Subsurface dyke
Encyclopedia
A subsurface dyke is a barrier impermeable to water that is placed underground to control the groundwater
flow in an aquifer
, and to raise the water table
.
constructed at Krishi Vigyan Kendra, Kannur at Panniyur near Taliparamba
under Kerala Agricultural University
with the support of ICAR
as part of demonstrating rain water harvesting
technologies has become a living example for an effective method for ground water conservation. The success story of the sub-surface dyke has demonstrated that it is one of the most feasible methods for the conservation and exploitation of the ground water resources of the state. The dyke is now the largest rainwater harvesting system in the region.
.
in 2007 to solve the problem of water scarcity. The experience of KVK indicated that subsurface dyke was an efficient barrier to arrest the subsurface flow of water and conserve ground water. The rate of depletion of drainable water in the catchment area due to the typical undulating topography could be efficiently arrested by the dyke. The dyke resulted in the maintenance of higher water table in the catchment area for a longer period of time. There is an existing dug out pond with top length of 12 m, width 8m a depth 5m in the upstream side of the dyke. The pond is the only source of water in the KVK farm. The pond, which usually gets dried up in the summer is now maintaining a high water table throughout the year as the dyke ensures an incessant supply of water to the pond. Weekly data on the ground water level were recorded using water level recorder. The data showed that significantly higher level of water table was maintained in the catchment area (upstream area) compared to down stream area. Taking into account the mean depth of soil as 2 m the catchment area as 1.5ha
(the actual area is 15 ha) and the drainable porosity as 10%, the total water storage capacity of the dyke would be 3000 m3. The crops cultivated in the catchment area would be benefited by way of constant capillary feeding of the rhizosphere. Kerala receives, on an average, more than 3000mm of rainfall per annum which is concentrated to the months of June to October. Due to the typical undulating topography of the state, the excess rain received is mostly lost through runoff. Immediately on cessation of rains subsurface water drains off along the slope resulting in poor retention of water in the catchment area. In spite of the heavy rainfall received in Kerala, the state experiences severe drought during summer months due to inefficient utilisation of rain water. In a state like Kerala
, where the pressure on land is very high surface storage of water in large reservoirs with their adverse ecological impact is not an economic proposition. Alternatively, structures like subsurface dyke are most ideal for in situ conservation of rainfall received in a watershed.
technologies demonstrated at KVK include stone pitched contour bunds, dry rubble check dams, protection of seasonal spring by afforestation, moisture conservation pits, sprinkler and drip irrigation and roof water harvesting system.
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
flow in an aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
, and to raise the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
.
Introduction
Although the total amount of water on Earth is generally assumed to have remained virtually constant, the rapid growth in population, together with the extension of irrigated agriculture and industrial development, are putting stress on the quality and quantity aspects of natural system. The sub-surface dykeLevee
A levee, levée, dike , embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels...
constructed at Krishi Vigyan Kendra, Kannur at Panniyur near Taliparamba
Taliparamba
Taliparamba is a city and a municipality in Kannur district in the Indian state of Kerala and spread over an area of 43.05 km2. It stretches from the coastal area of Ramanthali to Nuchiyard and Vayathur villages, touching the Karnataka border.Taliparamba is a big town of 67,000 people...
under Kerala Agricultural University
Kerala Agricultural University
Kerala Agricultural University is the primary and the principal instrumentality of the Kerala state in providing human resources, and skills and technology, required for the sustainable development of its agriculture, defined broadly encompassing all production activities based on land and water,...
with the support of ICAR
Icar
Icar is a free science fiction role-playing game designed and published by Rob Lang. Icar was first created in 1990 by Robert Lang by viewing others playing RPGs at the Finchley Games Club. Although most of the content is created by Robert Lang, the game is supported by a close knit team of play...
as part of demonstrating rain water harvesting
Rainwater harvesting
Rainwater harvesting is the accumulating and storing of rainwater for reuse before it reaches the aquifer. It has been used to provide drinking water, water for livestock, water for irrigation, as well as other typical uses. Rainwater collected from the roofs of houses and local institutions can...
technologies has become a living example for an effective method for ground water conservation. The success story of the sub-surface dyke has demonstrated that it is one of the most feasible methods for the conservation and exploitation of the ground water resources of the state. The dyke is now the largest rainwater harvesting system in the region.
What is subsurface dyke
Subsurface dyke is a structure that is built in an aquifer with the intention of obstructing the natural flow of ground water, thereby raising the ground water level and increasing the amount of water stored in the aquiferAquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
.
How the dyke is made
A trench was made across the valley portion of the undulating topography of the farm down to the bed rock. Three layers of plastic sheets were spread on the wall of the trench from ground level to the bed rock level. The plastic sheet on the wall measured 40m in length with a maximum depth of 8 m. It obstructs the flow of sub surface water raising water table in the catchment area.Benefits
The dyke was constructed in the 25 hectare farm of Krishi Vigyan Kendra KannurKrishi Vigyan Kendra Kannur
- Brief history : is a front line agricultural extension center financed by the Indian Council of Agricultural Research . It became functional since 30-03-2004 in the premises of Pepper Research Station, Panniyur under Kerala Agricultural University...
in 2007 to solve the problem of water scarcity. The experience of KVK indicated that subsurface dyke was an efficient barrier to arrest the subsurface flow of water and conserve ground water. The rate of depletion of drainable water in the catchment area due to the typical undulating topography could be efficiently arrested by the dyke. The dyke resulted in the maintenance of higher water table in the catchment area for a longer period of time. There is an existing dug out pond with top length of 12 m, width 8m a depth 5m in the upstream side of the dyke. The pond is the only source of water in the KVK farm. The pond, which usually gets dried up in the summer is now maintaining a high water table throughout the year as the dyke ensures an incessant supply of water to the pond. Weekly data on the ground water level were recorded using water level recorder. The data showed that significantly higher level of water table was maintained in the catchment area (upstream area) compared to down stream area. Taking into account the mean depth of soil as 2 m the catchment area as 1.5ha
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
(the actual area is 15 ha) and the drainable porosity as 10%, the total water storage capacity of the dyke would be 3000 m3. The crops cultivated in the catchment area would be benefited by way of constant capillary feeding of the rhizosphere. Kerala receives, on an average, more than 3000mm of rainfall per annum which is concentrated to the months of June to October. Due to the typical undulating topography of the state, the excess rain received is mostly lost through runoff. Immediately on cessation of rains subsurface water drains off along the slope resulting in poor retention of water in the catchment area. In spite of the heavy rainfall received in Kerala, the state experiences severe drought during summer months due to inefficient utilisation of rain water. In a state like Kerala
Kerala
or Keralam is an Indian state located on the Malabar coast of south-west India. It was created on 1 November 1956 by the States Reorganisation Act by combining various Malayalam speaking regions....
, where the pressure on land is very high surface storage of water in large reservoirs with their adverse ecological impact is not an economic proposition. Alternatively, structures like subsurface dyke are most ideal for in situ conservation of rainfall received in a watershed.
Ideal location for the dyke
The ideal location for the dyke is a well defined, wide, greatly sloping valley with a narrow outlet having limited thickness of loose soil or porous rock on the top with massive or impervious rock below . Subsurface dyke has many advantages. It does not require additional surface reservoir. There is no loss of agricultural land. There is minimum evaporation loss since the storage is subsurface. There is no siltation and loss of reservoir capacity. The cost of maintenance is negligible. It is environment-friendly.Other water harvesting technologies
The other rainwater harvestingRainwater harvesting
Rainwater harvesting is the accumulating and storing of rainwater for reuse before it reaches the aquifer. It has been used to provide drinking water, water for livestock, water for irrigation, as well as other typical uses. Rainwater collected from the roofs of houses and local institutions can...
technologies demonstrated at KVK include stone pitched contour bunds, dry rubble check dams, protection of seasonal spring by afforestation, moisture conservation pits, sprinkler and drip irrigation and roof water harvesting system.