You need to address the reason why they're empty. You said you know the system well, so do you mind explaining?
On top of that, that ‘useful’ could have been very limited. For example, shortening a half year drought by a week would not be worth anything if it just meant crops would die a week later.
You have to do some serious modeling on expected rainfall, the costs of reservoirs and water usage to figure out whether additional reservoirs are worth the investment.
It has been years since some of the large reservoirs were close to full. Where specifically do you believe new reservoirs should be built? And why do you do believe that they will capture water that keep from evaporating long enough to make a difference during the next drought cycle?
As it stands California’s reservoirs never seem to fill completely anymore. Adding more reservoirs won’t help store extra water if it simply isn’t falling from the sky.
You should not stop all the water from reaching the ocean in the first place, bad things happen when you do that. We are reaching the point where we just have enough water to keep the rivers flowing so we don't kill all the wildlife that exists in them, we're not adding significant amounts of water to storage.
We're storing a teeny tiny fraction of all the water that goes through the system.
One is you want to keep the rivers flowing in the first place. If you impound too much water, you don't have rivers, you have dry creeks and all the wildlife in them dies.
The big one is water rights. The water is not the states to impound in the first place in many cases. If I have particular water rights, and you block them, I can sue you out of existence under existing laws, laws that are going to be very hard to break with our current legal system.
That's only if we build massive dammed reservoirs that try to serve dense populations from a single source like Hetch Hetchy supplying the Bay Area. A system of smaller reservoirs dotted across the state would serve the same function without the concentrated ecological impact. San Francisco has three terminal reservoirs within its city limits, for example.
> The big one is water rights. The water is not the states to impound in the first place in many cases. If I have particular water rights, and you block them, I can sue you out of existence under existing laws, laws that are going to be very hard to break with our current legal system.
That's why utilizing the whole water cycle is important, rather than concentrated sources like rivers and streams. A farmer can prove you're taking his inch of water by comparing upstream of the installation but it's much harder to do that if snowmelt is being collected in hundreds of smaller reservoirs along the mountains. (IANAL, so grain of salt and all that)
A serious question? More water in reserve = more water in reserve.
If you fill 4 glasses with water now, and then then EBMUD turns the water off for the rest of the day due to a broken main (I know EBMUD really well), you'll have 4 more glasses of water to drink than you would have, otherwise. Simple math, really.