WSP10396 - Laserfiche WebLink

Home Browse Search

B52 DROUGHT IN THE SOUTHWEST,. 1942-56 water on the basis of established hydrologic relations at the time of the cOl,l1pact. Thus the Rio Grande Oompact of 1938 provides for the apportionment of water among the three major 'divisions of the Upper Rio Grande Basin: the San Luis Valley in Oolorado, the Middle Valley in New Mexico, and the lands served by Elephant Butte Reservoir in New Mexico and 'Texas (and Mexieo, as specified in the Treaty of 1906), The obligation of each division with respect to the next downstream divi- sion is specified iI). tabulations of relationships for vari- ous rates of strea1llflow which were developed from rec- ords covering a Ptriod of several years, Thus, although the compact makes no guarantee as to the quantity of water that shall .be available to downstream users, it attempts to insure that the stream depletions in an up- stream division shall not exceed those of the period when the specified relationships were observed, During the 1943-56 drought both of the upstream divisions failed to deliver water in accordance with compact obligations. This failure is at~ributed, in part, to increased pumping from wells and, iI). part, to losses by evapotranspiration of an increasing proportion of the available supply dur- ing the drought years (Thomas and others, 1962). The Pecos River Oompact of 1948 attempts to re- strict upstream developments by specifying that the flow of the river shall not be depleted "by man's activ- ities" below an amount which will give downstream users (in Texas) a quantit.y of water equivalent to that available under '!the 1947 condition," Thus, although the Pecos River Compact lacks schedules of inflow-out- flow relationships, it is similar (0 the Rio Grande Oom- pact in it.s object.ive of prot.ecting downstream users by limiting upst.ream deplet.ions ; and t.he history since 1947 indicat.es similar difficulty in meeting the terms of the compact, With the marked deficiencies in precipitation and resulting reduction in streamflow, it. is difficult to assess t.he stream depletions in New Mexico in relation t.o the "1947 condition," and once the change is com- put.ed there remains t.he more difficult problem of assess- ing t.he proportion of the deplet.ion that is due to man's activity, Studies prior to the compact negotiations in- dicat.ed that. the principal causes of any increase in stream deplet.ion after 1947 would be increased con- sumption of wat.er by saltcedar and t.he delayed effects of pumping from wells in t.he Roswell Basin; to these may be added t.he effects of pumping from wells drilled since 1947, nota~ly in t.he Carlsbad area (Thomas and ot.hers, 1962), The effects of' drought upon negotiat.ed apportion- ment of water and the problems raised thereby are sum- marized as follows: Apportionment of fixed quantities based on 'average streamflow falters during drought un- less the storage facilities are adequate to stabilize the natural fluctuations in runoff; and although this is rec- ognized in the Oolorado River basin and answered by plans for st.orage tot.aling more than five times the aver- age flow of the river, it is doubtful t.hat a constant yield corresponding t.o the water already apportioned can be realized throughout. the long cyclic climatic fluctuations. Apportionment on the basis of observed inflow-outflow relationships as exemplified in the Rio Grande basin provides flexibility t.o match the climatic fluct.uat.ions, and if the apportionment is equitable each user shares in the."ups and downs" of wat.er supply that. cannot. be overcome by regulat.ion, Here it would be necessary to know the hydrology in exhaustive deta,il in order to dis- criminate the natural from the artificial effects upon in- flow and outflow. The effect.s of the recent drought also serve to point up the situation in some interstate areas where no com- pacts have been negotiated for apportionment of t.he wa- ter and where in the absence of overall jurisdiction by eit.her'State t.he upst.ream user of water can enjoy the full advantage of his posit.ion, As an example, the headwaters of the Gila River have produced far less than normal st.reamflow during the drought, but pllJ't of the deficiency has probably been caused by increased pumping from wells (Thomas and ot.hers, 1963c). If the Gila basin were entirely in New Mexico, this new ground-water development. could have been st.opped by declaring the area; if the entire basin were in Arizona, howe']er, it would be difficult to prove that the wells are not. pumping "percolating" water and, therefore, diffi- cult. to deny water to a landowner, Should New Mex- ico, for the benefit. of water users in Arizona, deny wa- t.er to its own citizens when the water would not be denied to them under the laws of Arizona I It is not.e- wort.hy that the Pecos River Oompact. gives an affirma- tive answer to t.his question in a very similar situation between New Mexico and Texas: in order to deliver water't.o Texas in accordance with the Compact, it is necessary t.o restrict ground-water development and use in the Roswell basin and Carlsbad area (Thomas 'and others, 1962) ; no such restriction would be possible if the Roswell and Oarlsbad areas were in Texas, REFERENCES CITED Begemflun, Friedricb, and Libby, W. F., 1957, Continental water baiance, ground water inventory Rnd storage times, surface oc~an mixing rates, worldwide water circulation patterns from cosmic-ray and bomb tritium: Geochim. et Cosmochim. Acta, v.12. p, 277-296, Bonnen, C. A" and Ward, J. M., 1956, Some economic effects of drouth on ranch resources: Texas Agr. Expt. Sta. Bull. 801, 11 p. Buswell, A. M., and Rodebush, W. H., 1956, Water: Set. Ameri- can, v.l94, no. 4, p. 77-89.