Abstract
Salmonid spawning habitat restoration projects have been an effective method of mitigating the negative effects of anthropogenic influence on the Lower American River, Near Sacramento, California. Embryonic mortality rates of salmonid species are greatly affected by gravel permeability and grain size distributions within the host gravel. The goal of this research is to further understand how the composition of the hyporheic river gravels affects permeability. Using Sodium-Chloride tracers, standpipe drawdown tests and bulk samples, relationships were analyzed between measured seepage velocities and grain size distribution. These statistics include mean grain size, sorting, skewness and kurtosis. Measurements were recorded at approximately 30cm depth in the gravel, where salmonid species typically lay their eggs. Results of permeability measurements and grain size distributions were compared in both restored and un-restored spawning gravels. A clear relationship exists between the sorting (Standard Deviation) of gain size population and the seepage velocity. As restoration sites age seepage velocities degrade and become more unpredictable. Variability of seepage velocities with respect to grain sorting is the result of other factors such as grain orientation and packing, which influence permeability by control porosity. In this respect, permeability may be used as a proxy for the relative health of a particular spawning site.