Watershed Snake River

the snake river flows through arid gorge nearing mouth in washington

the snake river thirteenth longest river in united states. watershed 10th largest among north american rivers, , covers 108,000 square miles (280,000 km) in portions of 6 u.s. states: wyoming, idaho, nevada, utah, oregon, , washington, largest portion in idaho. of snake river watershed lies between rocky mountains on east , columbia plateau on northwest. largest tributary of columbia river, snake river watershed makes 41% of entire columbia river basin. average discharge @ mouth constitutes 31% of columbia s flow @ point. above confluence, snake longer columbia—1,078 miles (1,735 km) compared 928 miles (1,493 km)—and drainage basin larger—4% bigger upstream columbia river watershed.

the semi-arid, desert climate of snake river watershed on average, receives less 12 inches (300 mm) of precipitation per year. however, precipitation in snake river watershed varies widely. @ twin falls, in center of snake river plain, climate desert, annual rainfall of 9.24 inches (235 mm), although average snowfall 13.1 inches (330 mm). desert climate occupies majority of basin of snake river, although longer columbia river above tri-cities, discharge on average less. however, in high rockies of wyoming, in upper jackson hole area, average precipitation on 30 inches (760 mm), , snowfall averages 252 inches (6,400 mm). of snake river basin consists of wide, arid plains , rolling hills, bordered high mountains. in upper parts of watershed, however, river flows through area distinct alpine climate. there stretches river , tributaries have incised tight gorges. snake river watershed includes parts of yellowstone national park, grand teton national park, hells canyon national recreation area, , many other national , state parks.

map of columbia river basin snake river highlighted in yellow , columbia river in blue

much of area along river, within few miles of banks, irrigated farmland, in middle , lower course. irrigation dams include american falls dam, minidoka dam, , c.j. strike dam. aside water river, water pulled snake river aquifer irrigation. major cities along river include jackson in wyoming, twin falls, idaho falls, boise, , lewiston in idaho, , tri-cities in washington (kennewick, pasco , richland). there fifteen dams in total along snake river, aside irrigation, produce electricity, maintain navigation channel along part of river s route, , provide flood control. however, fish passage limited stretch below hells canyon.

the snake river watershed bounded several other major north american watersheds, drain both atlantic or pacific, or endorheic basins. on southwest side divide separates snake watershed oregon s harney basin, endorheic. on south, snake watershed borders of humboldt river in nevada, , watershed of great salt lake (the bear, jordan , weber rivers) on south. snake river shares boundary green river southeast; green river drains parts of wyoming , utah , largest tributary of colorado river. on western extremity short stretch continental divide separates snake watershed bighorn river, tributary of yellowstone river, snake begins near. on north snake river watershed bounded red rock river, tributary of beaverhead river, flows jefferson river , missouri river, part of gulf of mexico drainage basin.

the rest of snake river watershed borders on several other major columbia river tributaries - spokane river north, clark fork in montana northeast , john day river west. of these, clark fork (via pend oreille river) , spokane join columbia above snake, while john day joins downstream of snake, in columbia river gorge. of note northeastern divide of snake river watershed forms idaho-montana boundary, snake river watershed not extend montana.

mountain ranges in snake watershed include teton range, bitterroot range, clearwater mountains, 7 devils mountains, , extreme northwestern end of wind river range. grand teton highest point in snake river watershed, reaching 13,775 feet (4,199 m) in elevation. elevation of snake river 358 feet (109 m) when joins columbia river.

pollution

agricultural runoff farms , ranches in snake river plain , many other areas has severely damaged ecology of river throughout 20th century. after first irrigation dams on river began operation in first decade of 20th century, of arable land in strip few miles wide along snake river cultivated or turned pasture, , agricultural return flows began pollute snake. runoff several feedlots dumped river until laws made practice illegal. fertilizer, manure , other chemicals , pollutants washed river increase nutrient load, of phosphorus, fecal coliforms , nitrogen. during low water, algae blooms occur throughout calm stretches of river, depleting oxygen supply.

dams milner dam divert water snake river irrigation, causes many of pollution problems in snake

much of return flows not issue directly snake river, rather feed snake river aquifer underneath snake river plain. water diverted river irrigation, after absorbing surface pollutants, re-enters ground , feeds aquifer. although aquifer has maintained level, has become increasingly laced contaminants. water in aquifer travels west side of snake river plain , re-enters river springs. throughout of snake river plain , hells canyon, excessive sediment recurring problem. in december 2007, u.s. environmental protection agency (epa) issued permit requiring owners of fish farms along snake river reduce phosphorus discharge 40%. pollutant levels in hells canyon upstream of salmon river confluence, including of water temperature, dissolved nutrients, , sediment, required meet levels.

discharge

the snake river s average flow 54,830 cubic feet per second (1,553 m/s). united states geological survey recorded river s discharge period of 1963–2000 @ stream gauge below ice harbor dam. in period, largest average annual flow recorded 84,190 cu ft/s (2,384 m/s) in 1997, , lowest 27,100 cu ft/s (770 m/s) in 1992. lowest recorded daily mean flow 2,700 cu ft/s (76 m/s) on february 4, 1979. on august 27, 1965, there temporarily no flow result of testing @ ice harbor dam. highest recorded flow 312,000 cu ft/s (8,800 m/s) on june 19, 1974. highest flow ever recorded on snake river @ different usgs stream gauge near clarkston, operated 1915 1972. gauge recorded maximum flow of 369,000 cu ft/s (10,400 m/s)—more columbia s average discharge—on may 29, 1948. larger peak discharge, estimated @ 409,000 cu ft/s (11,600 m/s), occurred during flood of june 1894.

the river s flow measured @ several other points in course. above jackson lake, wyoming, discharge 885 cu ft/s (25.1 m/s) drainage area of 486 square miles (1,260 km). @ minidoka, idaho, halfway through snake river plain, river s discharge rises 7,841 cu ft/s (222.0 m/s). however, @ buhl, idaho, 50 miles (80 km) downstream, river s flow decreases 4,908 cu ft/s (139.0 m/s) because of agricultural diversions , seepage. @ border of idaho , oregon, near weiser @ beginning of hells canyon, snake s flow rises 17,780 cu ft/s (503 m/s) after receiving several major tributaries such payette, owyhee , malheur. discharge further increases 19,530 cu ft/s (553 m/s) @ hells canyon dam on border of idaho , oregon. @ anatone, washington, downstream of confluence salmon, 1 of snake s largest tributaries, mean discharge 34,560 cu ft/s (979 m/s).