I have attached pictures taken on 15th March at my farm after attempting to excavate some earth to test for water sources. We could get water at around 4-6ft depth as seen in the picture. This is a low-lying field which used to be cultivated for paddy a decade ago but left fallow for many years.
The soil structure is very loose and I am not sure the bunds will be able to hold one monsoon season and may dissolve and collapse as water saturates. Attached are some pictures of the bund created on 1st day with the excavator. The water in the picture is ground water source and it has not rained in this region for the past 3-4 months. The excavation is for ground water source and not for rain water storage, since the soil is not good at holding water and it tends to seep in rather than stay above ground.
I am advised by the contractor that it is risky to go full scale with the pond idea and even a stone pitching work has a high risk of collapsing in heavy monsoon. This is located in Karkala/Udupi region which gets heavy thunderstorms in monsoon. The contractor is advising to go with a 15-20ft well instead of using Karkala black granite rocks sources from quarries nearby. The overall cost for such a construction would be 8-12 lacks with skilled labout for well and unskilled labour for pond lining.
My question to the community is that if it costs me 10 lakhs to build a well of 25ft dia and 15ft depth, should I go for it or spend the same amount on the open pond of roughly 60-100 ft dimensions? Is the risk of the pond wall collapsing due to soil water saturation in peak monsoon a real threat? What do the learned and experienced folks in this forum have to say? The area already had 6 failed borewells (by the previous owner of the property) before he gave up and sold the land to us. Water diviners seem to fail since the area has Karkala sheet rock subsurface at many spots.
I have 2 people advising to go for a shallow but wide pond with sloping and stepped walls pitched with stones, and 2 others advising for a well not more than 25ft in diameter. Both approaches require a significant investment of time and money. I need to decide soon since the work has to be finished before the onset of the monsoon in the first week of June.
It will not a Perennial supply. In summer you may not have water.
Enlighten me the Purpose of Water. It is for Farming , You may hve the Water during Rainy season. If you want to go for Summer crop , you should have to go further depth. Have you got Ground Water Survey? If so what is the Report. Please Share the Report.
Based on the available information available,
The site has no underground water spring because of sheet rock, except availability of seepage water, of which availability goes down as the summer advances and also if some one draws this seepage water in the down stream.
With this seepage water condition, except paddy, no ID Crop will be successful.
If this seepage water source is dependable even in dry periods, an attempt can be made to open drains all around the plot (if it is a big plot, at 100 to 150 meter apart cross wise also), to improve sub-soil Ill drain conditions. Connect these drains to a swallow sump of 5 m depth at the lowest portion of the plot, to have a water body of 5 to 10 sq m, based on the water requirement of the crops planned.
Deep Wells or Filter Point may not be possible, because of the collapsible nature of soil.
Use of In-Well Submersible Pump may be better.
Deepening on the well may be done, based on the water requirement & as the water table goes down.
More than one swallow pod may be planned based on topography of the area and water requirements.
Please note that the soil of the area be sandy, may have poor fertility, as seen based on the collapsing nature of the well side wall.
Improvement of soil structure and OM & OC may have to be improved, before planning for any crop.
What is the purpose of this well or pond? What crops you have in mind?
A: To secure some surface water source before locating bore points. Plan is tree-based farming in the long term in a staged manner. Not planning to grow anything with high water demand until a good borewell is secured.
Do you have any streams or ponds or canal or river nearby this land?
A: Not at least in the 5-10 km radius.
Instead of permanent channels or trenches, it is possible to lay specially made porous pipes, often with geotextile covering, to transport water in the soil profile by gravity. The pipes are typically laid along the slope about a meter below surface and the trenches are covered with soil. You can move the water to a deeper level pond as @Pamidi has suggested.
Generally this is done to address water logging and resultant salinity/sodicity problems. We got this done in some of our farm a couple of years back.
Typical installation cost is about 50k per acre - depends on a lot of factors including pipe spacing. The pipes are available from Jain Irrigation, among others.
We decided to pause work for a week to observe the water behavior. Attached is the pic from day 3 after excavation. The water level has risen 4 inches and the surrounding areas are mostly dry due to sun exposure.
A ground water forms above an impervious layer, either a rock or clay layer when there is percolation of rain water or subsoil flow from higher ground water sources. There is a basic rock layer at the very bottom, but often there are Perched Water tables ( river, ground water, perched water table (wikipedia) ) formed by relatively impervious layers in the vadose or unsaturated zone. Your land was paddy field earlier; it means there was, and probably is, a clay layer roughly 4-6 feet (120-180 cm) shown by the ditch you JCBed. deep in the form of bowls in the paddy field. When the rains fall, all these bowls get filled, the rice field looks like a pond and the rice seedlings (not the rice seeds) are planted in the field. Keralites call this âJnaru nadalâ, what is it in Kannada? In normal rains water will flow or drop into the rice field and will flow out maintaining a rice field water level. Extreme rains and resulting floods may wash out rice fields.
So in your fallow rice field, the bore wells must have cut through the perches, guessed by me at 1.8 m depth. It will not find any water beneathe the perch; maybe you have to go down to the primary Ground Water level at your area (this data will be available from the Central Ground Water Board). Let us say that the Ground Water Level is 10 m deep and the bed rock is 22 m deep. So the saturated zone is of height 12 m. A bore well or open well will have to be dug down to roughly 16 m.
Now about the pond. If your pond is more than 1.8 m deep, say 4 m, it will not be able to store water. Or you will have to create a perch at the bottom of the 4 m deep pond. TN farmers insulate their ponds with 500 micron HDPE plastic geomembrane. (1.8m x 1.8m heavy duty geomembrane sheet costs around Rs 800).
Easiest appears to be a less than 1.2 m deep pond with natural clay perch at roughly 1.8 m. But you may not be able to pump water from this small area shallow pond to irrigate large area. Suggest an open well 4 m deep, 1 m diameter insulated with 500 micron HDPE geomembrane from 1.8 m to 4m on the side and on the bottom.
Vinod Kumar
Diploma in Watershed Management, IGNOU
Institute for Watershed Development and Management â Kerala
Thanks Vinod for your time and valuable advise.
So if I read you correctly, you are essentially stating we test how deep the aquiclude is which is bowling this water above the real ground water table and compare it with ground water depth of surrounding area.
Could you please explain why you recommend HDPE liner for a well of 12-15ft depth? Is this to hold off muddy water percolating from the sides from the upper layer perch?
Keeping the width to 1m vs 6m in the pic above. What are pros and cons beyond the cost saving of the wall lining due to reduced circumference.
So if I read you correctly, you are essentially stating we test how deep the aquiclude is which is bowling this water above the real ground water table and compare it with ground water depth of surrounding area.
Yes, we have to find the shape and position of the perch or aquiclude; but we do not need info about the primary ground water level here or surrounding. We should try to seal any holes in the perch, avoid destroying the perch or its bowl shape. We should compare the perched water table depth with neighbouring perched water table depth to identify the continuity of the perch. The primary ground water level can be measured, especially after rains, to find whether the perched water will be charged by rising primary ground water. Most of the open wells in Kerala, and even rivers, show high water level after rains or irrigation. But the well water level often falls to the bottom within a week of departure of rain. The rivers too fall below the sand, if there is any sand left. This quick fall of the perched water level is due to the damaged perches. We âcleanâ the temple ponds by removing the dirt below, but then we remove the clay layer, the perch; no wonder the ponds dry up in summer or after excess pump out. TN farmers created a synthetic perch by sealing the pond with HDPE geomembrane.
Could you please explain why you recommend HDPE liner for a well of 12-15ft depth? Is this to hold off muddy water percolating from the sides from the upper layer perch?
No, not to prevent muddy water from seeping in; the HDPE geomembrane at the sides and bottom of the well is to prevent the stored water from percolating away; just like TN farmers save water in their ponds by lining it with HDPE geomembrane. The source of water for the well is the perched water table, not the primary ground water. The 4m deep, 1 m dia âwellâ looks more like a water storage tank; underground and not on rooftop. The âwellâ should have rings with lateral holes above the perch where water from the perched water table can seep in; surrounding the rings, sand and small rocks can be placed to prevent the mud from entering.
Keeping the width to 1m vs 6m in the pic above. What are pros and cons beyond the cost saving of the wall lining due to reduced circumference.
Bore wells are around 10 to 15 cm diameter. But the pumping out rate would be low. Open wells are constructed using RCC rings. Standard 100 cm diameter RCC ring of height 60 cm and wall thickness 5 cm costs around Rs 500/. A 4 m well with 1 m dia rcc ring has a volume of 2.5 m^3 (2500 litres). Wouldnât it be sufficient for pumped irrigation? The cons of the geomembraned well or underground water tank are 1) water from the primary ground water source does not seep into the well, 2) HDPE geomembrane inside the 4 m deep well or water tank is more difficult than the flat linings on a pond. 3) the mud from the perched water table could fill up the underground âwater tankâ; the mud accumulates even in rooftop water tanks; I use siphoned brushes to clean my rooftop watertank at least once in 6 months.
We should compare the perched water table depth with neighbouring perched water table depth to identify the continuity of the perch.
The perch seems to be 1 field wide, approx 75 * 150 ft in dimensions. THe adjacent fields do not show signs of water like the field we chose. I am yet to dig a trench to verify this. This is the last field in our holding, and this is where we see high water level and not in the previous or immediate next although it is slightly lower placed due to the terrain sloping.
Most of the open wells in Kerala, and even rivers, show high water levels after rains or irrigation. But the well water level often falls to the bottom within a week of departure of rain.
Fortunately, the water is still holding in this case. The last rain must have been in November if I recollect.
Instead of Going for Open Well , it is advisable to go for pond with Plastic/ Asbalt lining in the LOWLYING Area in Your Land while filling up of the Pond during Rainy season. The seize of the Pond be based on your Land Area and Rain shedding in your area.
If you seek advise we can Provide our Consultancy service after receiving the full details.
We observed the water pattern in this area and decided to go with a pond of approx 10-12 feet depth depending on where and at what depth we hit the rock sheet. As Mr Vinod explained above, this is a perched water table and not standard ground water (which is generally at 17-22ft depth in the area. For this season we will go wide with gentle slope to observe how the soil holds during heavy rains and line the bunds with deep rooting plants as against any external engineering. The downside would be muddy water for first couple seasons, and we are okay with it as long as the sloped bund holds.
Itâs a tough decision between a well and an open pond for your farmâs water source. Considering soil conditions and past failures, a well might offer more reliability, but at a higher cost. An open pond could be cheaper but risks collapse during heavy rain. Consulting local experts familiar with soil and hydrological conditions could help you make the best choice. Act swiftly to complete the project before the monsoon in June. Best of luck with your decision!
Yes, we are simultaneously investing in a open well at the center of the property. There used to be a open well in that location (like 25-30 years ago) we are digging this currently. An expensive affair, but securing some water source is a priority.
