干旱区生态环境知识资源中心

A quantitative study on fluvial processes was carried out in an upland stream catchment (9.3 ha) near Agolai in the NE of Jodhpur district in the Thar Desert in Rajasthan. The catchment of the studied second order ephemeral channel (1.0-1.4 km long and 1.0-1.5 m deep) has developed on a hill - rocky/gravelly pediment - colluvial plain sequence on rhyolite. Initial results of measurements of channel parameters during two significant runoff generating events of 42 mm and 52 mm in 2007 showed peak discharges of 20 m(3)s(-1) (upstream) and 13 m(3)s(-1) (downstream) that moved sediments (bedload) to distances of 43 m - 141 m in the upstream reach, 6-28 m in the middle reach and 63-95 m in the lower reach. The long profile and cross profile measurements showed a balance between load and discharge through a sequence of alternate deposition and erosion throughout the channel. Hypsometry curves revealed maximum erosion (7.7 cm) in the upper reach and aggradation (2.90 cm) in the lower reach. Cross profile measurements showed bank cuts (6 cm) and vertical incisions (1-2 cm) on the rocky-gravelly V shaped valley in the upper reach, incision (4-30 cm) and localized higher deposition (10-12 cm) in the narrow (< 1m) and deep (> 1m) U shaped valleys in middle reach and mainly deposition (13 cm) on the wide ( 1-4 m) and shallow channels (0.1 to 0.2 m) in the lower reach.