Guidance for Design Hydrology for Stream Restoration and Channel Stability (2017) / Chapter Skim
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2C h a p t e r 2 2.1 Overview of the Design Hydrology Process There are two primary phases to the design hydrology for stream restoration and channel stability at stream crossings (hereafter "design hydrology") process: • Phase 1: Assess the Current Conditions Adjacent to the Stream Crossing and in the Watershed to Determine Design Effort.
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the Design hydrology process 3 2.3 Phase 1: Assess the Current Conditions Adjacent to the Stream Crossing and in the Watershed to Determine Design Effort Both Phases 1 and 2 can be related to the overall decision table found in Figure 2-1. Phase 1 is the process of relating stream response potential (SRP)
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4 Guidelines for Design hydrology for Stream restoration and Channel Stability 2.3.2 v* Versus Flashiness A fundamental physical relationship that is missing from Table 2-1 is a ratio of flow energy relative to boundary material resistance.
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the Design hydrology process 5 G = specific gravity of sediment (2.65 is typically assumed) ; and D50 = median grain diameter of the bed material [m]
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6 Guidelines for Design Hydrology for Stream Restoration and Channel Stability exhibiting the early off-ramp conditions would warrant examination of the secondary factors. For example, a stream bed dominated by medium to coarse gravels could be as sensitive as a very high risk category if its banks were weak (alluvium lacking vegetation)
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the Design hydrology process 7 domain for conducting the RGA should be at least 20 channel widths upstream and downstream in accordance with the recent Caltrans (2015) guidance.
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8 Guidelines for Design hydrology for Stream restoration and Channel Stability Table 2-3 are required to be met. If the analyst is unable to find an appropriate analog reach with a similar drainage area, similar channel type, and similar hydrology and that is stable, then exclusive reliance on an analytical design method is recommended.
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Flow/ Sediment Regime Alterations Are there any noteworthy tributaries, dams, or intervening flow augmentations or extractions? No Tributaries, dams, and flow augmentations or extractions can initiate changes in the flow and sediment regimes.
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10 Guidelines for Design hydrology for Stream restoration and Channel Stability from the RGA analysis to select the most appropriate combination of analyses (Figure 2-1) and transition to Phase 2: Design the Stream Channel Through the Stream Crossing.
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the Design hydrology process 11 When selecting the sediment supply reach, the designer should use the reach or subreach that is most representative for sediment continuity. Avoid scour areas immediately downstream of headcuts or hardpoints, as well as aggradational areas immediately upstream of hardpoints.
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12 Guidelines for Design hydrology for Stream restoration and Channel Stability Is the site gaged? Yes No No No Yes Yes Is the gage record stationary?
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the Design hydrology process 13 future flow regimes that result from land use change. If hydrology is non-stationary, scenario analysis that examines sediment and water continuity of both near bankfull and overbank flood flows under both current and potential future hydrologic conditions [e.g., Soil and Water Assessment Tool -- channel DEGradation (SWAT-DEG)
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