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!!