CAPTURING ADDITIONAL WATER IN THE TUCSON AREA By The Rillito Creek Hydrologic Research Committee of The University of Arizona and The U. S. Geological Survey June 1959 Open-file Report CONTENTS Page Abstract.............................................................. 1 Introduction.......................................................... 3 Metropolitan development......................................... 3 Physical characteristics of Tucson basin......................... 4 Surficial water supplies.............................................. 8 Precipitation.................................................... 8 Runoff........................................................... 12 Sediment content of floodwaters.................................. 21 Quality of floodwaters........................................... 23 Soils............................................................ 23 Evaporation...................................................... 24 Vegetation....................................................... 28 Planned control of vegetation.......................... 31 Areas of phreatophytes................................. 31 Natural recharge of ground water................................. 31 Subsurface water supplies............................................. 34 Geology.......................................................... 34 Rock units.................................................. 34 Crystalline complex.................................... 34 Pantano beds........................................... 34 Alluvial deposits of the Tucson basin.................. 35 Alluvial fans.......................................... 37 Inner-valley fill...................................... 37 Structure................................................... 37 Physiography..................................................... 38 Ground water..................................................... 39 Occurrence and movement................................ 39 Quality of water....................................... 43 Storage and yield...................................... 46 Volumetric analyses.................................... 48 Subsurface storage of water by artificial means.................. 50 Quality of water............................................ 51 Physical properties.................................... 51 Chemical properties.................................... 51 Microbial activity..................................... 52 Location of storage areas................................... 53 Subsurface distribution and ultimate recovery of water in storage........................................... 54 Summary.............................................................. a 55 Investigations essential to the capture of additional water in the Tucson area..................................................... 55 Committee............................................................. 56 References cited...................................................... 58 ii ILLUSTRATIONS Page Figure 1. Flood on Rillito Creek, August 3, 1955..................... 6 2. Block diagram of the Tucson basin area................. in pocket 3. Geologic map of the Tucson basin area.................. in pocket 4. Mean monthly precipitation in the Tucson area and at Mount Lemmon.......................................... 9 5. Rain gages in the Tucson basin............................. 11 6. Streamflow depletion between Sabino Creek and Rillito Creek at Oracle Road bridge...................... 18 7. Surface inflow and outflow of Rillito Creek drainage....... 20 8. Annual floods of Rillito Creek near Tucson................. 22 9. Sediment rating curve, San Pedro River at Charleston....... 25 10. Index map of soil surveys, Tucson basin.................... 26 11. Relation of evaporation to temperature, Tucson, 1928-58.................................................. 29 12. Precipitation and potential evapotranspiration at Tucson and Mount Lemmon.................................. 30 13. Areas of phreatophytes with shallow water table along Rillito Creek............................................ 32 14. Conglomerate in Pantano beds............................... 36 15. Ground-water contour map of Tucson basin, spring * of 1959.................................................. 40 16. Hydrograph of water levels in two representative wells 1916-59............................................ 44 17. Quality of ground waters Rillito Creek project area....... 47 18. Ground-water lowering in Tucson basin 1947-59.............. 49 iii TABLES Page Table 1. Cooperative observers, U. S. Weather Bureau........... 12 2. Monthly and annual discharge, in acre-feet, of Rillito Creek near Tucson........................... 14 3. Summary of streamflow records available in Rillito Creek drainage.............................. 16 4. Tributaries and their estimated inflow into Rillito Creek drainage...................................... 19 5. Vegetation in the lower Rillito drainage area......... 28 6. Chemical analyses of ground water in the Tucson basin area.......................................... 43 iv CAPTURING ADDITIONAL WATER IN THE TUCSON AREA By The Rillito Creek Hydrologic Research Committee of the University of Arizona and U. S. Geological Survey ABSTRACT This report represents a pre­ crystalline complex is one of the liminary study on the possibilities principal problems requiring inves­ of increasing available water sup­ tigation . plies within the Tucson basin to meet the anticipated water demand Until disturbed by man, the a- resulting from the rapid increase in mount of water in storage in the population. The study was made by sediments of the Tucson basin re­ the University of Arizona and the mained almost constant. In recent U. S. Geological Survey. years, however, water has been with­ drawn from the basin much faster The Tucson basin is a depressed than it has been replenished by structural block between the sur­ rainfall and runoff; consequently, rounding mountain masses. The im­ static water levels have declined as permeable Pantano beds and the crys­ much as 35 feet, and net ground- talline complex compose the mountain water storage loss has been estimat­ masses and form the margin and floor ed as 250,000 acre-feet during the of the ground-water basin. The sedi­ past 12 years. It is apparent that ments which constitute the actual ground-water supplies will become ground-water reservoir are of three depleted unless measures are taken principal types: (l) alluvial depos­ to replenish the amount in storage. its of the Tucson basin,which under­ lie most of the broad,virtually flat The runoff potential in Rillito floor of the valley; (2) the inner- Creek is equal to 80 percent of the valley fill, which underlies the amount of water used in the greater flood plains of the major washes; Tucson area. Much of this incoming and (3) the alluvial-fan deposits water is lost before it can be used, along the mountain fronts. The as the potential evaporation is thickness and general configuration about nine times the annual precipi­ of the inner-valley fill and the fan tation, and vegetation along the deposits are fairly well known; how­ stream channels uses an estimated ever, the thickness of the deposits 2,500 acre-feet per year. Moreover, of the Tucson basin, the main source runoff leaving the Rillito Creek of ground water, is not certain, and basin averages about 12,000 acre- their relationship to the adjacent feet per year. and underlying Pantano beds and It is believed that additional of salient features of the Tucson water, which is now lost by evapora­ basin indicates the need for further tion or outflow from the basin via studies along several lines the Rillito Creek during the rainy sea­ pattern of precipitation throughout son, could be captured. Salvage of the basin, amounts and distribution this water would ease the pressure of runoff, quality of both surface on the ground-water reserves,through and ground water, amount of water transfer into the distribution sys­ lost by evaporation and transpira­ tem and recharge into the subsur­ tion, amount of ground water in stor­ face, where the ground-water reser­ age and its movement within the ba­ voir has been partially depleted. sin, and the feasibility of artifi­ cial recharge of the ground-water A review of present knowledge reservoir. INTRODUCTION The problem of the availability water or soil surfaces or from foli­ of water to meet the future demand age of vegetation. Virtually all of the greater Tucson area motivated water that falls as precipitation the University of Arizona and the eventually returns to the atmosphere U. S. Geological Survey to initiate as vapor. preliminary studies on the possibil­ ities of increasing available water From this continuous circula­ supplies. The basic purpose of this tion in the hydrologic system, man report is to determine the feasibil­ obtains water for his needs in agri­ ity of detailed investigations of culture, industry, and domestic use. methods for capturing additional wa­ On a continuing basis, water cannot ter in the Tucson area to supplement be withdrawn from this hydrologic municipal supplies. As metropolitan system at a rate that exceeds 're­ Tucson is the fastest growing commu­ plenishment from rainfall and run­ nity in the Southwest, owing to its off. Withdrawals at greater rates climatic appeal and commodious liv­ can be made only at the expense of ing, the population in the next 10 depleting the amount in ground-water or 15 years may be expected to in­ or soil-water