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 sal inity 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 res iduum that underlie the soils throughout much of the basin. Shallow su bsurface flow systems, created by seepage from canals and deep percola tion of irrigation water, are believed to be the primary agents leachi ng the salts from underlying shale deposits and carrying them to strea ms. This study attempts to determine the relative importance of advect ive, dispersive, and diffusive salt transport processes from the alluv ium covered, shale hillslopes of the region. The results of various ir rigation management schemes for appraising the possibility of controll ing salt loading to streams are presented.