MODELING THE EFFECTS OF LAND-USE CHANGE ON THE WATER TEMPERATURE IN UNREGULATED URBAN STREAMS

Streams, in their natural state, are typically diverse and biologicall y productive environments. Streams subject to urbanization often exper ience degradation brought about by the cumulative effects of flow alte ration, unsanitary discharge and channelization. One of the water qual ity parameters affected by urbanization is stream temperature. This st udy offers a model for predicting the impact of land use change on the temperature of non-regulated streams during extreme events. A stream temperature model was created by considering the gains and losses of t hermal energy resulting from radiation, convection, conduction, evapor ation and advection. A sensitivity analysis showed that out of 14 vari ables, shade/transmissivity of riparian vegetation, groundwater discha rge, and stream width had the greatest influence on stream temperature . These same three variables are highly influenced by land use. Indivi dual component models were developed to predict how urbanization chang es stream width and baseflow discharge. Using 3-D computer modeling, a model was also developed to illustrate the effects of altering the ex tent and composition of riparian vegetation on streams with different orientations. By modeling these three variables as a function of urban ization, the results became inputs into the stream temperature model. The critical urban stream temperature model (CrUSTe), an aggregation o f these four models, allows the prediction of stream temperature chang e as a result of amount, type and location of urbanization within a wa tershed. It has the potential to become a valuable tool for environmen tal managers. (C) 1997 Academic Press Limited.