It’s rained so much across California that the state’s biggest reservoirs are filled to levels not seen in years. At least six of the state’s major reservoirs are now holding more than 100% of their historic average, and massive Lake Shasta is so replete with water that dam operators opened spillway channels for the first time in six years this month.   But then there’s thirsty Lake Cachuma. The Santa Barbara County reservoir this week was filled to just 13% of its historical average and 9% of its capacity.