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-5- (b) You assume full use in both the Upper and Lower Basin (that is, a use of a total of 16,000,000 acre-feet) and give the United States no credit for any return flows. Under the Treaty, Article ll, the United States may deliver the water allotted to Mexico ~erever these waters may arrive in the bed of the limitrophe section of the Colorado River" with the exception of deliveries made through the All-American Canal and at the Sonora boundary. Hence all return now water appearing ~n the limitrophe section of the river is a credit to the United States." It is reasonable to assume that with full use of the Lower Basin share of Colorado River water, there will be return nows which will go to make up the Mexican deliveries. At the hearings before the Senate Foreign Relations Commtttee on the Treaty, prominent engineers testi- fied that the return flows would, in their 'opinion, be adequate to supply the Mexican all~tment without a...'lY demand on water allotted to the Upper or LONer Basins. The following state- ment contained in the report of the united States Senate Foreign Relations Committee 'on the Mexican Water Treaty (Executive Report No.2, 79th Congress, 1st Session, p. 4) should be noted: . "Certain limitations are placed upon the schedules of delivery so as to insure to the United States credit for substantially all return flOV1S and other waste yraters emanating from projects within the Un,ited States and generally reaching the river at points too low on the stream to be susceptible of further use within the United States. This is largely composed of water which has been used for the irrigation of lands within the United States and which returns to the ri. ver through drainage canals or through under- ground seepage. Not all of the water wl)ich is put' upon the land is consumed in plant transpiration and seepage. The residue, which is a substantial part of the amount diverted, eventually finds its way back into the stream. This water, which will pass down the river to Mexico in any event, is supplemented b;y flood-waters and other excess waters which are used for desilting, canal sluicing, and other purposes. Engineers of the Bureau of Reclamation and the American section of the Boundary Commission estimate that, when full develop- ment has been reached in the United States, these ' return nows will be not less than 900,000 acre-feet a ear,' and perhaps as much as 1 125,000'acre-feet a ~ear, thus' limiting the raft ' what might beca~led firm ' ,/ -'.<;.,,:-ci