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f~ :'1 ;~1 located between Otowi Bddge and San Marcial with sevetal diversions and drainage retums. The sta- tion at San Marcial is at the upper end of Elephant Butte Reservoir and the station at Elephant Butte Dam is at the lower end of the Reservoir. The station below Caballo Dam is at the upper end of the inigated area of the Rio Grande PfOject. Water is diverted at Caballo Dam for the Rincon Division, at Leasburg Dam fm the Mesilla Division and at El Paso fm the El Paso Division and the Hudspeth County Distfict. The station at Fort Quitman, is at the lower end of the dver section included in this study and is appwximately 450 ,miles below Otowi Bddge at the upper end. OISSOL VEO SOLIDS The annual maximum, minimum and mean discharge figures for the seven gaging stations are shown in Table 1. The flow at Otowi Bddge vaded fwm a minimum of 380,000 acre-feet in 1934 to 2,593,000 acre-feet in 1941 with an average of 1,079,000. Be- low the Reservoir there was less year-to-year vari- ation. The maximum was reached in 1942 and the minimum in 1951 or 1952. .Table 1. Discharge far Seven Stations an the Ria Grande far the 20-year Period 1934-1953 ( Provisional Records) .:~ ~." ".;" ~1 -:1 ;j ::1 :~ " ., Stations on the ANNUAL DISCHARGE ( 1,000 ac-ft) Rio Grande Maximum Minimum Mean Otowi Bridge 2,593 380 1,079 San Marcial 2,832 114 853 Elephant Butte 1,819 429 790 Caballa Dam 1,796 469 781 Leasburg Dam 1,764 432 743 El Paso 1,559 252 525 Fort Qui tman 1,270 11 203 The total concentration in parts per million of dissolved solids and in terms of electrical conducti- vity in micromhos/cm, for each of the seven gaging stations is shown in Table2. In terms of quality fm irrigation use, the water at Otowi Bridge is of low salinity. From San Marcial to Leasburg Dam it is classed as of medium salinity; at El Paso high; and at Fort Quitman of very high salinity. Table 2. Total Concentration in Parts per Million and in Terms of Eleclfical Conductivity far Seven Stations on the Rio Grande for the 20-year Period 1934- 1953 TOTAL CONCENTRATION (Weighted Mean) Dissolved Solids Electrical Conductivity (Parts per million) (ECxlQ6 at 250 C.) Stations on the Rio Grande Otowi Bridge 221 311 San Marcial 449 677 Elephant Butte 478 726 Caballo Dam 515 779 Leasburg Darn 551 827 EI Paso 787 1,187 Fort Quitman 1,691 2,630 Fm salt-bwden or salt-balance calculations, the dissolved solids are expressed in tons per acre-foot, as shown in Table 3. Table 3. Dissolved Solids in Tons per Acre-foot for Seven Stations on the Rio Grande for the 20-year Period 1934-1953 Stations on the Rio Grande Otowi Bridge San Marcial Elephant Butte Cahallo Dam Leasburg Dam EI Paso Fort Quitman DlSSOL VED SOLIDS (tons pet ac-ft) Maximum Minimum Weighted Mean 0.40 1.10 .92 .96 .97 1.27 5.25 0.25 .46 .49 .56 .60 .79 1.20 0.30 .61 .65 .70 .75 1.07 2.30 It w ill be noted that there was much less vafiation in concentration than there was in discharge. The calculation of the annual salt burden is com~ paratively simple. The product obtained by multi- plying the discharge in acre-feet per year by the concentration in tons per acre-foot gives the tonnage of salt per year. This is summarized in Table4. Table 4. Salt Burden for Seven Stations on the Rio Grande for the 20-year Period 1934.1953 Stations on the Rio Grande Otowi Bridge San Marcial Elephant Butte Caballo Dam Leasburg Dam EI Paso Fort Quitman MEAN DISCHARGE (Thousands of acre-feet per year) 1,079 853 790 781 743 525 203 DlSSOL VEDSOLIDS (Weighted Mean) (Tons per acre-feet) 0.30 .61 .65 .70 .75 1.07 2.30 DISSOLVED SOLIDS (Thouaands of tons per yead 324 520 514 547 557 562 467 41 "\ -, r, " ("' ,~ \.: :_It:.. .., V U