One-dimensional Drainage of Soil ProfIle with Root Extraction

A one-dimensiunal n1l1nrncalmodel was developed to solve an unsaturated flaw equation for a soil prafik that represents a soil-plant-water system with a shallow water table above an impermeable layer. The diffusivity form of the Richard's equation was solved using Crank Nicalson implicit finite difference scheme and a general Newton-Raphson interative method. The model was used to simulate volume tric moisture content, capillary pressure, and position of water tab. It was also used to simulate the cumulative soil water depltion" within" the soil profile. Result from the compare model compared re compared reasonably we" measured lysimeter data

Basin water management

Presented at Contemporary challenges for irrigation and drainage: proceedings from the USCID 14th technical conference on irrigation, drainage and flood control held on June 3-6, 1998 in Phoenix, Arizona.Includes bibliographical references.The required level of management of the fresh water supply practiced within a given watershed is defined by all of the physical, chemical, economic, environmental, and sociological factors involved. Efficiency of water use, consumptive versus non-consumptive utilization of water, diversion requirements, and environmental requirements all need to be understood and balanced to optimize use of the available water. Where watersheds span states and sovereign nations, treaties and agreements are required for orderly use of the fresh water resource. Understanding of the nature of water use and the hydrology of the water resource system is a key element in rational utilization of the resource. Elevation, water quality, and temporal availability are some of the parameters that must be considered. Ground water and surface water need to be treated as a single resource for effective management

Simplex Algorithm for Optimizing Drainage Design

A methodology and computer model is developed to determine economically optimum closed subsurface drainage systems in irrigated areas. The model maximizes net benefits, by comparing profit driven by crop yield to drain system cost and selects an optimum drain layout. The optimization methodology used, is the SIMPLEX method, Neider and Mead. The SIMPLEX model was linked to the subsurface drainage model DRAINMOD Skaggs [10], and to the surface hydraulic model KINE, Walker and Skogerboe[14]. The selected optimum drainage system maximizes the difference between total revenue, and the total cost of installation, operation and management of a particular drainage system. The optimization sub-program provides a workable and simple procedure for optimizing water management simulation models

Impact of Water and Soils Having High Source-Sink Potentials on Water and Salinity Management Under Irrigation in the Upper Colorado River Basin

Water management in irrigation projects is one potential method for reducing downstream salinity in the Colorado River. An important contribution can be made to developing more effective irrigation water management practices for water conservation and salinity control through identification and better understanding of the soil and water interactions that result in soils behaving as salt sources or as salt sinks. The interactions identified in this study were examined to determine the effects of various management alternatives on the quality and quantity of salt in subsurface return flow from irrigation projects. A soil solution chemistry model was developed to describe the soil-irrigation water interactions. The model includes the effect of cation exchange capacity. The model was calibrated and checked with data obtained from lysimeters. A water management model that contained a soil solution chemistry component was calibrated for the Ashley Valley of Utah and was used to determine the sensitivity of stream flows and salinity to irrigation water management alternatives. The source-sink behavior of soils was found to depent on water quality, residual soil salinity, and water management practices. The key relationships are described. In applying these relationships, site specific conditions must be examined to determine the effectiveness of proposed irrigation management changes that are expected to affect downstream salinity

Unsaturated Transient Flow Through Heterogeneous Soils: Numerical Solutions and Analyses of Three-dimensional Axisymmetric Flows

This study deals with unsaturated, unsteady water movement through hetergeneous porous media. The specific problem investigated is the transient three-dimensional sxisymmetric flow resulting from water being applied on a horizontal circular area. The heterogeneity of the soil is described by allowing any or all of the five parameters in the Brooks-Corey equations to be any continuous function of depth. Methodologies for obtaining numerical solutions to the resulting nonlinear partial differential equation and its associated initial-boundary value problem have been developed an dimplemented in a computer program. The numerical solution is based on the Crank-Nicolson method of finite differencing and the solution to the resulting system of non-linear algebraic equations for each time step is by the Newton method combined with the line successive over-relaxation (LSOR) method. The numerical solutions provide the follwoing at each time step used: (1) the distribution of soil water saturation throughout the region, (2) the distribution of capillary pressure throuout the region, (3) the distribution of hydraulic head throughout the region, (4) the rate of infiltration if the area of application is specified at a given moisture level, (5) the extent and amount of lateral and vertical water movement, and (6) the rate of advance position of the wetting front. The solutions resulting from various variations of linearly specified heterogeneities have been studied and their influence of such quantitites are infiltration rate or intake capacities and wetting front movement, have been analyzed. To determine the effects of lateral water movement, solution results from the axisymmetric solutions have been compared with solutions from a one-dimensional vertical flow model that permitted the same specification of heterogeneity. A number of graphs are presented that illustrate influences of different soil hetergeneities. Coaxial graphs were developed to summarize the results of a number of solutions that relate the different in infiltration in hetergeneous and homogeneous soils to the variations of the five parameters in the Brooks-Corey equations. The numerical solutiosn are verified with reasonable agreement with field data at the Reynolds Creek experimental watershed obtained from experiments which duplicate the geometry of the mathematical model clostely, if not the heterogeneity, also

PRACTICAL LAND GRADING BASED ON LEAST SQUARES.

Practical methods for land grading design of a plane surface for rectangular and irregularly shaped fields based on a least squares analysis are presented. The least squares procedure leads to a system of three linear equations with three unknowns for determination of the best-fit plane. The equations can be solved by determinants (Cramer's rule) using a procedure capable of solution by many programmable calculators. The detailed computational process for determining the equation of the plane and a simple method to find the centroid location of an irregular field are also given. An illustrative example and design instructions are included to demonstrate the application of the design procedure