SUN RIVER PROJECT Operating Guide For Greenfields Irrigation District January 2021 The Sun River Project operational guide is to document the available tools and resources to assist Greenfields Irrigation District (GID) with operational decisions at Gibson Dam and the Sun River Project. This guide is not all-inclusive and is not meant to replace any information in other official Reclamation documents. This guide is a collaborative effort by GID, Reclamation, Sun River Watershed Group, Trout Unlimited, Montana Department of Natural Resource, and the Montana Fish, Wildlife, and Parks to document operational information. Table of Contents Water Rights.......................................................................................................................... 3 Storage ................................................................................................................................ 3 Natural Flow of the Sun River .............................................................................................. 3 Broken O Ranch .................................................................................................................. 4 MT FWP Instream Reservation ............................................................................................ 4 Water Right Agreements ...................................................................................................... 4 Data Used in Operations........................................................................................................ 5 U.S. Geological Survey (USGS)........................................................................................... 5 National Weather Service (NWS/NOAA) ............................................................................. 5 Reclamation – HydroMet ..................................................................................................... 5 Table 1. Sun River Watershed Gage Information............................................................... 6 Natural Resource Conservation Service (NRCS) ................................................................... 7 Figure 1. NRCS SNOTEL Sites ........................................................................................ 7 Gibson Reservoir Inflow Forecasting Tools .......................................................................... 8 Reclamation ........................................................................................................................ 8 Figure 2. Example: PyForecast Plots................................................................................. 8 Natural Resource and Conservation Service .......................................................................... 8 Figure 3. Example: NRCS Forecast .................................................................................. 9 Sun River Watershed ........................................................................................................... 9 Figure 4. Example: Estimating Peak Inflow .................................................................... 10 Figure 5. Example: Estimating Peak Inflow Day ............................................................. 10 National Weather Service................................................................................................... 10 Figure 6. Example: NWS Forecast ................................................................................. 11 General Operations ............................................................................................................. 11 Gibson Dam – Spring Operations (March – July)............................................................... 12 Figure 7. Example: Operating Rule Curve ...................................................................... 13 Table 2. Gibson Release vs. Gibson Storage.................................................................... 13 Figure 8. Example: North & South Fork Flows vs. Temperatures..................................... 14 Gibson Dam – Summer Operations (July – September) ..................................................... 15 Figure 9. Drought Adjustment to Forecast....................................................................... 16 Figure 10. Minimum Flow at Simms Gage ...................................................................... 16 Gibson Dam – Winter Operations (October – February) ................................................... 17 Figure 11. October through March Inflow Forecast Plot .................................................. 18 Contact Information ............................................................................................................ 19 2 Water Rights Water rights for the Sun River Project are based on Montana law. Water rights in Montana are guided by the Prior Appropriation Doctrine, that is, “first in time is first in right.” The Project water rights have been adjudicated in a Temporary Preliminary Decree. These water rights reflect historical use but still need to go through a Preliminary Decree before being finalized in the Montana Water Court. The Project has water rights for storage and for natural flow. The water rights discussed below are the primary water rights that affect project operations. Storage Storage water rights are held in Reclamation’s name. The Gibson Reservoir water right has a claimed priority date of November 6, 1917 for a volume of 99,058 acre-feet. Gibson Reservoir was authorized as a single purpose, irrigation facility. Water rights were claimed for irrigation, recreation, and fish and wildlife. The water right for filling Gibson Reservoir is based on the capacity of the reservoir as it existed when the water rights were filed in 1981. Gibson Reservoir is on-stream and can legally store water year around. Therefore, water is stored under its priority date whenever it is legally available and there is room to store it up to the volume limit. Gibson Reservoir should only store water when the summation of reservoir inflows and downstream accretions exceed the needs of downstream water right with priorities earlier than November 6, 1917. Willow Creek Reservoir has water rights from two sources – Willow Creek and the Sun River. The primary use of the water is for irrigation but there are also water right claims for recreation and fish and wildlife. The Willow Creek water rights have priority dates of 1883, and 1906 for the 32,000 acre-feet capacity of Willow Creek Reservoir. Sun River water is delivered to Willow Creek Reservoir through the Willow Creek Feeder Canal with a 1905 priority date. Willow Creek Reservoir is off-stream and water is only diverted to Willow Creek Reservoir under its priority date from April to October. Pishkun Reservoir has a direct flow right also with a 1905 priority date. The reservoir is also an off-stream reservoir and is filled using this right as well as by transferring storage from Gibson Reservoir. Pishkun Reservoir water is used for irrigation by Greenfields Irrigation District (GID). Natural Flow of the Sun River Natural flow water rights are held jointly by Reclamation and the Irrigation Districts. There are seven previously decreed water rights with priority dates from 1870-1891 for 31.41 cfs that provide irrigation water for Ft. Shaw Irrigation District (FSID). There is one previously decreed right with an 1880 priority, and one filed right with a 1906 priority date that provides irrigation water to GID. Reclamation filed two additional rights on May 25, 1905, for direct flow from the Sun River. Ft. Shaw and GID share the water available from these rights through an agreement. 3 Ft. Shaw Irrigation District encompasses 27,273 acres and is allowed to irrigate 13,849 acres in an irrigation season. GID encompasses 133,831 acres and is allowed to irrigate 83,231 acres in an irrigation season. Broken O Ranch Broken O Ranch has 26 water rights on the Sun River. Thirteen of these rights are for irrigation areas that range from 12 acres to 20,000 acres. The priority dates range from 1871 to 1954. They also have 13 rights for stock use. These priority dates range from 1862 to 1910. Montana Fish, Wildlife and Parks (MT FWP) Instream Reservation MT FWP has two water rights with 1985 priority dates for instream flow on the Sun River. One right is for 100 CFS and protects a reach on the Sun River from the diversion dam below Gibson Reservoir to Elk Creek (Reach 1). The second instream right is for 130 cfs and protects a reach on the Sun River from Elk Creek to the Missouri River (Reach 2). These instream reservations are based on the lower inflection point using the wetted perimeter methodology as described in the Upper Missouri River Basin Final Order (1992). This methodology identifies a lower and upper inflection point based on the wetted distance along the bottom and sides of a channel cross-section. Below the lower inflection point, the wetted perimeter changes rapidly with changes in flow. As flows increase above the lower inflection point toward the upper inflection point, changes in wetted perimeter decline. The upper inflection point provides the minimum streamflow that will cover most of a stream’s riffle area resulting in a flow that will protect food-producing capacity (aquatic invertebrate production) and adequate spawning and rearing conditions. Most water reservations in the Upper Missouri River Basin were based on the upper inflection point; however, the lower inflection point was used for the Sun River based on the severe dewatering and the suppressed