Sediment yield exceeds sediment production in arid region drainage basins

We use ¹⁰ Be and ²⁶ Al to determine long-term sediment generation rates, identify significant sediment sources, and test for landscape steady state in Nahal Yael, an extensively studied, hyperarid drainage basin in southern Israel. Comparing a 33 yr sediment budget with 33 paired ¹⁰ Be and ²⁶ Al analyses indicates that short-term sediment yield (113-138 t · km ^-2 · yr ^-1 ) exceeds long-term sediment production (74 ± 16 t · km ^-2 · yr ^-1 ) by 53%-86%. The difference suggests that the basin is not in steady state, but is currently evacuating sediment accumulated during periods of more rapid sediment generation and lower sediment yield. Nuclide data indicate that (1) sediment leaving the basin is derived primarily from hillslope colluvium, (2) bedrock weathers more rapidly beneath a cover of colluvium than when exposed, and (3) long-term erosion rates of granite, schist, and amphibolite are similar.