Modeling Transport of Subsurface Salinity from a Mancos Shale Hillslope

In the Upper Colorado River Basin, irrigated agriculture is associated with increasing stream salinity. In areas targeted for control of salinity transport to streams, as much as 90% of stream salinity has been estimated to originate from ground water flowing through salt‐bearing stratum. Primary salt sources are the marine shales and the shale residuum that underlie the soils throughout much of the basin. Shallow subsurface flow systems, created by seepage from canals and deep percolation of irrigation water, are believed to be the primary agents leaching the salts from underlying shale deposits and carrying them to streams. This study attempts to determine the relative importance of advective, dispersive, and diffusive salt transport processes from the alluvium covered, shale hillslopes of the region. The results of various irrigation management schemes for appraising the possibility of controlling salt loading to streams are presented.