ENSC 202 – 2004Phase 2 Step 6 RHA

Watershed Assessment (ENSC 202)

Phase 2 – Step 6The Rapid Habitat Assessment (RHA)

Extracted from Vermont ANR Stream Geomorphic Assessment Protocols

Handbook - Introduction

ENSC 202 – 2004Phase 2 Step 6 RHA

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

ENSC 202 – 2004Phase 2 Step 6 RHA

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

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 1 – Epifaunal Substrate / Available Cover

Reference condition Poor condition

Keys• Quantity• Variety

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 2 – Embeddedness Pool Substrate CharacterizationReference condition Poor condition

HighGradient

LowGradient

Focus on riffles

Keys• Type• Variety

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 3 Velocity/Depth PatternsPool Variability

Reference condition Poor condition

HighGradient

LowGradient

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 3 Criteria

Slow Fast

Deep D > 1.5 feet (0.5 m)

V < 1 ft/sec (0.3 m/sec

D > 1.5 feet (0.5 m)

V > 1 ft/sec (0.3 m/sec

Shallow D <1.5 feet (0.5 m)

V < 1 ft/sec (0.3 m/sec

D < 1.5 feet (0.5 m)

V > 1 ft/sec (0.3 m/sec

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

Small Large

Deep W&L < ½ Wbkf

D > 3 feet

W&L > ½ Wbkf

D > 3 feet

Shallow W&L < ½ Wbkf

D < 3 feet

W&L > ½ Wbkf

D < 3 feet

HighGradient

LowGradient

Keys• Even mix• Deep pools

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 4 Sediment Deposition

Reference condition Poor condition

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

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 5 Channel Flow StatusReference condition Poor condition

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

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 6 Channel AlterationReference condition Poor condition

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

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 7 Morphological DiversitySinuosity

Reference condition Poor condition

HighGradient

LowGradient

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 8 Bank Stability

Reference condition Poor condition

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 9 Bank Vegetation Protection

Reference condition Poor condition

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

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA 10 Riparian Buffer Width

ENSC 202 – 2004Phase 2 Step 6 RHA

RHA Score

RHA = Σ(individual scores)/200