VARIABILITY OF SEDIMENT AND SALT LOADS IN THE COLORADO RIVERSIGNIFICANCE FOR CONSERVATION AND MANAGEMENT

THE COLORADO RIVER PROVIDES A VALUABLE WATER RESOURCE TO ALLOR PARTS OF SEVEN WESTERN STATES. DEGRADATION IN THE QUALI-TY OF COLORADO RIVER WATERS (PARTICULARLY SALINITY) WILL HAVE SIGNIFICANT IMPACT ON THE ECONOMICS OF THESE WESTERN STATES AS WELL AS ON THE POLITICAL RELATIONS WITH MEXICO WHICH RECEIVES FLOW FROM THE UNITED STATES. IN THE LATE 19TH CENTURY AND 20TH CENTURY, SEDIMENT AND SALT LOADS IN THE COLORADO RIVER WERE HIGH, HOWEVER, DURING THE 1940'S THERE WAS A DRAMATIC DECREASE IN SEDIMENT DISCHARGE THROUGTHTHE GRAND CANYON AND A DECREASE IN SALINITY AT IMPERIAL DAM IT IS HYPOTHESIZED THAT THE DECREASE IN SEDIMENT LOAD WAS CAUSED BY THE PROGRESSIVE REDUCTION IN EROSION ON RANGELANDSWITHIN THE BASIN DUE TO REDUCTION OF GRAZING AND INCREASED SOIL CONSERVATION TECHNIQUES DURING THE 1920'S AND 1930'S EXPERIMENTAL STUDIES HAVE SHOWN THAT A REDUCTION IN SEDIMENTPRODUCTION FROM THE HEADWATER SLOPES OF A BASIN IS NOT RE- FLECTED AT THE WATERSHED OUTLET UNTIL STORED SEDIMENT HAS BEEN FLUSHED FROM THE CHANNEL NETWORK. IN A SIMILAR MANNER IT COULD BE THAT THE REDUCTION OF SEDIMENT PRODUCTION IN THE COLORADO RIVER BASIN WAS NOT SEEN AS A DECREASE IN SED- IMENT DISCHARGE IN THE COLORADO, GREEN, OR SAN JUAN RIVERS UNTIL STORED ALLUVIUM HAD BEEN REMOVED FROM TRIBUTARY VAL- LEYS. GEOMORPHIC CHANGES IN TRIBUTARY CHANNELS IN THE COLO ADO RIVER BASIN WILL INDICATE WHETHER CHANNEL INCISION AND SEDIMENT'S STORAGE HAS OCCURRED. SITES OF NATURAL SEDIMENT STORAGE WILL ALSO BE SITES OF SALT STORAGE. PROTECTION OF THESE SITES FROM FUTURE REMOBILIZATION THROUGH CHANNEL INCISION AND ARROYO FORMATION MAY PREVENT A REPEAT OCCUR- RENCE OF THE DRAMATIC INCREASE IN SEDIMENT AND SALT LOADS SEEN IN THE 1950S AND 1960S.