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Irrigated Lands and Zone Matching <br />The GIS coverage of irrigated parcels was combined with a GIS coverage of the URF zones to <br />create a space delimited ASCII database file containing the irrigated parcel to URF zones <br />relationships, rg.p2z. URF zones are shown in Figure 1. Every irrigated parcel that is located <br />within the URF zones is in this file. For more detailed information about this file, see <br />Attachment 1. <br />River Reach and Model Node Matching <br />Unit response functions were generated by the groundwater model for each URF zone. However, <br />only those URF's determined by HRS to have significant impacts on a river reach within the <br />basin were used to generate return flow patterns. Each selected URF relates a recharge or <br />pumping in a URF zone to a specific river reach. A space delimited ASCII database file is used <br />to define the URF zone to URF relationships, rg.z2u. Another space delimited ASCII database <br />file is used to define the URF to river reach relationships, rg. u2r. <br />Within each river reach, three to four StateMod network nodes were selected for the return flows <br />based on structure location and topography. Each node is assigned a percentage of the total <br />returns for this reach. A space delimited ASCII database file is used to define the river reach to <br />network node relationships and percentages, rg.r2n. <br />Surface /Groundwater Return Flow Split <br />The user of the makertn utility may specify defaults for the percent of return flow occurring <br />immediately (surface returns) and default patterns for those diversion structures irrigating lands <br />outside of the groundwater model domain. For the Rio Grande model, the default immediate <br />return percentage has been set to 5 percent of diverted water. An 18-month return pattern has <br />been assigned to those diversion structures where URFs are unavailable. <br />Return Flow StateMod File <br />makertn was run using the previously described database inputs. The result of this effort is the <br />return flow file, rg.rtn. Information in the return flow file is then incorporated into the direct flow <br />station file (rg.dds) when created using the DMI watright. <br />Comments and Concerns <br />Most of the return flows used in the Phase la StateMod model are based on the URF's previously <br />described. However, the irrigated areas of approximately 85 structures were not mapped by the <br />Consumptive Use Contractor within the ground water model area. Return flow patterns and <br />locations for diversion structures that were not mapped within the groundwater model domain <br />were set to a default 18-month lag pattern, with returns occurring at the next downstream <br />diversion structure using engineering judgement (e.g. many of these structures are outside the <br />ground water model area and generally located in the upper portion of water sheds that contains a <br />relatively narrow alluvium). <br />Attachments <br />1. makertn documentation <br />2. StateMod return flow file (rg. rtn) <br />C:Acdss\Task6-4.doc Return Flow Characteristics February 24, 2000 -Page 3 of 5 <br />