Civil Engineering ETDs

Publication Date

9-17-1968

Abstract

Each year a large portion of the southwestern water supply is lost through evaporation and plant transpiration. The growing water shortage in the Southwest makes vegetation manipulation and evaporation suppression to reduce these losses increasingly attractive. These losses can be successfully reduced, but it has been difficult to estimate how much additional water large scale vegetation management and evaporation control could produce. Three hydrologic models were developed for the Pecos River Basin in New Mexico to estimate the additional water which could be obtained by vegetation treatment in the forested headwater areas, the removal of salt cedar in the lower river valley, and the application of monolayer film to the major reservoirs in the Pecos Valley. The models were based on the hypothesis that the results of treatment experiments could be transposed to the Pecos River Basin by relating the additional water gained to physical and climatological parameters which were measurable both at the experimental site and in the Pecos watershed. The headwater model consisted of a precipitation-runoff relationship which generated monthly runoff from monthly precipitation and losses. The losses were supplied by a loss equation developed using data from the Wagon Wheel Gap vegetation manipulation experiment and adapted to the Pecos watershed by correlating the losses from Wagon Wheel Gap with those from the Pecos watershed. The loss equation related a loss parameter to mean monthly temperature, the departure of the monthly precipitation from normal, and a vegetation parameter. The predicted increase in water yield from the Pecos headwater regions was computed by varying the vegetation parameter to simulated timber removal. An equation relating a parameter representing salt cedar transpiration per unit of volume density to a temperature parameter and to evaporation was developed. The water consumed by salt cedar in the Pecos Valley was computed by substituting into the equation evaporation and temperature values representative of the Pecos Valley; and the net increase in water attributable to the removal of salt cedar was obtained by deducting from the water consumed the quantity of water which would be lost to increased soil evaporation, transpiration of replacement vegetation, etc. The evaporation suppression model related suppression efficiency to average wind speed and reservoir area. The amount of water which could be saved using monolayer films in the Pecos Valley was estimated from the model using average wind speeds in the Pecos Valley and the areas of the major reservoirs in the Pecos Valley. The estimated water gains from the three models were subjected to a benefit-cost analysis which showed:

1. The removal of timber from the forested headwater region of the Pecos watershed would increase the water yield by about fifteen per cent, but would not be feasible because the recreational value of the forests would far exceed the value of the additional water.

2. The annual water gain of eighty thousand acre feet from the eradication of salt cedar in the Pecos Valley would justify the cost of the salt cedar removal.

3. Suppression of evaporation during late summer and fall would be feasible in the Pecos Valley, and would save some five thousand acre feet of water annually.

Document Type

Dissertation

Language

English

Degree Name

Civil Engineering

Level of Degree

Doctoral

Department Name

Civil Engineering

First Committee Member (Chair)

John Bryan Carney Jr.

Second Committee Member

Jose Eleazar Martinez

Third Committee Member

Calvin Clyde Patterson

Fourth Committee Member

Ralph Clair d'Arge

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