IMPLICATIONS OF THE ANNUAL MACROPHYTE GROWTH-CYCLE ON HABITAT IN RIVERS

The continuity equation, Manning's equation and an empirically determi ned relationship between channel roughness and the biomass of macrophy tes were used to simulate the effects of weed growth in contrasting ch annels. Two indices of wetted available habitat, velocity and depth we re chosen to illustrate the role of macrophyte in maintaining and modi fying instream habitat with particular reference to chalk streams. Pla nt growth maintained depth within the channels and its effect was modi fied by channel shape and slope. Weed cutting resulted in very sudden changes in depth and velocity and the loss of a large volume of water from the river. The results indicate that macrophyte growth could be u sed to maintain wetted habitat while allowing more abstraction, but mo re data are required on the long-term effects of implementing such pol icies.