Performance of Grass Filters Under Laboratory and Field Conditions

ABSTRACT A design model was demonstrated that estimates the filter effectiveness of grass subjected to sediment-laden runoff. A number of laboratory and field studies indicate that this model possesses the capability of serving as a working tool for estimating the fraction of sediment trapped and outflow concentration as a function of inflow hydraulic and sediment conditions. Additional necessary inputs for the model include the dimensions of the filter and vegetation. Analysis of complex situations, such as where either the channel slope or grass characteristics change along the filter length, is possible. An additional feature of the model is the capability to recalculate particle size distribution as a function of the sediment trapped in the filter. The developed relationships include the terms which would be anticipated to play an important role in filter phenomenon. Evaluation of the model based on verification studies using real grasses in laboratory flumes and in outdoor channels is described. The results from each set of tests indicated that more than 94% of the inflow sediment load was typically accounted for by this design.