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. 594 UNIVERSITY OF COLORADO LAW REVIEW l~ol. 59 60,000 S(),OOO ~ E 40 ~~ C 5 .< E ~ . - .M Ii 30 0._ . = 0:0' / 20,000 ..-- -~ _.~--.-",...,.. ---_.~--... ~ ~ ~ o ~ ~ ~ ~ :': Year ..,,0_... Total Replacement Water ~ Well Capacity Direct flow and Reservoir Storage -. Recharge Accretions = ~ FIGURE 3. GASP REPLACEMENT WATER AVAILABLE TOTAL BY SOURCE SOUrce: Jack Odor Engineering Service 2/25/87 . t988] COLORADO LAW OF "UNDERGROUND WATER" .5 at several other key locations where such a physical solution appeared possible, ., Reservoir storage and direct flow rights comprise the other major source ofreplacement water provided by GASP. Most of this water is leased on an annual basis, but GASP does own some reservoir shares as well as surface rights..' Reservoir rights provide a highly flexible supply of replacement water and generally are quite reliable, How- ever, the limited storage space along the South Platte between Hender. son and Julesburg makes it difficult to have the replacement water near the point of injury..' The final source of replacement water relied on by GASP is ob- tained through recharge projects. Recharge projects generally involve the diversion of water into a specially prepared area with high infiltra- tion rates so that the maximum possible amount of water is stored in the underlying aquifer. GASP does not operate its own recharge projects. Instead, it purchases excess credits for accretions supplied to the river by the recharge projectS of others,64 This method of augmen- tation is especially attractive because it usually involves taking water that would not otherwise be diverted (for example, during periods of low demand and high ~upply) and storing it underground so that it is available at times of need, Information provided by GASP indicates that it replaced (or had the capacity to replace) about 20 percent of the total quantity of well water pumped by its members in 1985, compared to about 13.5 per- cent in 198 L.' This change is due both to an increase in available replacement water and a decrease in the amount of groundwater pumped. 61. For an excellent discussion of thl: "physical solution" concept, see Dunning, The Physical Solution in Western Water Uzw, 57 U. CoLO. L. REV. 445 (1986). 62. GASP's 1987 plan of operation filed with the state engineer indicated total reservoir rights of about 9.000 acre-feet. roughly fourteen percent of which (about 1,250 acre-feet) was owned by GASP. Direct ftow rights (with some reservoir support) totalled about 10,800 acre-feet. twenty-four percent of which (about 2,600 acre-feet) was owned by GASP. 63. Another limitation on the use of storage water for repJacermnl is tbat the state engineer now requires that two acre-feet of such water be released for every one acre-foot of replatement credit sought. This ruling apparently is based on court decisions holding that a change in use of storage water must be limited by the historical consumptive use of the water. .see Southeastern Colo. Water Conser- vancy Dist. v. Fort Lyon Canal Company, 720 P.2d 133 (Colo. 1986). Reservoir water previously used for irrigation is assumed to have been fifty percent consumed. 64. For a description of recharge activity in the South Platte basin generafly and a discussiQIl of the projects in which GASP is involved see Warner, Sunada, & Hartwell, Recharge as Augmentation in the Sourh Platte River Basin, COLORADO WATSR RESOURCES REsEARCH INSTITUTE COMP~ETION REPORT No. 144 (Nov. 1986). 65. Jack Odor Engineering ServictS, Feb. 25. 1981. Total groundwater pumped in 1981 was about 335,000 acre-feet, while replacement water totalled about 45,500 acre-feer. In 1985 total \Vater pumped was about 275,000 acre-feet, while replacement supplies were S6,000 acre-feet.