Lake water quality management is an extremely complicated problem due to a variety of land use and existence of multiple stakeholders in the watershed. A decision support tool is thus necessary for examining physical, economical and social constraints associated with the management and for coordinating conflicting goals of the stakeholders. In this study, a multiobjective linear programming model is developed for supporting strategic management of lake water quality. Optimal allocation of river-genetic pollutant load is determined to maximize total allowable load into the lake with in-lake water quality standard. The shallow water equations and two-dimensional COD (chemical oxygen demand) transport equation are employed as basic equations to represent physical constraints on COD concentration. In order to consider an economical requirement on equity, the model proactively controls the difference in share of the total allowable load among influent rivers. An optimization example demonstrates that the methodology developed can produce several noninferior solutions (i.e., load allocations) useful for decision-making in lake water quality management.
An inverse method to estimate the unsaturated hydraulic conductivity in seepage flow from field observations is presented. Considering the water movement in soil significantly affected by the soil temperature, the soil column of interest is assumed to be non-isothermal, and therefore the problem is based on coupled 1D water movement and thermal conduction equations. Since the saturated hydraulic conductivity could be definitely known, the inverse problem associated with the unsaturated hydraulic conductivity is reduced to that of identifying the relative hydraulic conductivity (RHC) from the hydro-geological information available. For functional representation of RHC, the free-form parameterized function is employed in lieu of the conventional fixed-form function. Values of the parameters included in the functions are optimally determined according to a simulation-optimization algorithm. For easy application of the method, a utilitarian observation system with simple instrumentation is specially contrived which implements collection of the hydro-geological data relatively easily in-situ available. Validity of the method developed is examined through its practical application to a real soil column in an upland crop field. The results show that the water movement model provides the forward solutions of high reproducibility, when coupled with thermal conduction model and calibrated through identifying the RHC by use of a free-form function.
There are about 2.8 million ha of inland valleys in Ghana and 20 million ha of inland valley in West Africa. Although inland valleys are suitable for lowland rice due to the abundance of water resources and higher soil fertility compared with the upland, they have not been well utilized as agricultural land in West Africa. Further utilization of inland valley for lowland rice will improve the productivity of rice in West Africa. In this study water resources of small rivers in inland valleys in West Africa are evaluated. Two study watersheds with 1,400-1,500mm of annual rainfall in Semi-Deciduous Forest Zone in Ghana were selected and analyzed on slope distribution in the study watershed to grasp suitable area for lowland rice and on hydrological characteristics such as specific discharge and runoff ratio. The following findings are obtained from the study. 1) Most of the rivers in the study watershed are seasonal rivers. Non-flow period of some rivers were shown for around five months from middle of December to early May. However the term of non-flow period varies much depending on characteristics of sub-watersheds. 2) Runoff ratio for 5 years from 2000 to 2004 in Offinso watershed which is a typical watershed in semi deciduous forest zone in Ghana was indicated only 12%. It ranges from 0.08 to 0.16 depending on the year. The monthly runoff ratio indicated little value in March, April and May which is beginning of rainy season and high value in November and December which is beginning of dry season. 3) The gentle slope area with less than 2%, which seems suitable area for lowland rice, occupies 22 % of inland valley.