Skimming Well Technology and Multiple Well Point System

Skimming Wells

¡Skimming well, extract relatively fresh water from the upper zone of the aquifer.

¡The skimming wells are low discharge (less than 28 l.p.s.)

¡Cluster of wells draw groundwater from relatively shallow depth.

¡Skimming wells are for irrigation or drinking water supply purposes.

Types of Skimming Wells

Need of Skimming Wells

¡To get freshwater

¡To manage root zone salinity

¡To reduce energy requirement for low discharge

How to operate a skimming well?

¡Well may be operated for a short period varying from 4-12 hrs.

¡Pumping rate is a crucial decision when to be done for a long term basis.

¡Unregulated pumping often results in the up-coning phenomenon.

1. For ,single-borehole wells with 30-60% penetration depth, 4-28 l/s discharge rates and 4-8 operational hours.

2. Skimming well with 3-6 strainers, well penetration depth 60%,10 l/s discharge and 4 to 6 hours per day of pumping.

3. Continuous pumping deteriorates the pumped water quality.

4. The scavenger wells could provide better quality pumped water

5. Radial skimming wells & Dug wells are not easily adoptable by the farming community

6.Main problems include

¡ well depth,

¡ number of strainers,

¡ deterioration of pumped water quality

¡ reduction in well discharge

7. Farmers use both

l Single strainer 30 m deep wells with 28 to 42 l/s discharge &

l The 15 m deep multi-strainer wells with 4, 6, 7, 10 and 16 strainers and 14-28 l/s well discharge

8. More than 6 strainers will increase cost without any additional benefit.

9.  A the problem involves pumping of groundwater from wells         along with a river plain with geologically saline water.

10. Unplanned pumping results in upconing of saline water.

So, it is necessary to determine optimal locations of fixed capacity pumping wells.

¡  The skimming wells must be operated from optimal locations.

¡   Locations w.r.t space and time to obtain the least saline water.

¡   The salinity concentration is least towards the topmost layer.

Scavenger Wells

¡Skimming well (single‐bore well) is not feasible in aquifer having a very thin freshwater zone.

¡With increase in number of skimming wells, various types of geometrical patterns of different flow conditions are possible.

¡Moreover, the interference of wells causes the drawdown to increase.

¡Combined effect of both these factors is responsible for the up‐coning of brackish/saline water.

       

Case Study 

Multiple wellpoint system for irrigation and drainage in southwestern Punjab (2014)

¡The south-western districts of Punjab are severely affected by waterlogging associated with salinity and alkalinity problems.

¡A thin layer of good quality water is floating over poor quality (brackish) groundwater.

¡A MWPS was designed and developed to obtain good quality groundwater.¡

¡A study was conducted about the status and performance of MWPS.

¡About 41,000 MWPS have been working in the villages of Muktsar, Faridkot and Ferozepur districts.

¡After installation of MWPS

lThe water table depth has been lowered about 1–7 m

lCrop yields enhanced about 10–20% in the year 2012–13

¡The cost of installation of a 4-well point system was computed to be about Rs. 45000 per set

¡The system was found to be technically feasible, economically viable and socially acceptable.

¡The quality of pumped groundwater from MWPS was analyzed and found suitable for irrigation.

Case Study 

Management of brackish aquifers by recharging through multiple wellpoint system (2005)

¡Water table  rose in Faridkot due to:

¡Non-exploitation of groundwater &

¡Excess seepage from canals resulted in.

¡In early 80’s, the water table was at the soil surface.

¡As a result complete soil profile became saline/sodic.

¡The reclamation of the area was initiated through ICAR funded “All India Coordinated Research Project on Agricultural Drainage Under Actual Farming Conditions on Watershed Basis” in the year 1981-82.

¡These aquifers were recharged with fresh/canal water during the monsoon season.

¡It was inferred that the brackish aquifers of the area could be converted into sweet water aquifers.

¡Dug trenches installation was difficult due to high Na content in the soil profile.

¡Therefore, MWPS was invented which was designed, installed experimented.

¡As a result, area became free from waterlogging and sodicity.

¡But the problem of poor quality groundwater was still persisting in the area.

Conclusion

I would like to conclude, that both skimming well technology and MWPS are important for their respective work purposes. Skimming well are more useful to tap good quality groundwater of the lesser thickness and obtain an appreciable amount of discharge whereas MWPS has the main objective to lower down the level of the water table as in case of Faridkot area.

 

  All Skimming wells are MWPS but all MWPS are not skimming wells.