Vertical drains
Introduction
Well drainage is underground drainage using wells.
When agricultural land suffers from saturation or soil salinity, pump well drainage (vertical drainage) can alleviate such problems. It is an alternative to drainage through trenches or buried pipes (horizontal drainage).
With an underground drainage system you can lower the water table (or water table) and evacuate salts from the soil so that soil conditions and crop yields are improved.
Design
The vertical drainage system consists of deep wells in a triangular, square, or rectangular network.
The design of the pump well network refers to the depth, capacity, hydraulic discharge, and spacing of the wells.[2].
Well spacing can be calculated with a vertical drainage equation based on the required discharge, aquifer properties (such as depth and permeability), the depth of the well, and the required depth of the water table (or water table).
The basic steady state equation for subsurface flow to wells that completely penetrate a homogeneous aquifer is:[2].
where:.
The radius of influence Ri of the wells depends on the shape of the network and is calculated as:.
where:.
Q secure download is obtained from:.
in what:.
Thus, the basic equation can also be written as:.
With the well drainage equation, several design alternatives can be calculated to arrive at the most attractive solution for controlling the water table on agricultural land.
The cost of the most attractive alternative can be compared with the cost of a horizontal drainage system, which serves the same purpose, to decide which of the two is preferable.
The purely technical design of the well itself is described in[2].
Non-uniform aquifer
The previous basic equation cannot be applied to determine the spacing between wells when they do not penetrate the entire aquifer and/or the permeability of the aquifer is uniform or isotropic. In these cases, a numerical solution of more complicated differential equations is required, and a computer program is needed.[1].
References
- [1] ↑ a b ILRI, 2000, Subsurface drainage by (tube)wells: Well spacing equations for fully an partially penetrating wells in uniform or layered aquifers with or without anisotropy and entrance resistance, 9 pp. Principles used in the "WellDrain" model. International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands.
- [2] ↑ a b c Boehmer, W.K., and J.Boonstra, 1994, Tubewell Drainage Systems, Chapter 22 in: H.P.Ritzema (ed.), Drainage Principles and Applications, Publ. 16, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands. pp. 931-964, ISBN 90-70754-3-39.