Abstract:This study is aimed at quantifying the difference in aquifer's response to recharge between some different locations in a fan aquifer and a delta aquifer for a preliminary study of revealing mechanisms of water transport in alluvial aquifer. The aquifer's response to recharge is statistically quantified with the two viewpoints: (1) timing and volume of recharge and (2) time length of aquifer's holding water. For the first point, a statistical model that links precipitation and groundwater level is introduced, and its parameters are identified using correlation analysis. Our results show that the recharge rate at the toe is higher than that at the apex and at the delta. For the second point, the concept of 'memory effect' of aquifer is adopted and quantified using the autocorrelation and spectral analyses. Our results show that the memory effect is longer at the toe of fan than at the apex, and thus, a temporary increase of water level has about five times as long-term influence on subsequent water levels at the toe of the fan as at the apex. This study demonstrates that the statistical analyses and modeling of hydrological data are useful for characterizing aquifer's hydrodynamics.

No abstract

No abstract

An optimization model for cropping-plan placement on field plots is presented for supporting decision-making on agricultural management by a farming organization. The mixed 0-1 programming technique is employed to select the next planting crop at each field plot in a holistic manner. Reduction of total nitrogen discharged from field plots to the downstream end of the drainage canals is expressed as an objective function of the model to balance an achievement of economic goal and environmental conservation. Some Japanese governmental policies on regulating rice cropping areas and on promoting production of particular upland field crops can be formulated in the model. A computational example of cropping-plan placement on field plots managed under integrated policies is given by operating the optimization model with various weights associated with the objectives. The procured tradeoff curve and corresponding patterns of cropping-plan could be useful in the decision-making by the farming organization.

Paddy farming is the cause of water pollution in many parts of the Asian monsoon district As a primary study fbr strategically rnanaging Tiyer water quality on a watershed scale, the dynamics of nenpoint source polLutant loadillgs from paddy farrning area are examined for a selected agricultural watershed where a river runs through and rice paddies take greater part of the farrnland. A total of 122 outfal]s at which drainage (inigation runoff) waters enter the river are exactly identifiable along the whole course of the river. Results of the detailed surveys of drainage waters, conducted at typical stages in an indigenous calendar of paddy farming practice (CPFP) in an irrigation season as well as at a few stages jn the off-season, are analyzed. Major findings are as follows. (I) Any of the CODMn, N03-N, 1[LN and TLP loadings totalized over al1 the outfa11s is maximized in puddling and transplanting with basal fertilizer application, (2) The co]centrations of N03-N and TLN. averaged over all the outfa11s, are rather low during the irrigation period of mid April to early September. Nevertheless the loading arnounts of them remain high during the sarne period, relatively close]y correlating with the amount of outfal1 discharge. (3) Tbpdressing the paddies in the booting stage of rice causes a distinguishable extra load of N03-N. (4) The dynamics of the CODM. and TLP loadings are totally different from those of the N03-N and TLN loadings, taking straightfofward declines frorn their maximums or being significantly restricted by their concentratiens rather than by outfall discharges.