Table 7.10 — Expected water supplies in the 

 United States, by water resource region 



(Billion gallons a day) 



Water resource 



Cc 



nfidence level' 



region 



Mean 



80 percent 



95 percent 



New England 



78.2 



62.7 



48.3 



Middle Atlantic 



79.2 



61.2 



48.4 



South Atlantic Gulf 



228.0 



164.1 



121.8 



Great Lakes 



72.7 



57.3 



44.9 



Ohio 



178.0 



141.0 



105.0 



Tennessee 



40.8 



35.9 



31.4 



Upper Mississippi 



121.0 



91.8 



65.3 



Lower Mississippi 



433.0 



282.0 



202.0 



Souris-Red Rainy 



6.0 



3.4 



1.8 



Missouri 



44.1 



29.9 



17.6 



Arkansas-White-Red 



62.6 



37.4 



21.6 



Texas Gulf 



28.3 



12.3 



6.3 



Rio Grande 



1.2 



.3 



.2 



Upper Colorado 



10.0 



7.0 



3.9 



Lower Colorado 



1.6 



1.4 



1.2 



Great Basin 



2.6 



1.6 



1.2 



Pacific Northwest 



255.3 



213.3 



179.7 



California 



47.4 



29.8 



19.5 



Alaska 



905.0 



795.0 



705.0 



Hawaii 



6.7 



4.9 



3.8 



Caribbean 



4.9 



3.3 



1.6 



' The quantity of water supply expected annually on the average and at 80 and 95 

 percent probability level- 

 Source: See source note table 7 1 



In general, the eastern United States is expected 

 to have few water shortage problems at the subregion 

 level. The Northeast region has no subregions where 

 water quantity problems are anticipated during the 

 projected years. Nor does there appear to be major 

 seasonal problems since consumptive use does not 

 exceed 90 percent of the supply in any month (table 

 7.11). Yet, in the early 1960's, the Northeast region 

 experienced a drought that had a severe impact on 

 supplies. Such problems could be expected to occur 

 again, though infrequently (less than 10 out of 100 

 years). 



Within the North Central region, water quantity 

 problems are most likely in the Southwestern Lake 

 Michigan subregion (0403). The dry year supply will 

 be depleted by 55 percent by 1985 and by 80 percent 

 by 2000. The 95 percent supply (1 in 20 years) would 

 fall considerably below annual consumption needs. 

 A small increase in demand in combination with 

 drought conditions could amplify the problem. Manu- 

 facturing and electric cooling will be major water 

 consumers in this subregion, and would hkely be most 

 severely affected in a drought year. 



In the Southeast Region, only the Southern Florida 

 (0305) subregion in the South Atlantic Gulf is Ukely 

 to experience significant flow depletion. It is signifi- 

 cant that in 20 percent of the years, streamflow will 



be depleted in excess of 90 percent for 5 months. 

 This shows a serious seasonal supply problem, and 

 could represent a substantial problem for instream 

 values. 



Within the South Central region, several subregions 

 show potential depletion problems. The Canadian 

 (1105) and the Red-Washita (1106) subregions have 

 only moderately high depletion rates, but their water 

 supply problem is critical because of the high rates 

 of ground water mining. In the Canadian subregion 

 (1 105), ground water mining accounts for 68 percent 

 of the average year supply. The monthly analysis 

 shows a large difference in the number of months 

 that consumptive use exceeds 90 percent supply with 

 and without ground water mining. 



Also in the South Central, the Brazos (1203) and 

 the Colorado (1204) subregions show high depletion 

 ratios, especially in the dry years, though they cur- 

 rently exceed 50 percent depletion in the average 

 year. More than half of the months show an excess 

 of 90 percent depletion during the dry year in these 

 two subregions. In much of the High Plains area, 

 irrigation is heavily supported by ground water min- 

 ing, which supplies 39 percent and 24 percent of the 

 average supply in subregions 1203 and 1204, respec- 

 tively. A water shortage in the future could severely 

 affect the economy of the South Central Region, 

 which is heavily dependent on irrigated agriculture. 

 Both the Rio Grande-Pecos ( 1 303) and the Lower Rio 

 Grande (1305) are likely to experience major deple- 

 tions, the latter exceeding 90 percent in all dry years. 



The Great Plains region includes four subdrainages 

 in the Missouri River Basin and one in the Arkansas- 

 White-Red River Basin. The Niobrara-Platte-Loup 

 (1008), Kansas (1010), and the Arkansas-Cimarron 

 (1103) all show high depletions currently ranging 

 from 58 to 113 percent in the dry year. Irrigation 

 accounts for more than 90 percent of the water con- 

 sumed in these subregions; consequently, the agricul- 

 tural economy will be impacted the greatest in years 

 of short supply. Ground water overdraft is fairly 

 significant in the Kansas and Arkansas-Cimarron 

 drainages. 



The Rocky Mountain Region, which includes parts 

 of the Missouri, Rio Grande, Colorado, Great Basin, 

 and the upper drainages of the Columbia Rivers, 

 has several subregions that have potential water quan- 

 tity problems. These are discussed as part of the major 

 drainages. 



In the Missouri River portion of the Rocky Moun- 

 tain Region, the No/ So Platte (1007) will approach 

 90 percent depletion in any dry year. The No/ So 

 Platte is experiencing seasonal water shortages and is 

 mining large amounts of ground water. Irrigation, 

 which accounts for more than 90 percent of consump- 

 tion, will be impacted most during years of short 



292 



