I am amazed at the sand dam technique.
quite to my astonishment, none of the water engineers I've talked to have ever heard of it, although it's use is widespread in the third world.
I would find it ironic if the advanced first world would end up borrowing a technique pioneered in the third world
A "sand dam" is just a notched weir in a dry river channel that eventually fills with sediment. As long as the ground is relatively impermeable, the weir will store water with or without the sand, more without it actually.
There are good reasons why they only use this desperate method in 3rd world countries. Putting weirs in the LA river (a concrete channel now) or any other flood control channel or dry riverbed would invite disaster by impeding flood flows.
The beaches of So Cal are starved for sand transported from upstream, so this would have unintended environmental consequences - the permit would involve creating a new desert somewhere or some other costly crazy mitigation. Also, the sand would be contaminated with the usual urban stormwater pollution - oil and gas, fertilizer, pesticides, etc. And lastly, how would they film those car chases in the LA aqueduct with all that sand blocking things?
Lots of other ideas Ken posted are great even if the benefits are exaggerated, in my professional opinion. Rain catchments off roofs are widely used in Hawaii and could provide some additional water in SoCal. Groundwater recharge "conjuctive use" is really ramping up but legally dicey (no clear water rights law on how much you can pump out). BTW, leaky pipes are doing just that - recharging the groundwater, so not all that water dripping is "lost", which again means the benefits of patching leaks are overstated. But sediment laden weirs in flood channels? Ain't going happen here.
One of the big problems with most of these ideas is that water comes in big gulps over a few months and then it's dry for 8 months. Storage is the key, and the ground can only absorb so much when it's either paved or saturated. And the biggest problem goes back to that chart I linked to. You'd have to capture every single drop of rain and then cut all urban use in SoCal in half to achieve energy "independence" from outside sources. Do you really see that happening? Keep moving in that direction by all affordable means, but be realistic about it.
