Compost is a recycled material and has been shown to remove various pollutants from runoff water. Increased use of compost will also reduce the solid waste sent to landfills. This research is part of a larger study designed to develop compost buffers (i.e., an unsupported mound of compost that intercepts surface runoff from a site) suitable for removing nutrients and sediment from agricultural operations in southern California. The goal of this study is to evaluate the behavior of compost buffers with different masses and particle size distributions when subject to varying water flow rates. In this study, we identify the maximum flow rate that compost buffers can sustain before a structural failure occurs (ranging from 0.8 to 4.0 l/s/m). Based on this maximum flow rate and physical properties of the buffers, we quantify the range of the coefficient of static friction (ranging from 0.20 to 0.88). With these data, a model is developed and presented to predict headloss through a compost buffer as a function of the flow rate per unit width, the median particle size of the compost media, and the buffer dimensions. We quantify the effect that a given sediment concentration has on the headloss of a buffer (percentage of sediment removal ranges from 5 to 35%), and finally we identify the range of the hydraulic conductivity (ranging from 5 to 110 cm/s) and the intrinsic permeability (ranging from 0.00006 to 0.002 cm2) as a function of the flow rates, the flowing media properties (water) and the porous media properties (compost).