In suomatlon, the Columbia River 

 system sbould experience no appreciable 

 dissolved oxygen reductions, other than 

 localized affects, to the year 2000 pro- 

 vided that these broad assumptions prove 

 to be valid. 



PREDICTION OF FUTUBE 

 WATER QUALITY 



The quality of water in a river 

 unaffected by man's activities is related 

 to the size of the watershed, the amount 

 of river discharge, cllmatologlcal condi- 

 tions and the nature of the soil and rock 

 fomatlons. The larger the watershed for 

 a given rate of flow, the greater will be 

 the amount of mineral matter taken Into 

 solution. Conversely, the greater the rata 

 of flow for a given watershed area, the 

 less will be the amount of matter taken 

 into solution. The solvent effect of the 

 water is dependent upon the water tempera- 

 ture, water pH or carbon dioxide content 

 and on the solubility of the soil and rock 

 fozmation in the watershed. Dissolved 

 material is usually greatest in a water 

 draining an area of fine textured, alka- 

 line soil. Noimally, the dissolved con- 

 stituents in a given stream are present in 

 an Inverse ratio to stream discharge. 

 Color and turbidity are visually present in 

 somewhat of a direct ratio to stream dis- 

 charge, increasing particularly after a 

 heavy ralnstoim. 



Man has altered this natural water 

 qioallty by the construction of reservoirs, 

 return of spent irrigation waters, dis- 

 charge of dcmestic sewage and by the dis- 

 charge of industrial wastes. In a given 

 watershed, a very detailed analysis and 

 study would be necessary to separate the 

 effect each of these man-made changes has 

 had on the river water quality constituents. 

 In general, reservoirs have their principal 

 effect on water quality by reducing turbidi- 

 ty and by changing the downstream water 

 temperatures. They may slightly increase 

 or decrease the dissolved constituents but 

 do not produce any marked effect therein 

 except, if the reservoir is large, to even 

 out the noimal changes in constituents 

 with changes in stream discharge. 



Since the marked changes in water 

 quality are then caused by Irrigation and 

 pollutants, a prediction of future water 



quality will necessitate the relating of 

 these factors to stream flow and watershed 

 area for a given drainage basin. Industrial 

 weiste discharges have been previously com- 

 puted (tables 32 €ind 3k) on a popvilation 

 equivalent basis deteimined by their bio- 

 chemical oxygen demands related to that of 

 domestic sewage. This equivalent does not 

 necessarily hold for the other constituents 

 in a waste discharge, such as dissolved 

 solids, but they are comparable and will be 

 so used for lack of a better unit or units 

 of evaluation. 



Watershed Usage Factors ; 



To combine these stream water quality 

 variables, a factor has been devised which 

 will be called the "Watershed Usage Factors". 

 This factor, with components therein in 

 units X 10^, is equal to: (Population is 

 for watershed plus Industrial waste equiva- 

 lent) 



Population X Irrigated Acreage 



Discheirge in C.F.S. X Watershead Area in Sq. Mi. 



Table 35 represents a computation of 

 these "Watershed Usage Factors" for streams 

 in the Colimibia River Basin where water 

 quality data are available for purposes of 

 future quality prediction. In the table, 

 these factors are ccanputed for the period 

 of 1910-12, 1950-56 and for the future year 

 2000. The factors for 2000 were computed 

 using the mean stream discharge of record, 

 a uniform watershed population increase 

 throughout the Columbia River Basin, as 

 shown in figure 62, and an Industrial waste 

 contribution double that of 1950. Indus- 

 trial wastes sbould more than triple In the 

 next Uo years. However, more suid improved 

 methods of industrial waste treatment should 

 be in use, thus lessening the quantity of 

 pollutants. In watersheds like the Wenatchee 

 and Deschutes where there now are no signi- 

 ficant industrial pollutants, it was assumed 

 that these woxild be built in the future to 

 the extent of their discharging pollutants 

 equivalent to the predicted population. 



The "Watershed Usage Factors" in 

 table 35 show very definitely the relation- 

 ship between the stream flow and the use 

 made of the water. The highly developed 

 Yakima River in 1950 has a visage factor 7 

 times as great as the next highest, the 

 Snake. At The Dalles the Columbia River, 

 eJ-though receiving the pollutants from the 



97 



