Mapping Sources Base modified from U.S. Geological Survey 1:100,000 <strong>and</strong> 1:24,000 scale quadrangle maps. Relief from U.S. Geological Survey National Elevation Data Set 30 meter digital elevation model. <strong>Klamath</strong> Reclamation Project boundaries are from Bureau <strong>of</strong> Reclamation, <strong>Klamath</strong> <strong>Basin</strong> Area Office GIS data. Vertical datum: National Geodetic Vertical Datum <strong>of</strong> 1929 (NGVD29) Projection: Universal Transverse Mercator, Zone 10, 1927 North American Datum <strong>Ground</strong>-<strong>Water</strong> <strong>Hydrology</strong> <strong>of</strong> <strong>the</strong> <strong>Upper</strong> <strong>Klamath</strong> <strong>Basin</strong>, <strong>Oregon</strong> <strong>and</strong> California
<strong>Ground</strong>-<strong>Water</strong> <strong>Hydrology</strong> <strong>of</strong> <strong>the</strong> <strong>Upper</strong> <strong>Klamath</strong> <strong>Basin</strong>, <strong>Oregon</strong> <strong>and</strong> California By Marshall W. Gannett, Kenneth E. Lite Jr., Jonathan L. La Marche, Bruce J. Fisher, <strong>and</strong> Danial J. Polette Abstract The upper <strong>Klamath</strong> <strong>Basin</strong> spans <strong>the</strong> California-<strong>Oregon</strong> border from <strong>the</strong> flank <strong>of</strong> <strong>the</strong> Cascade Range eastward to <strong>the</strong> <strong>Basin</strong> <strong>and</strong> Range Province, <strong>and</strong> encompasses <strong>the</strong> <strong>Klamath</strong> River drainage basin above Iron Gate Dam. Most <strong>of</strong> <strong>the</strong> basin is semiarid, but <strong>the</strong> Cascade Range <strong>and</strong> upl<strong>and</strong>s in <strong>the</strong> interior <strong>and</strong> eastern parts <strong>of</strong> <strong>the</strong> basin receive on average more than 30 inches <strong>of</strong> precipitation per year. The basin has several perennial streams with mean annual discharges <strong>of</strong> hundreds <strong>of</strong> cubic feet per second, <strong>and</strong> <strong>the</strong> <strong>Klamath</strong> River at Iron Gate Dam, which represents drainage from <strong>the</strong> entire upper basin, has a mean annual discharge <strong>of</strong> about 2,100 cubic feet per second. The basin once contained three large lakes: <strong>Upper</strong> <strong>and</strong> Lower <strong>Klamath</strong> Lakes <strong>and</strong> Tule Lake, each <strong>of</strong> which covered areas <strong>of</strong> 100 to 150 square miles, including extensive marginal wetl<strong>and</strong>s. Lower <strong>Klamath</strong> Lake <strong>and</strong> Tule Lake have been mostly drained, <strong>and</strong> <strong>the</strong> former lake beds are now cultivated. <strong>Upper</strong> <strong>Klamath</strong> Lake remains, <strong>and</strong> is an important source <strong>of</strong> irrigation water. Much <strong>of</strong> <strong>the</strong> wetl<strong>and</strong> surrounding <strong>Upper</strong> <strong>Klamath</strong> Lake has been diked <strong>and</strong> drained, although efforts are underway to restore large areas. <strong>Upper</strong> <strong>Klamath</strong> Lake <strong>and</strong> <strong>the</strong> remaining parts <strong>of</strong> Lower <strong>Klamath</strong> <strong>and</strong> Tule Lakes provide important wildlife habitat, <strong>and</strong> parts <strong>of</strong> each are included in <strong>the</strong> <strong>Klamath</strong> <strong>Basin</strong> National Wildlife Refuges Complex. The upper <strong>Klamath</strong> <strong>Basin</strong> has a substantial regional ground-water flow system. The late Tertiary to Quaternary volcanic rocks that underlie <strong>the</strong> region are generally permeable, with transmissivity estimates ranging from 1,000 to 100,000 feet squared per day, <strong>and</strong> compose a system <strong>of</strong> variously interconnected aquifers. Interbedded with <strong>the</strong> volcanic rocks are late Tertiary sedimentary rocks composed primarily <strong>of</strong> fine-grained lake sediments <strong>and</strong> basin-filling deposits. These sedimentary deposits have generally low permeability, are not good aquifers, <strong>and</strong> probably restrict ground-water movement in some areas. The regional groundwater system is underlain <strong>and</strong> bounded on <strong>the</strong> east <strong>and</strong> west by older Tertiary volcanic <strong>and</strong> sedimentary rocks that have generally low permeability. Eight regional-scale hydrogeologic units are defined in <strong>the</strong> upper <strong>Klamath</strong> <strong>Basin</strong> on <strong>the</strong> basis <strong>of</strong> surficial geology <strong>and</strong> subsurface data. <strong>Ground</strong> water flows from recharge areas in <strong>the</strong> Cascade Range <strong>and</strong> upl<strong>and</strong> areas in <strong>the</strong> basin interior <strong>and</strong> eastern margins toward stream valleys <strong>and</strong> interior subbasins. <strong>Ground</strong> water discharges to streams throughout <strong>the</strong> basin, <strong>and</strong> most streams have some component <strong>of</strong> ground water (baseflow). Some streams, however, are predominantly ground-water fed <strong>and</strong> have relatively constant flows throughout <strong>the</strong> year. Large amounts <strong>of</strong> ground water discharge in <strong>the</strong> Wood River subbasin, <strong>the</strong> lower Williamson River area, <strong>and</strong> along <strong>the</strong> margin <strong>of</strong> <strong>the</strong> Cascade Range. Much <strong>of</strong> <strong>the</strong> inflow to <strong>Upper</strong> <strong>Klamath</strong> Lake can be attributed to ground-water discharge to streams <strong>and</strong> major spring complexes within a dozen or so miles from <strong>the</strong> lake. This large component <strong>of</strong> ground water buffers <strong>the</strong> lake somewhat from climate cycles. There are also ground-water discharge areas in <strong>the</strong> eastern parts <strong>of</strong> <strong>the</strong> basin, for example in <strong>the</strong> upper Williamson <strong>and</strong> Sprague River subbasins <strong>and</strong> in <strong>the</strong> Lost River subbasin at Bonanza Springs. Irrigated agriculture is an integral part <strong>of</strong> <strong>the</strong> economy <strong>of</strong> <strong>the</strong> upper <strong>Klamath</strong> <strong>Basin</strong>. Although estimates vary somewhat, roughly 500,000 acres are irrigated in <strong>the</strong> upper <strong>Klamath</strong> <strong>Basin</strong>, about 190,000 acres <strong>of</strong> which are part <strong>of</strong> <strong>the</strong> Bureau <strong>of</strong> Reclamation <strong>Klamath</strong> Project. Most <strong>of</strong> this l<strong>and</strong> is irrigated with surface water. <strong>Ground</strong> water has been used for many decades to irrigate areas where surface water is not available, for example outside <strong>of</strong> irrigation districts <strong>and</strong> stream valleys. <strong>Ground</strong> water has also been used as a supplemental source <strong>of</strong> water in areas where surface water supplies are limited <strong>and</strong> during droughts. <strong>Ground</strong> water use for irrigation has increased in recent years due to drought <strong>and</strong> shifts in surfacewater allocation from irrigation to instream uses. The shifts in surface-water allocation have resulted from efforts to improve habitat for fish listed under <strong>the</strong> Federal Endangered Species Act. The ground-water system in <strong>the</strong> upper <strong>Klamath</strong> <strong>Basin</strong> responds to external stresses such as climate cycles, pumping, lake stage variations, <strong>and</strong> canal operation. This response is manifest as fluctuations in hydraulic head (as represented by fluctuations in <strong>the</strong> water-table surface) <strong>and</strong> variations in ground-water discharge to springs. <strong>Basin</strong>wide, decadal-scale climate cycles are <strong>the</strong> largest factor controlling head <strong>and</strong> discharge fluctuations. Climate-driven water-table fluctuations <strong>of</strong> more than 12 feet have been observed near <strong>the</strong> Cascade
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