Impacts of vegetative practices on suspended sediment from watersheds of Arizona

Effects of vegetative practices on suspended sediment discharge from ponder osa pine forests and pinon-juniper woodlands in north-central Arizona are e xamined. Sediment-rating curves were developed to analyze the impacts. Dist urbance from vegetative practices generally increased suspended sediment tr ansport above those of control (reference) watersheds. Completely cleared a nd strip-cut ponderosa pine watersheds produced higher sediment concentrati ons than did a control watershed. Likewise, cabled and herbicide-treated pi non-juniper watersheds yielded higher sediment-laden streamflows than did a control. Sediment transport regimes are also related to streamflow-generat ion mechanisms and hydrograph stages. Although about 85% of the data analyz ed represented snowmelt-runoff events in both vegetative types, derivation of sediment-rating curves based on streamflow-generation mechanisms improve d the sensitivity of the analysis. Sediment data collected during rising an d falling hydrograph stages varied between the two vegetative types. Sedime nt concentrations were generally higher in the rising stage than in the fal ling stage for ponderosa pine watersheds. There was no clear evidence of hi gher sediment concentrations in the rising stage of the hydrograph as compa red to the falling stage in the pinon-juniper watersheds.