ENSC 202

1
Watershed Assessment (ENSC 202)

• Phase 2 Step 6
• The Rapid Habitat Assessment (RHA)
• Extracted from Vermont ANR Stream Geomorphic
  Assessment Protocols Handbook - Introduction

2
Objectives of the RHA

• Determine if a stream is supporting or not
  supporting aquatic life
• Characterize the existence and severity of
  impairment
• Help to identify sources and causes of impairment
• Evaluate the effectiveness of control actions and
  restoration activities

3
High vs Low Gradient Streams

• High gradient streams typically appear as steep
  cascading streams, step/pool streams, or streams
  that exhibit riffle/pool sequences (usually
  stream types A, B, and C). Most of the streams
  (outside of Chittenden County!) in Vermont are
  high gradient streams.
• Low gradient streams typically appear slow moving
  and sinuous, and have less clearly defined
  riffles and pools and may even exhibit
  ripple-dune bed features (usually stream types E
  and sometimes C). Common in valley bottoms of
  the Champlain Valley.
• Most of our stream reaches will be low gradient

4
RHA 1 Epifaunal Substrate / Available Cover
Reference condition
Poor condition

• Keys
• Quantity
• Variety

5
RHA 2 Embeddedness Pool Substrate
Characterization
Reference condition
Poor condition
Focus on riffles
High Gradient

• Keys
• Type
• Variety

Low Gradient
6
RHA 3 Velocity/Depth PatternsPool Variability
Reference condition
Poor condition
High Gradient
Low Gradient
7
RHA 3 Criteria
Slow Fast
Deep D gt 1.5 feet (0.5 m) V lt 1 ft/sec (0.3 m/sec D gt 1.5 feet (0.5 m) V gt 1 ft/sec (0.3 m/sec
Shallow D lt1.5 feet (0.5 m) V lt 1 ft/sec (0.3 m/sec D lt 1.5 feet (0.5 m) V gt 1 ft/sec (0.3 m/sec

• Bed Features
• Step
• Riffle
• Run
• Pool
• Glide

High Gradient
Small Large
Deep WL lt ½ Wbkf D gt 3 feet WL gt ½ Wbkf D gt 3 feet
Shallow WL lt ½ Wbkf D lt 3 feet WL gt ½ Wbkf D lt 3 feet

• Keys
• Even mix
• Deep pools

Low Gradient
8
RHA 4 Sediment Deposition
Poor condition
Reference condition

• Keys
• Point bars
• Mid-channel bars
• Islands
• Some of these are natural!

9
RHA 5 Channel Flow Status
Reference condition
Poor condition

• Typical flow alterations
• hydropower
• irrigation
• public water supplies
• snowmaking
• recreation and flood control reservoirs

10
RHA 6 Channel Alteration
Reference condition
Poor condition

• Keys
• Berms
• Dredging
• Straightening
• Armoring (revetments)

11
RHA 7 Morphological DiversitySinuosity
Reference condition
Poor condition
High Gradient
Low Gradient
12
RHA 8 Bank Stability
Reference condition
Poor condition
13
RHA 9 Bank Vegetation Protection
Reference condition
Poor condition

• Keys
• Root binding capacity
• Grass no good for banks gt 0.5 m (1.5 ft)
• Shrubs/trees no good for banks gt 1.5 m (4.5 ft)

14
RHA 10 Riparian Buffer Width
15
RHA Score
RHA S(individual scores)/200