CULVERT

Download updated 7 January 2011

It provides biologists and engineers with an integrated solution to some of the more common problems associated with fish passage through culverts and channels.

CULVERT calculates the water velocities flowing through existing or newly designed culverts/channels flowing partially full and determines whether fish passage is possible for common New Zealand fish species. The program models both uniform and non-uniform sub-critical flow and assumes that fish passage is unlikely if flow is super-critical. The programme does not evaluate passage below the culvert outlet or upstream of the inlet.

Programme users are able to model culvert characteristics in order to determine how different conditions may influence fish passage. For example, a user can model the effects of varying gradient or outlet conditions (i.e., the effects of a free outfall compared to a pool). Manning’s N (the index of channel roughness used in the program), is difficult to estimate, especially for low flow conditions. Therefore, when assessing existing culverts, the program allows entry of culvert flow, water velocity and depth to calculate actual values of “N”. With experience, it is anticipated that estimates of “N” in new and existing culverts will become more accurate.

Fish swimming criteria are incorporated in the programme for different fish species. The user is able to alter these criteria to suit. Maximum passage distances are determined for each species of a specific length using relationships between maximum swimming time, fish length, and velocity. These relationships differ between species groups, such as salmonids, eels, and galaxiids. The climbing ability of fish species, such as elvers and koaro, is not taken into account in this programme.