Predicting Runoff of Water, Sediment, and Nutrients From a New Zealand Grazed Pasture Using CREAMS

Abstract

The ability of the CREAMS model to predict loadings of runoff, sediment and nutrients from a New Zealand grazed pasture was evaluated. Before use, CREAMS was adapted to better represent N and P cycling in grazed pastures and the seasonal variation in hydraulic conductivity observed at the site. There was a moderately strong relationship (r2 = 0.81) between daily surface runoff volumes predicted by this modified model and volumes measured at the site for 62 events over a three and one half year period. Although the ability of the model to predict daily losses of sediment and nutrients was considerably less (r2 < 0.45), the model was always an unbiased predictor. This unbiased predictive ability provides good estimates of losses over longer time scales (e.g., seasonal) which is often sufficient when evaluating the impacts of land use practices on water quality. The adapted CREAMS model successfully simulated measured reductions in edge-of-field losses of sediment and nutrient upon installation of a vegetated filter strip. We conclude that although CREAMS has limitations in representing the dynamics of grazed pastures, it shows potential as a water quality management tool in pastoral watersheds.