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• Rio Grande Canal <br />• Farmers Union Canal <br />• Empire Canal <br />• San Luis Valley Canal <br />• Prairie Canal <br />• Monte Vista Canal <br />• Excelsior Canal <br />• Centennial Canal <br />The Big Eight Canal systems represent approximately 90 percent of all diversions from the Rio <br />Grande in most years. Together with the Big Eight, several other large canal systems (Costilla, <br />Lariat, Piedra, and Chicago) comprise nearly 95 percent of surface waters diverted from the Rio <br />Grande annually. <br />The larger canal systems on the Rio Grande are considered to be among the most efficient along <br />the river in terms of water control and measurement. Each of the Big Eight have been fitted with <br />satellite telemetry equipment to control and report water diversion amounts. All but the <br />Centennial and Excelsior canals also have rated sections or boxes. Many other smaller ditch <br />systems have less sophisticated measurement devices. All structures with rights in excess of 10 <br />cfs are fitted with some type of automatic recording device. Moss and weed growth within ditch <br />channels is not uncommon and can adversely affect the accuracy of measurement devices (e.g. <br />Centennial Ditch and Chicago Ditch). <br />Use of direct flow rights typically occurs during the period April 1 through October 31. <br />However, variations in climatic conditions may often result in minor extension or shortening of <br />this "irrigation season." In addition to the use of direct flow rights for meeting crop requirements <br />during the irrigation season, many ditches are involved in intentional efforts to recharge the <br />unconfined aquifer. This is accomplished through both passive efforts (ditch seepage and <br />application losses) and through active means (recharge pits). The intent of these efforts is to <br />recharge the underlying aquifer such that it can later be extracted and applied using groundwater <br />wells. The earliest ditches to have their direct flow decrees changed to recognize recharge as a <br />beneficial use include the Rio Grande Canal and Farmers Union Ditch (Case Nos. W-3979 and <br />W-3980). Additional information concerning use of direct flow water rights for the purpose of <br />recharging the unconfined aquifer can be found in memoranda documenting interviews with ditch <br />companies. <br />In Case No. 79CW091, use of direct flow irrigation rights for six ditches was decreed for the <br />months of November and December for the purpose of recharging the unconfined aquifer. The <br />decree allowing use of these rights during November and December and "winter recharge" carries <br />several terms and conditions, including Compact considerations. This decree is provided as <br />Attachment 2 to this memorandum. <br />District Commissioners are aware of several diversions structures and canal systems that have <br />physical capacities that are less than their total decreed water rights. This is due largely in part to <br />changes in irrigation practices from surge to sprinklers. For example, the Farmers Union Canal, <br />with decrees totaling approximately 800 cfs is only able to physically divert and carry about <br />three-quarters of this amount for any sustained period. Commissioners indicated that <br />examination of historical diversion records may well be the best indicator of actual capacities of <br />diversion structures on the River. <br />C:Acdss\D20_Mem.doc District 20 Interview July 2, 1999 -Page 3 of 9 <br />