CALCULATION OF DISTANCE BETWEEN DRAINS USING ENDRAIN PROGRAM PUBLISHEDRares Halbac-Cotoara-Zamfir
EnDrain program, realized by Prof. Oosterbaan (Netherlands), computes the distances between drains and also determines shape of water-table level of by using the formula of flow’s energy balance. Oosterbaan, Boonstra and Rao (1994) introduced the energy balance of groundwater flow. It is based on equating the change of hydraulic energy flux over a horizontal distance to the conversion rate of hydraulic energy into to friction of flow over that distance. The energy flux is calculated on the basis of a multiplication of the hydraulic potential and the flow velocity, integrated over the total flow depth. The conversion rate is determined in analogy to the heat loss equation of an electric current. By using EnDrain program we can compute the flow discharged by drains, the head losses and the distance between drains also obtaining the curve described by water-table level. These calculations are necessary to design a drainage system in the frame of an irrigation system for water-table control, salts control and respective for soil’s humidity control. The calculation of distances between drains is based on the concept of underground flow’s energy balance. There also used the traditional concepts based on theories of Dupuit, water balance and mass conservation. The program allows the utilization of three different soil layers, each of them with their own permeability and hydraulic conductivity, on layer being above and two layers below drains level. The energy balance of groundwater flow developed by Oosterbaan, Boonstra and Rao and used for the groundwater flow in unconfined aquifers, is applied to subsurface drainage by pipes or ditches with the possibility to introduce entrance resistance and/or soils with anisotropic hydraulic conductivities. Owing to the energy associated with the recharge by downward percolating water, it is found that use of the energy balance leads to lower water table elevations than when it is ignored. The energy balance cannot be solved analytically and a computerized numerical method is needed. An advantage of the numerical method is that the shape of the water table can be described, which was possible with the traditional methods only in particular situations, like drains without entrance resistance, resting on an impermeable layer in isotropic soils. This paper proves its originality by presenting the results obtained in computing the distances between drains with EnDrain program for some soils with humidity excess from western Romania, and, very important, will present graphs with the shape of water-table level for the analyzed soils.
EnDrain; underground's flow energy balance; water-table level shape