
13. Problem Verification
14. Eliminate Non-contributors
15. Further Assessment
Changes in the vegetative cover that influences evapo-transpiration, interception, snow depositional patterns, etc. can change the magnitude, duration and timing of runoff. Urban watershed development can result in a high percentage of impervious surface, that changes the probability, frequency, magnitude and duration of runoff events. The effects of these flow increases can have varying results depending on the morphology (type) of the stream channels and their stability. For example, if streams are incised (G and F) below urban development, then increased flood flows are contained within the channel, causing excess bed and bank erosion, land loss and increased sedimentation. Various stream type delineations are shown in Figures 68 through 70; for review see also Figure 14 (PDF, 192 kb, 1 p.) and Figure 15 (PDF, 168 kb, 1 p.), and Table 3 (PDF, 66 kb, 1 p.) (Rosgen 1994, 1996).
Vegetation and urban changes should be evaluated within second to third order basins to determine potential flow changes. Road density associated with slope steepness needs to be observed by sub-watersheds at this level. This assessment is needed to determine potential change in drainage density due to sub-surface flow interception and change in evapo-transpiration without hydrologic recovery. The potential consequences associated with the processes influenced by an assortment of land uses including streamflow change are shown in Table 9.
Table 9. Relation Between Land Uses/Activities, Processes Influenced, and Consequences
| Activity | Processes Influenced | Potential Consequence | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Streamflow decrease in magnitude, duration and timing. Due to reservoirs, diversions | Shear stress  Stream power Competency Sediment transport capacity |
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| Urban - Stream flow discharge increase due to high % impervious & storm water drains. Clean water discharge | Shear stress Stream power Sediment transport capacity |
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| Stream flow increase from vegetative alteration, clear cutting, land clearing, roads | Shear stress Stream power Magnitude of flow Duration of flows |
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| Riparian vegetation alteration (% of channel length by stream type) | Bank erodibility Sediment transport capacity Stream power Shear stress |
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| Surface disturbances (% of ground cover) and roads |
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| Water yield - harvest & roads - add to soil water influencing slope stability |
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Mass wasting
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| Direct channel impacts channelization levees straightening dredging |
Shear stress Stream power Width Confinement Incision |
Gully erosion Bank erosion Channel enlargement Degradation Aggradation Channel successional state |
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