Sand-storage changes in the Colorado River downstream from the Paria and Little Colorado rivers, April 1994 to August 1995

Abstract

Sixty-six cross sections on the Colorado River in 11-kilometer reachesdownstream from the Paria and Little Colorado Rivers were monitoredfrom June 1992 to August 1995 to provide data to evaluate the effectof releases from Glen Canyon Dam on channel-sand storage and fordevelopment of multidimensional flow and sediment-transport models.Most of the network of monumented cross sections was established andfirst measured JuneSeptember 1992. Data collected from June 1992through February 1994 were published in a previous report. Crosssections downstream from the Paria River were remeasured six timesbetween April 1994 and August 1995. Most sections downstream from theLittle Colorado River were remeasured four times in the same timeperiod. Each measurement consisted of 10 passes across the section,and data presented are the mean section and the standard deviationfrom the mean. Measured depths were converted to bed elevations usingwater-surface elevations measured or estimated for each reach. A linemarked at regular intervals was strung across the river between thesection end points and used to provide horizontal-position control. AWilcoxon rank-sum test was applied to the data, and bed-elevationdifferences between successive measurements that were statisticallysignificant at the 5-percent significance level were identified andused to compute the difference in cross-sectional area frommeasurement to measurement. Changes in sand storage computed forselected cross sections are presented. Changes in area at most of theselected cross sections during the period presented in this reportwere smaller than those measured during the period covered bythe previous report. The largest changes over the monitoring periodpresented in this report were measured at section p22 (+115 squaremeters) downstream from the Paria River and at sections lb1 (+209square meters) and lc2 (156 square meters) downstream from theLittle Colorado River. This report presents selected data from themeasurements made from April 1994 through August 1995 in graphicalform and describes the electronic form of the entire data set.