Sand dams, a water harvesting system built in arid or semi-arid regions,
collect and store water in saturated sands to increase water
availability in dry seasons, while avoiding evaporation and reducing
water-borne disease vectors. The capacity of the dam to store water
depends on the texture of the sediment accumulated in the reservoir. An
ideal sand dam is expected to wash fine-grained particles, especially
silt and clay out of the reservoir, collecting only coarse particles to
provide for maximum open pore space and minimum capillary retention (the
water is typically extracted via an open well). Although conceptually
simple, sand dam commonly failed due to the retention of fine particles.
It has been recommended to build sand dams in stages to overcome this
problem, with each stage low enough so that the shear forces of flow
will keep silt and clay mobile, and pass them out of the reservoir.
Although it is effective, this method is not preferred in terms of cost
and time spent (repeatedly re-mobilizing a team to add to the dam). We
present a new approach to the siltation problem by seeking an ideal
shape (weir) cut in the face of a sand dam designed to provide shear
forces such that coarse particles accumulation while washing the finer
materials such as silt and clay. This will be done by finding a relation
between the cut-outs of in the face of the dam and the sediment
transport rates. Challenges in predicting sediment transport rate are
investigated using both numerical and experimental modeling. We seek to
reduce the failure rate of sand dams, and also provide for a method to
re-establish sediment fills behind existing dams.