CM (g) REASONABLE CARRYOVER Hearing officer guidelines for calculations In determining a reasonable amount of carry-over storage water, the Director shall consider the average annual rate of fill of storage reservoirs and the average annual carry-over for prior comparable water conditions and the projected water supply for the system. Recommended Order at 51 Use sufficient number of years to encompass wet and dry years Begin with year Palisades was fully operational Include years when the effect of groundwater pumping was minimal Summarized from : Recommended Order at 51

Proposed protocol for establishing basis of reasonable carryover Develop statistical model for each SWC canal of historic climate and water supply data with historic carryover Irrigations years 1964 through 1986 can be used to establish historic carryover relation when ground water pumping effects were minimal and after Palisades was built. Use statistical model to estimate current carryover as if ground water pumping effects were absent Substitute current climate and water supply data for historic values in model REASONABLE CARRYOVER

CARRYOVER = 337, ALLOC HEISE100AF + 4,622 PDSI – 12,336 ETR Where: ALLOC = storage allocation for year in acre-feet, HEISE100AF = Heise April through July runoff volume in 100 acre-feet, PDSI = September Palmer Drought Severity index, and ETR = Seasonal potential crop evapotranspiration in inches, calculated with Twin Falls WSO temperature, NASS crop distribution for region, and average crop coefficient. TWIN FALLS CANAL COMPANY STATISTICAL MODEL

R-Square = 81.1% TWIN FALLS CANAL COMPANY STATISTICAL MODEL

TWIN FALLS CANAL COMPANY 2002 example 2001 reasonable carryover calculated at end of season using these values from the 2001 season in equation: Storage Allocation = 209,758 acre-feet April – July Heise runoff = 1,659 acre-feet * 100 September PDSI = ETR = inches CARRYOVER = 337, * 209, * 1, ,622 *(-5.5) – 12,336 * CARRYOVER = 18,000 acre-feet (rounding)

TWIN FALLS CANAL COMPANY 2002 example 2001 actual carryover: 10,000 acre-feet (rounding) Difference between actual and calculated reasonable amounts: 18, ,000 8,000 (Reasonable Carryover Deficit) If reservoir storage accounts do not fill in 2002 and the difference between baseline demand and forecasted supply exceeds the reasonable carryover deficit, then this amount, or portion thereof needed to meet a demand shortfall, is due two weeks after storage allocations are made by Water District 01.

TWIN FALLS CANAL COMPANY 2002 example Twin Falls reservoir accounts did not fill in 2002; Storage allocation: 210,000 acre-feet TFCC net account total space: 240,000 acre-feet A demand shortfall is also projected; TFCC forecasted supply for 2002: 992,000 acre-feet Reasonable in-season demand: 1,037,000 acre-feet demand shortfall = 1,037,000 – 992,000 acre-feet = 45,000 acre-feet

Total reasonable carryover deficit amount of 8,000 acre- feet due to Twin Falls by two weeks after day of allocation. Day of allocation in 2002 was approx. June 15

Questions/Discussion