Deflector designs for fish habitat restoration

Area of Science:

• Riverine geomorphology
• Instream habitat engineering
• Environmental restoration

Background:

• Paired current deflectors are instream habitat structures used in river restoration to create fish habitat.
• Existing design recommendations for deflectors lack consensus on optimal orientation, height, and length.
• Understanding deflector impacts on channel morphology is crucial for effective restoration.

Purpose of the Study:

• To investigate how deflector angle, height, and length influence scour hole dimensions and bank erosion.
• To evaluate the accuracy of existing scour prediction equations for paired deflectors.

Main Methods:

• Laboratory flume experiments using uniform sand.
• Testing three deflector angles (45°, 90°, 135°).
• Investigating two flow conditions (under and overtopping deflector height) and two length variations (25% and 50% width reduction).

Main Results:

• Deflector angle significantly impacts scour depth, with 45° deflectors causing less scour than 90° or 135° deflectors.
• Flow under the deflector and increased deflector length led to greater scour volume and bank erosion potential.
• Bank erosion potential varied with flow condition and deflector angle; 135° deflectors caused more erosion under flow-under conditions, while 90° deflectors had higher potential during overtopping flow.

Conclusions:

• Deflector design parameters, particularly angle and flow interaction, critically influence scour and bank erosion.
• Existing scour prediction models, like Kuhnle et al., showed reasonable accuracy.
• The assumption that upstream-oriented deflectors consistently cause the most scour requires reevaluation.