Browsing by Author "Reddell, D. L."

Now showing 1 - 7 of 7

Comparison of Methods for Determining Soil Hydraulic Characteristics
(Texas Water Resources Institute, 1980-12) Humphreys, K. B.; Newton, R. J.; Brown, K. W.; Reddell, D. L.; McFarland, M. J.; Howell, T. A.
An adequate description of soil moisture movement is necessary for solution of agriculturally oriented problems such as irrigation, drainage and runoff control. Three approaches for determining the hydraulic properties of soil are in situ measurements, laboratory measurements and theoretical models. Field measurements, though representative, have the disadvantages of being costly and time consuming. Laboratory and mathematical processes are more practical but require extensive comparison to field results for evaluation. The purpose of this study was to determine the principle hydraulic properties of a soil of the Norwood Series utilizing the three approaches and to compare the results. The laboratory method selected was centrifugation (Alemi, et al., 1972). Soil cores were centrifuged and the redistribution of water was measured as change in weight with time. Inconsistent results and limited data obtained with this method, consequently, prevented adequate conclusions from being made. Hydraulic conductivity was obtained by measurement of hydraulic head and moisture content of the soil profile in situ with tensiometers and neutron probe, respectively. The theoretical procedure utilized water retentivity curves in conjunction with values of saturated hydraulic conductivity for computing hydraulic conductivity as a function of water content. Saturated hydraulic conductivity was measured in the field using Bouwer's (1961) double-tube method. The pressure-water content curves were obtained with disturbed soil samples for 30 to 80 cm depths and with soil cores for O to 15 cm depths using pressureplate extractors. A combination of laboratory and field measured values for these curves was also used for comparison. The field measurements yielded several relationships between hydraulic conductivity and water content, varying with soil depth. Comparison of calculated values with field data using only the laboratory water retention curves gave mediocre results for the 30 to 80 cm soil depth. However, when the field and laboratory data were combined and the resulting water retention curve was used to calculate hydraulic activity, the correlation was greatly improved. The O to 20 cm soil depth showed good results with both curves. Thus, it appears that this theoretical technique is applicable to soils of the type studied, but the accuracy of the calculated values is quite sensitive to the shape of the water retention curve, the saturated water content value and the saturated hydraulic conductivity value. Thus, accurate measurement of these parameters is necessary for its successful use.
Determining the Transpiration Rate of Peach Trees Under Two Trickle Irrigation Regimes
(Texas Water Resources Institute, 1980-12) Reeder, E. L.; Van Bavel, C. H. M.; Rodrigue, P. B.; Newton, R. J.; Brown, K. W.; Reddell, D. L.; McFarland, M. J.; Howell, T. A.
The scientific design and management of a modern irrigation system requires that the designer or manager have knowledge of site and plant criteria such as infiltration, drainage, soil fertility, plant water needs, and plant production under varying conditions. With modern trickle systems water control is very precise and thus precise information on irrigation needs of a crop allow for the optimal use of water supplies. Work has been conducted on the effects of trickle irrigation on peach trees in North Central Texas. Initial data relating trickle irrigation amounts to total production, peach size, and plant growth have indicated that trickle irrigation may provide benefits that would offset costs of the irrigation system and water. Previous work however has related these benefits only to the amount of water applied through irrigation and did not consider the total water use of the tree. Research was undertaken to determine the transpiration rate of peach trees under two trickle irrigation regimes. To determine the transpiration rate a volume of soil around the test trees was instrumented with neutron access tubes. Soil moisture depletion was measured weekly. A soil water balance was conducted equating evapotranspiration to the sum of the change in the soil moisture content (a decrease being positive) plus irrigation applied, plus any rainfall that occurred in the period. For this work runoff and flux across the measurement zone boundaries was assumed zero. Estimates of evaporation from the soil surface were made using a two-stage evaporation process along with values of potential evapotranspiration made with the Penman (1956) equation. The estimates of evaporation from the soil surface were subtracted from total evapotranspiration to give estimates of the transpiration of the peach trees. Estimates of transpiration were not consistent from one measurement period to the next. Errors in the estimation of evaporation from the soil surface directly affect the estimate of transpiration. During latter stages of a rain-free period an estimate of transpiration was made which should not have been influences by the low values of evaporation from the soil surface that existed. This method of estimating transpiration has many errors and can be much improved upon by using a method such as a lysimeter to estimate transpiration more accurately.
Heat Transport in Groundwater Systems--Finite Element Model
(Texas Water Resources Institute, 1980-08) Reddell, D. L.; Grubaugh, E. K.
Solar energy is a promising alternate energy source for space heating. A method of economic long term solar energy storage is needed. Researchers have proposed storing solar energy by injecting hot water heated using solar collectors into groundwater aquifers for long term energy storage. Analytical solutions are available that predict water temperatures as hot water is injected into a groundwater aquifer, but little field and laboratory data are available to verify these models. The objectives of this study were to construct a laboratory model to simulate hot water injection into a confined aquifer, to use data from the model to verify analytical solutions modeling this process, and to evaluate the effects of physical properties and design parameters on thermal recovery efficiency. Initial studies of hot water injection into underground reservoirs were done by the petroleum industry while studying secondary and tertiary oil recovery methods. These studies involved small laboratory models. Advances in computer technology made it possible to model these systems numerically. Many assumptions must be made to predict temperature distributions and thermal efficiencies using analytical models which are not required in numerical solutions. To simulate hot water injection into a confined aquifer, a laboratory model (a 1.8288 m deep, 0.2 radian sector tank, that was 7.01 m in the radial direction) was constructed. There were 39 temperature and 15 fluid pressure measuring locations through the model. Water was supplied to the model at a constant temperature and flow rate. The flow layer was composed of a fine grained Texblast blasting sand. Four runs were made. During the initial run, no heat transfer took place and the hydraulic conductivity was measured. Three runs were made where the heat transfer was monitored. Water level data from the heat transfer runs showed that as the temperature of the aquifer increased, the hydraulic conductivity increased. Temperature data indicated that the three radii closest to the well bore reached thermal equilibrium. The equilibrium temperature decreased as radius increased. From Run 1 to Run 2, the equilibrium temperature increased at each radius because a larger flow rate was used. A vertical thermal gradient existed in the flow layer with the less dense warm water floating out over the cooler more dense water initially in the model. During the pumping cycle, the temperatures gradually decreased. The temperature of the water as it was pumped out of the model was measured and the energy recovered was computed using the initial temperature as a reference. Various other temperatures were used as a base reference to calculate recovery efficiency. There were heat losses out the sides of the model. The assumption of angular symmetry made in all analytical solutions was therefore not met. For this reason, the analytical solutions showed adequate, but not great, agreement with the experimental temperature distributions. Using the analytical solutions, the effects of changing system design parameters were evaluated. Increasing thermal conductivity in the flow layer caused the temperature distribution to spread out but had no effect on thermal efficiency. Increasing the thermal conductivity in the confining layers caused the temperature profile to not move as far from the well, and decreased thermal efficiency. Injection rates are only indirectly related to thermal efficiency. The physical parameter having the greatest effect on thermal efficiency was the flow layer thickness. As thickness increased, thermal efficiency increased.
Heat Transport in Groundwater Systems--Laboratory Model
(Texas Water Resources Institute, 1980-08) Reed, D. B.; Reddell, D. L.
Solar energy is a possible alternate energy source for space heating. A method of economic long term solar energy storage is needed. Researchers have proposed storing solar energy by heating water using solar collectors and injecting the hot water into groundwater aquifers for long term energy storage. Of paramount importance to the success of such a system is the quality and the behavior of the aquifer used for hot water storage. In general, the problem is to obtain an accurate prediction of the response of an aquifer system and its basic components to the operation of a system of injection and pumping wells which are transporting water at a notably different temperature than the natural groundwater. The injection of hot water into a groundwater storage system will have a pronounced effect on the specific storage and mass flow within the aquifer. These effects will result from differences in viscosity, density, specific heat, and thermal conductivity between the injected water and the natural groundwater. A complex system of energy and mass transport will result, making analytical solutions unattainable or very complex. The objective of this study was to develop a numerical simulation which would predict the pressure and temperature of water in a groundwater system at any time in response to the pumping and injecting of hot and cold water. A numerical model was developed in which the groundwater flow equation and the energy transport equation are solved simultaneously using a finite difference approximation for the time derivative and three-dimensional Galerkin-finite element approximations for the space derivatives. The use of a strict Galerkin approach led to unacceptable solution oscillations in sharp temperature front problems (i.e., problems where the temperature changes quickly over a small distance or time). Several techniques were tried in an attempt to correct the problem. Reduction of element and time step size proved ineffective in eliminating the sharp temperature front oscillation problem. An upstream weighting scheme corrected the oscillation problem, but resulted in an unacceptable smear of the sharp temperature front. A mass lumping scheme resulted in the best solution to sharp temperature front problems. The mass lumping scheme yielded solutions without the oscillation problem and with less smear than the upstream weighting scheme.
Optimal Use of Groundwater and Surface Water to Reduce Land Subsidence
(Texas Water Resources Institute, 1980-08) Acosta-Gonzalez, G.; Reddell, D. L.
Response of Peanuts to Irrigation Management at Different Crop Growth Stages
(Texas Water Resources Institute, 1980-12) Dahmen, P.; Newton, R. J.; Brown, K. W.; Reddell, D. L.; McFarland, M. J.; Howell, T. A.
Past irrigation research on peanuts has shown that when the plant is exposed to soil moisture stress at different crop growth stages, different responses seem to exist between the Spanish and the Florunner peanut varieties. The Spanish peanuts appear more susceptible to soil moisture stress during the blooming and pegging stage, while the Florunners seem more susceptible during the late maturation stage. The objective of this experiment was to determine the optimum irrigation schedule for peanuts at different crop growth stages for the Spanish and the Florunner varieties. The yield of the two varieties was evaluated under seven different irrigation treatments including a "no stress" check treatment and a dryland treatment. Each treatment had a different schedule of either irrigating or stressing the peanut plant during one or more of three crop growth stages. The three crop growth stages were: (1) pegging; (2) early maturation; and (3) late maturation. Rainfall during the vegetative and blooming stage ensured adequate moisture for both of the crop growth stages. Evapotranspiration was monitored throughout the life cycle for both peanut varieties. The evapotranspiration was determined using a soil moisture balance equation. Plant growth in the form of dry matter accumulation and leaf area index was also studied for the Spanish variety. No significant differences in the leaf area index existed between the treatments. The dry matter growth analysis showed that an irrigation during the pegging stage resulted in a faster pod weight accumulation during the early maturation stage than if no irrigation occurred during that stage. The yield and evapotranspiration results showed that differences existed between the two peanut varieties. First, for the Spanish variety, the results indicated that soil moisture is needed during the pegging stage to obtain near maximum yields. Treatments with an irrigation during the pegging stage had a greater evapotranspiration and larger yields, than the treatments without an irrigation during this stage. Second, if an irrigation is made during the pegging stage, an additional irrigation during the early maturation stage is unnecessary. Third, an irrigation during the late maturation stage will increase yield if dry climatic conditions normally exist during this stage. In the case of the Florunner variety, the yield results indicated that moisture stress should occur in no more than one of the crop growth stages if yield reductions are to be minimized. Also, an adequate supply of soil moisture during the late maturation stage is absolutely necessary in order to obtain maximum yields for Florunner peanuts. Treatments which had an irrigation during the late maturation stage had a steady evapotranspiration rate during this crop growth stage and had near maximum yields. Treatments which showed a decrease in the evapotranspiration rate during the late maturation stage produced a significantly lower yield.
Single Location Doublet Well to Reduce Salt-Water Encroachment: Phase I-Numerical Simulation
(Texas Water Resources Institute, 1983-09) Reddell, D. L.
C. E. Jacob received patents in 1965 for a single location well doublet that would produce fresh water overlying salt-water without upconing of the heavier salt-water and pollution of the fresh water zone. No known evaluation of the concept or development of design criteria has been accomplished. In this study, a finite difference radial flow model was developed to determine groundwater velocities and salt concentration as a function of time and space. This model was verified and is available for evaluating design criteria for Jacob's single location well doublet. Initial runs with the model indicate that the concept has potential, particularly in aquifers with clay lenses in the salt-water zone. Additional runs with the model will be needed to fully establish the design criteria necessary for Jacob's single location well doublet.