Cal. Sts. & Hy. Code § 831
Whenever real property within a public water district is acquired for state highway purposes on or after the effective date of this section, the director shall calculate an amount of severance aid as provided in this section, in addition to any other allowances provided by law to be paid to the district.
For the five-year period following the acquisition of such property, based on the amount of tax revenues the district would have received from such property if there had been no such acquisition, the director shall calculate the district's severance aid as follows: for the year following such acquisition, the district shall be allowed the amount of tax revenues that would have been paid during the year of acquisition, if the taxes assessed on the property acquired were then paid in full; for the second year, the district shall be allowed 80 percent of such amount; for the third year, the district shall be allowed 60 percent of such amount; for the fourth year, the district shall be allowed 40 percent of such amount; and for the fifth year, the district shall be allowed 20 percent of such amount.
Ca. Sts. and High. Code § 831