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Watershed Assessment (ENSC 202). Phase 1 – Steps 6-10 Extracted from Vermont ANR Stream Geomorphic Assessment Protocols Handbook - Introduction. Step 6 Floodplain modifications. 6.1 Berms and Roads 6.2 River Corridor Development 6.3 Depositional Features - PowerPoint PPT Presentation
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ENSC 202 – 2004Phase 1 Steps 6-10
Watershed Assessment (ENSC 202)
Phase 1 – Steps 6-10Extracted from Vermont ANR Stream Geomorphic Assessment Protocols
Handbook - Introduction
ENSC 202 – 2004Phase 1 Steps 6-10
Step 6 Floodplain modifications
• 6.1 Berms and Roads• 6.2 River Corridor Development• 6.3 Depositional Features• 6.4 Meander Migration / Channel Avulsion• 6.5 Meander Width Ratio• 6.6 Wavelength Ratio
ENSC 202 – 2004Phase 1 Steps 6-10
Rationale for Step 6
• Streams need floodplains for adjustment
• Development often constrains the floodplain
• Floodplain constraint can increase stream power
• Increased power can move larger particles, leading to degradation
Watershed Input:Sediment Load
Watershed Input:Hydrologic Load
Boundary Condition Channel Geometry
Watershed Input:Sediment Load
Watershed Input:Hydrologic Load
Boundary Condition Channel Geometry
ENSC 202 – 2004Phase 1 Steps 6-10
Step 6.1 Berms and Roads
• Rough percentages in the river corridor
• Does not include crossings• Impact rating
I-89 along Winooski River
ENSC 202 – 2004Phase 1 Steps 6-10
Step 6.2 River Corridor Development
• Houses, fill (including bridge and culvert fills), parking lots or other development
• Impact rating
ENSC 202 – 2004Phase 1 Steps 6-10
Step 6.3 Depositional Features
• Un-vegetated ‘bars’
• Impact rating
ENSC 202 – 2004Phase 1 Steps 6-10
Step 6.4 Meander Migration/Channel Avulsion
• Best done by difference analysis with orthophotos
• GIS or tracing on acetates
• Consider errors in overlays
• Impact rating
High impact migration and avulsion
ENSC 202 – 2004Phase 1 Steps 6-10
Step 6.5 Meander width ratio• Only certain reaches (step 2.10)
– types C or E riffle-pool or ripple-dune reference types– narrow (NW) and unconfined (BD and VB) valleys
• If straighten >50% belt width = channel width MWR=1• naturally confined and braided stream types
– enter “0” for MWR– enter not applicable (“N/A”) for the impact rating
• See Appendix H
ENSC 202 – 2004Phase 1 Steps 6-10
Step 6.6 Wavelength ratio• Same restrictions as in step 6.5• WLR = wavelength/channel width (2.8)
ENSC 202 – 2004Phase 1 Steps 6-10
Step 7 Bed and Bank Windshield Survey
• 7.1 Dominant Bed Form / Material• 7.2 Bank Erosion – Relative Magnitude• 7.3 Debris and Ice Jam Potential
ENSC 202 – 2004Phase 1 Steps 6-10
Rationale & considerations for Step 7
• An opportunity to check validity of Phase 1 assessments before Phase 2 effort
• Do advanced planning to limit drive time• Take care in doing assessments from
bridges bridge impact• Good opportunity to do some photo
documentation
ENSC 202 – 2004Phase 1 Steps 6-10
Step 7.1a Dominant bed form
ENSC 202 – 2004Phase 1 Steps 6-10
Step 7.1b Dominant bed material
ENSC 202 – 2004Phase 1 Steps 6-10
Step 7.2 Bank erosion – relative magnitude
• Bank erosion
• Bank heights
Remember that some erosion is natural
ENSC 202 – 2004Phase 1 Steps 6-10
Step 7.3 Ice/debris dam potential
ENSC 202 – 2004Phase 1 Steps 6-10
Step 8 Stream Impact Ratings
• 8.1 Impact Rating
– High(2), Low(1), Not sig (0), Don’t know (0)
• 8.2 Priority Rating
– A tool available in the database reporting functions
ENSC 202 – 2004Phase 1 Steps 6-10
Step 9 Stream Geomorphic Condition Assessment
• 9.1 Channel Adjustment Process• 9.2 Reach Condition• 9.3 Reach Sensitivity
ENSC 202 – 2004Phase 1 Steps 6-10
Step 9.1 PROVISIONAL channel adjustment processes
This table is generated automatically by the database. See Appendices B and C
Adjustment defined as score > 4
ENSC 202 – 2004Phase 1 Steps 6-10
ENSC 202 – 2004Phase 1 Steps 6-10
Channel Evolution Models (CEM)
• F- and D-stage streams
– unconfined, low gradient valleys where the streams are not entrenched
– access to floodplain at 1-2 year flood stage
• F-stage process: bed and bank is erodible
• D-stage process bed and bank less erodible
ENSC 202 – 2004Phase 1 Steps 6-10
F-stage CEM
ENSC 202 – 2004Phase 1 Steps 6-10
D-stage CEM
ENSC 202 – 2004Phase 1 Steps 6-10
Step 9.2a Reach condition score
• Calculated by the database
• Based on the 4 key adjustment processes
• Calculated for each reach based on the worst adjustment process in the worst reach
• Effectively a ‘bad’ to ‘worst’ scoring system
ENSC 202 – 2004Phase 1 Steps 6-10
Step 9.2b – Reach condition score
ENSC 202 – 2004Phase 1 Steps 6-10
Step 9.3 Reach sensitivity(Subjective)
Considerations
ENSC 202 – 2004Phase 1 Steps 6-10
Step 10 Like Reach Evaluation
• Basically a simple sorting tool in the database
• May help in selecting reaches for Phase 2 field work
ENSC 202 – 2004Phase 1 Steps 6-10
Remember to do your QA/QC!!