Hydraulic design aspects of rock-weir fishways with notch for habitat connectivity

Abstract

Nature-like fishways have been installed at many migration barriers in recent years to mitigate the effects of human development and habitat fragmentation on fish. The design of these fishways determines the flow characteristics and ultimately the success of these passage facilities. This study numerically investigates the hydraulic properties associated with small passage openings (notch) that are provided in rock-weir-type fishways. Two distinct flow regimes, weir and transitional, were identified. The rock-weir with notch ensured suitable hydraulics for fish migration and sufficient fish resting areas in weir pools. A dimensionless weir coefficient was introduced to existing depth–discharge relationships to compute the weir flow more accurately. A reduction factor for the maximum velocity was also proposed as a function of discharge. This study optimized the design of rock-weir fishways considering passage notches based on fish resting zones, volumetric dissipated power, and performance for upstream fish migration.

Keywords:

• Flow regime
• flow velocity
• fish resting zones
• energy dissipation
• fish swimming performance
• passage notch
• and rock-weir fishway

Acknowledgements

Special thanks to two anonymous reviewers for their constructive comments and suggestions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notation
The following symbols are used in this paper:Agap:	=	area of notch opening,
B:	=	channel width,
Bt:	=	total wetted length of rock-weir crest,
Cd:	=	coefficient of rock-weir discharge,
Cgap:	=	contraction and roughness coefficient,
Cw	=	contraction coefficient for the weir crest profile length,
Df:	=	fish swimming distance,
Dmax:	=	maximum fish swimming distance,
d:	=	height of larger boulders in the rock-weir above channel bed,
E:	=	average volumetric energy dissipation rate,
g:	=	gravitational acceleration,
H:	=	pool averaged water depth along the centre line of the channel,
h:	=	water depth above the rock-weir crest,
Δh:	=	difference in water level between two pools,
K	=	turbulence kinetic energy,
L:	=	pool spacing,
l:	=	height of smaller boulders in the rock-weir above channel bed,
Q:	=	flow rate (m3 s−1),
Qgap:	=	gap flow through the notch,
Qweir:	=	weir flow,
Q*:	=	dimensionless discharge ($Q^{*}=Q/(\sqrt{g{S}_{0}L{B}^{2}dh}$),
$Q_t^{*}$	=	dimensionless discharge at transition $(Q_t^{*}=Q/(\sqrt{(g)}{S}_0{B}_t{L}^{3/2})$ ,
q	=	flow rate per unit channel width
$S_0$	=	channel slope,
T:	=	endurance time,
U:	=	magnitude of flow velocity considering three-directions ($U=\sqrt{u^2+v^2+w^2}$),
Umax:	=	maximum value of U over weir,
Ueq:	=	equivalent average water velocity along the fish path,
Vp:	=	volume of pool excluding the volume of rock-weir,
z:	=	vertical distance from the channel bed,
θ:	=	weir arm angle (plan view angle of departure from bankline),
$\rho$	=	density of water,
µ:	=	weir discharge coefficient,
ε	=	turbulent kinetic energy dissipation rate,
ξ	=	sharp-edged inlet loss coefficient,
a, b, and c:	=	coefficients,

Additional information

Funding

This research is made possible through grants from the Natural Sciences and Engineering Research Council (NSERC) of Canada and Ecofish Research Ltd.