Flow over weirs with application to fish passage facilities

Riitta Kamula

Department of Process and Environmental Engineering, University of Oulu

Abstract

Fishways are hydraulic structures designed to dissipate the energy of flowing water in order to decrease water velocities and increase water depths. The history of fishways is long, the first written remarks date back to the 17th century. Fishway hydraulics, however, have been intensively studied only starting since the 1980"s. Fishways have been classified into three main categories according to their hydraulic characteristics: pool-and-weir, vertical slot, and Denil fishways. Fishways are hydraulically complex structures, and thus designing tools for different fishway types have been developed. In this report, a new designing procedure has been established, and equations for each main fishway type have been suggested. In addition, flow conditions below different fishway types have been examined, and velocity distributions at weirs with V-shaped crests in both pool-and-weir fishways and at a single weir have been compared in different discharges and drops. Fishway flows have been compared with flows over single weirs.

Table of Contents

Acknowledgements

List of appendices

1. Introduction

1.1. Background
1.2. Studies on fishways in Finland
1.3. Weir flows and fishway flows
1.4. Outline of the thesis

2. Procedures to model fishway flows

2.1. Pool-and-weir fishways
2.2. Denil fishways
2.3. Vertical slot fishways
2.4. Basic concepts for modeling fishway flows

3. Studies on fishway hydraulics

3.1. Studies on pool-and-weir fishways
3.2. Studies on pool-and-weir fishways with a V-shaped crest
3.3. Studies at the water outlet of fish passage models
3.4. Flow over a single V-shaped sharp crested weir

4. Fishway flows

4.1. Flow characteristics in fishway flows

4.2. Scaling factor for fishway flows

4.3. The dimensionless discharge equation for fishways

4.4. Evaluation and applicability of the procedure

4.4.1. Evaluation of the procedure
4.4.2. Applicability to the flows in pool-and-weir fishways
4.4.3. Applicability to the flows in Denil fishways
4.4.4. Applicability for the flows in vertical slot fishways

4.5. Dimensionless discharge equations for the main fishway types

4.6. A practical example of application

5. Hydraulic conditions at the water outlet of fish passage facilities

5.1. Considerations of the scaling factors
5.2. Velocity distribution below different fishway types
5.3. Flow conditions below fishway entrances

6. Velocity distribution at v-shaped sharp crested weirs

6.1. Scaling factor for velocities
6.2. A single V-shaped sharp crested weir
6.3. The flow over a chain of V-shaped sharp crested weirs
6.4. Considerations of the velocity distribution at V-shaped sharp crested weirs

7. Discussion

7.1. Flow over weirs
7.2. Procedure for modeling flows in fishways
7.3. Flow below fishways
7.4. Velocity distribution at a weir with a V-shaped crest

1. Fishway scale model studies at the University of Oulu during 1991-1995

2. Pool and weir fishways – studies at the University of Alberta, Canada

3. Denil fishways – studies at the University of Alberta, Canada

4. Vertical slot fishways – studies at the University of Alberta, Canada

5. Fish and boat pass channel – studies at the Public Works Research Institute, Japan

6. Pool -type fishway with V-shaped overfalls– studies at the Delft Hydraulics and Agricultural University, Netherlands

7. Experimental observations, computed discharges and statistical parameters

List of Tables
1. Computation of statistical parameters of the Student’s t-test of the general procedure using equation 22 for scaling discharges and pool length L as a length scale.
2. The comparison of the scaling factors and dimensionless equations created according to them.
3. Computation of statistical parameters of the Student’s t-test of the general procedure using equation 5 for scaling discharges and opening width b_oas a length scale.
4. Computation of statistical parameters of the Student’s t-test for pool-and-weir fishways using equation 22 for scaling discharges and pool length L as a length scale.
5. Computation of statistical parameters of the Student’s t-test for Denil fishways using equation 22 for scaling discharges and pool length L as a length scale.
6. Computation of statistical parameters of the Student’s t-test for vertical slot fishways using equation (22) for scaling discharges and pool length L as a length scale.
7. Suggested dimensionless discharge equations for different fishway types with Equation (22) used for scaling discharges and the distance between the weirs used for scaling lengths.

List of Figures
1. A sketch of pool-and-weir fishways (modified from Katopodis 1992).
2. Plunging and streaming flows in pool-and-weir fishways (Clay 1961).
3. Definition sketches for a) plunging flow and b) streaming flow (redrawn from Rajaratnam et al. 1988).
4. A schematic representation of a plain Denil fishway with definitions for dimensions. For standard design, B = 0.56 m, b = 0.36 m, a = 0.25 m, k = k’ = 0.13 m and ψ = 45°.
5. The simplest, yet effective, vertical slot fishway design (according to Rajaratnam et al. 1992).
6. Uniform flow in a fishway.
7. A model of a pool-and-weir fishway at Water Resources and Environmental Engineering Laboratory.
8. Study arrangements for pool-and-weir fishways.
9. The fishway modeling flume at the T. Blench Hydraulic Laboratory.
10. Study arrangements for studies on fishways with V-shaped sharp-crested weirs.
11. Study arrangements for the studies on velocity distribution at the V-shaped sharp-crested weir.
12. The pool-and-weir fishway element with a V-shaped crest inside the flume in the studies for the hydraulic conditions at the outlet of fishway types.
13. Element dimensions for the studies on the flow below the a) pool-and-weir fishway, b) pool-and-weir fishway with a V-shaped crest, c) vertical slot fishway, and d) Denil fishway.
14. The single V-shaped sharp-crested weir at the Water Resources and Environmental Engineering Laboratory.
15. Study arrangements for studies on a single V-shaped sharp-crested weir.
16. Definition sketch for uniform flow.
17. Calculated dimensionless discharges Q* plotted against dimensionless water depths y_o/L and regression power lines of author’s data when equation (20) is used for scaling.
18. Recalculated dimensionless discharges Q* plotted against dimensionless water depths y_o/L and regression power lines when equation (20) is used for scaling discharges.
19. Fitting curve for the previously developed scaling factor (Eq. 5) for dimensionless discharges.
20. Upper water level and water depth at the weir, measured from the bottom in a pool-and-weir fishway model (S_o=10%).
21. Definition sketch for studies at the fishway entrance.
22. Flow below fishway entrances visualized by dye for a) pool-and-weir with low flow, b) pool-and-weir with high flow, c) pool-and-weir with a V-shaped crest with low flow, d) pool-and-weir with a V-shaped crest with high flow, e) vertical slot, and f) Denil fishway. Flow direction is from left to right.
23. Velocity distribution at the mid-axis below fishway entrances for a) pool-and-weir with low flow, b) pool-and-weir with high flow, c) pool-and-weir with a V-shaped crest with low flow, d) ) pool-and-weir with V-shaped crest with high flow, e) vertical slot, and f) Denil fishway. Flow direction is from left to right. V is the mean velocity at the cross section, y is the water depth from the bottom, Y is the total water depth at the tailrace, and x is the distance from the fishway outlet. Q is the discharge in the model.
24. Definition sketch for studies on a separate V-shaped weir.
25. Dimensionless velocities at a single V-shaped sharp-crested weir for different heads Δh and discharges Q.
26. Dimensionless velocities v* at the V-shaped sharp-crested weir of a pool-and-weir fishway with different pool lengths L and dimensionless discharges Q*.
27. Typical velocity profiles at the weir of a pool-and-weir fishway. y is the water depth measured from the bottom of the V-notch and d is the water depth perpendicular to the bottom (redrawn from Katopodis 1995).
28. Velocity distribution at a weir for a pool-and-weir fishway with a V-shaped crest at a flow of 2 m3/s. Velocities in m/s (redrawn from Boiten 1990).
29. Dimensionless velocity distribution at the mid-axis of a pool-and-weir fishway with a V-shaped weir.
30. Centerplane velocity vector plots for a Denil fishway with large baffle spacing (Katopodis et al. 1997).
31. Velocity profiles for Denil fishways for slopes of a) 10 %, b) 20 % and c) 30 % (Katopodis 1995).
32. Different nappe types (Lakshamana Rao 1975).
33. Regimes of flow for rectangular sharp-crested weirs a) impinging jet, b) breaking waves, c) surface wave, d) surface jet (Wu & Rajaratnam 1996).
34. Definition sketch for flow below a deeply submerged rectangular weir; a general view of the flow (from Rajaratnam & Muralidhar 1969).
A1.1. Fishway modeling flume at the Hydraulic and Water Resources Engineering Laboratory (Photo Antti Aitto-oja).
A1.2. Study arrangements and water circulation: 1) collection tank, 2) equalizing flume, 3) head tank, 4) tail tank (Kamula and Bärthel 2000).
A1.3. The vertical slot fishway types studied.
A1.4. The stilling basin structures tested. Measuring lines are marked with dashed lines.
A1.5. The dimensions of the baffles for the model studies of Denil fishways (Kamula and Bärthel 2000).
A2.1. Definition sketches for a) plunging flow and b) streaming flow.
A3.1. A set of the studied designs with design dimensions (Katopodis 1992).
A4.1. Vertical slot fishway design layouts including circulation patterns in the pools (Katopodis 1992).
A5.1. Schematic drawings of Models 1, 2, 3, 4, and 5 of fish and boat pass channel.
A6.1. Layout of the V-shaped pool fishway (Boiten 1990b).

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