Sediment yield exceeds sediment production in arid region drainage basins

We use Be-10 and Al-26 to determine long-term sediment generation rates, id entify significant sediment sources, and test for landscape steady state in Nahal Yael, an extensively studied, hyperarid drainage basin in southern I srael. Comparing a 33 yr sediment budget with 33 paired Be-10 and Al-26 ana lyses indicates that short-term sediment yield (113-138 t.km(-2).yr(-1)) ex ceeds long-term sediment production (74 +/- 16t.km(-2).yr(-1)) by 53%-86%. The difference suggests that the basin is not in steady state, but is curre ntly evacuating sediment accumulated during periods of more rapid sediment generation and lower sediment yield. Nuclide data indicate that (1) sedimen t leaving the basin is derived primarily from hillslope colluvium, (2) bedr ock weathers more rapidly beneath a cover of colluvium than when exposed, a nd (3) long-term erosion rates of granite, schist, and amphibolite are simi lar.