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Possibility of implementing the vertical drainage network
2023-06-25
Dr. Ehab Mohammed Al-Shabani
Ministry of Agriculture – Agricultural Research Department
Preface:
The main objective of the drainage of all kinds is to get rid of excess water and maintain an appropriate groundwater level to balance between the moisture content and the water content in addition to the salt content in the root zone, which is recognized in reducing the level of ground water (groundwater) and maintaining the required level is the drainage method by open channels or schemes. The recognized method of lowering the level of ground water (groundwater) and maintaining the required level is the method of drainage by open channels or schemes, but this method is not the only one currently used to reduce the level of ground water for various purposes, as the vertical drainage method (vertical drainage) or which is also called drainage by wells (drainage by pumping) can be used to perform the same purpose, This type of drainage is summarized by pumping groundwater from the water-bearing layer (aquifer) by wells with certain specifications prepared for this purpose, and this pumping process leads to a reduction in Eritrean pressure (artesian), which in turn causes the movement of ground water (phreatic water table) downward. The available experience in the use of the vertical drainage method is low compared to the traditional drainage method, as this method was used for the first time in the United States of America in 1918 to serve some waterlogged lands and was also used in western Pakistan to control groundwater and soil salinity in the region, in addition to its use in the Uzbekistan region and the Ararat plains in the Soviet Union in 1926.
In Iraq, several pioneering experiments have been conducted on the use of this type of drainage networks in the basin of the bottom of Khalis and the area of Al-Fadiliya near Baghdad and in the marshes, where they proved their efficiency to perform the required purpose under the conditions of that region. Drainage in general, whether it is of the traditional type (horizontal) or vertical (by wells), mainly aims to reduce the ground water level in the waterlogged areas and maintain a certain level of ground water below the soil surface so that the topsoil conditions are good, whether for agricultural purposes or others. Bad conditions result either from the presence of bad drainage conditions, whether natural or artificial, or from the presence of perfusion (leakage or oozing) from a nearby water source, or when the rainfall is so high that it is difficult to get rid of it quickly, these conditions make the movement of machinery and heavy ones very difficult due to the fact that the strength of the soil to withstand the pressure applied to it is significantly reduced when the moisture content in the soil increases, and when the groundwater level is less than (0.6 m).
First: Conditions to be met by the use of vertical drainage:
There are some conditions that must be available in an area so that the use of a vertical drainage system is logical and reasonable, but as we mentioned previously, choosing the appropriate system depends on the special circumstances and the objectives pursued from them:
1. The water-bearing layer should be sufficiently deep, as homogeneous as possible, and transportable
2. Relatively high transmissibility, which allows pumping adequate amounts of groundwater.
3. There must be a connection between the free groundwater near the earth's surface and the water in the water-bearing layer.
4. . To prolong the life of the well, the soil or water must not corrode the materials from which the parts and accessories of the well are made.
5. In the fact that the groundwater has high salinity, it is necessary to study the possibility of avoiding the damage resulting from the pumping of groundwater on the surrounding areas.
Second: Characteristics of Vertical Drainage :
1. In the vertical drainage system, the loss of land areas is very little compared to the regular drainage system, and the network of wells does not constitute any obstacle to the movement of machinery or sapling, as caused by open drainage channels, which usually act as field complexes for covered drains.
2. In vertical drainage, the ground water level and the required depth can be controlled, mainly depending on the hydro geological conditions in the area and the pumping rate from the well.
3. The vertical drainage system and the method of its application in the undulating ground are more economically feasible than the traditional drainage method because there is no need to dig large amounts of earth from high areas.
4. In cases where the deep layers of the soil are more permeable than the upper (surface) layers, the use of vertical drainage is the only optimal method for the purpose of taking advantage of such appropriate hydro geological conditions.
5. The maintenance cost of the opening pipe system in the vertical drainage is lower compared to the cost of maintenance of open and covered drains and drainage channels.
6. The use of vertical drainage to lower the ground water level lies in small or confined areas where the traditional drainage system cannot be used.
Third: Determinants of vertical drainage :
1. The vertical drainage system is a complex engineering structure compared to the traditional drainage system.
2. Some cases of water logging as a result of unexpected heavy rains require the existence of a dense well system for the purpose of lowering the ground water level at the required speed.
3. The successful use of vertical drainage s depends on the appropriate properties of the water-bearing layer, so that the transmissibility of this layer is high, and in the event that the water-bearing layer is actually semi confined, the upper layer must have a low hydraulic resistance, which requires knowledge of the properties hydro geologist carefully before deciding to use vertical drainage .
4. Vertical drainage is not economically feasible when used to drainage small areas due to groundwater runoff from neighbouring areas.
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