Chapter Six: Sources of Water Supply

From Ministry of Water DCOM Manual


1 Chapter Six: Sources of Water Supply

1.1 Types of Sources

Rain, snow, hail, sleet precipitate upon the surface of the earth as meteorological water and may be considered as original sources of all the water supplied to the earth. Water for drinking and other uses occurs in the form of surface water and ground water.

The following are the common sources of water for human and other activities:

  • Surface sources: a) Rivers, canals, b) streams, c) reservoirs and impoundments, d) lakes;
  • Sub surface sources: a) Infiltration wells, b) Infiltration galleries, and local springs;
  • Ground water sources: a) Open wells/protected shallow wells/boreholes.

This chapter covers the basic concepts and procedures for proper O&M of water sources and pertinent equipment used for water sources and for the preparation of water for distribution. It covers O&M of surface water (infiltration galleries, rivers, springs, etc.) and ground water (wells, boreholes, etc. and their pumps, motors and chlorinators). Three aspects should be considered in appraising water resources, e.g. water quantity, quality, and reliability.

1.1.1 Surface Water

Surface water accumulates mainly as a result of direct runoff from precipitation (rain or snow). Precipitation that does not enter the ground through infiltration or is not returned to the atmosphere by evaporation, flows over the ground surface and is classified as direct runoff water. Direct runoff is water that drains from saturated or impermeable surfaces, into stream channels, and then into natural or artificial storage sites or into the ocean in coastal areas. In addition, to serving domestic water needs, a reservoir may be used for flood control process and drought mitigation, for hydroelectric power generation, and for agricultural purposes.

The quantity of available surface water depends largely on the intensity & duration of rainfall and also varies considerably between wet and dry years. Surface water supplies may be further divided into rivers, lakes and reservoir supplies. Dams are constructed to create artificial storage. Surface water can be conveyed from canals/ open channels to the schemes through intake structures/flow regulator and transmission pipes by gravity/pumping. The style of management of lakes and reservoirs used for domestic water supplies varies widely depending on the local conditions.

The probability of contamination of surface water is very high. The factors affecting water qualities are waste water, agricultural waste, domestic and industrial discharge, grazing of livestock, and drainage from mining areas. The method of water treatment depends on the raw water quality and ranges from disinfection only to complete treatment.

1.1.2 Springs

When groundwater makes its way to the earth’s surface and emerges as small water holes or wet spots, this feature is referred to as a spring. The use of springs as the main source of community water supply is applicable whenever a spring occurs and its yield in terms of quantity and quality is sufficient. However, to maintain water quality, protection of the spring in a catchment zone has to be ensured permanently to avoid contamination. Although springs only need little operation and maintenance, monitoring of water quality has to be conducted regularly (Meuli & Wehrli, 2001).

In many rural areas, spring water is often accessed without having effected spring protection measures or having installed appropriate catchment systems. As a consequence, the spring may get contaminated and water quality may not meet the accepted and approved criteria and standards for drinking water. A properly tapped spring can improve a community’s water supply substantially if combined with adequate protection measures. If a natural spring is the source of the Utility’s water, then the area should be enclosed with a fence to prevent animals from contaminating the water and polluting the surrounding area. Different Types of Springs

The different types of springs are indicated below (Adapted from Smet & Wijk, 2002;

  • Gravity Depression Springs- occur in unconfined aquifers. Where the ground surface dips below the water table, any such depression will be filled with water,
  • Gravity Overflow Springs- A larger and less variable yield from gravity springs is obtained where an outcrop of impervious soil, such as a solid or clay fault zone, prevents the downward flow of the groundwater and forces it up to the surface,
  • Artesian Springs- artesian groundwater is prevented from rising to its free water table level by an overlaying impervious layer. It is usually under constant pressure and constantly seeks its way to the surface.

Advantages The different types of springs have the following advantages:

(a) High water quality,
(b) Fairly low construction costs where pumping is not required (gravity-based distribution system),
(c) Very little effort and cost ae needed for their operation and maintenance,
(d) High reliability of water flow and no seasonal variations (only artesian springs),
(e) O&M can be carried out by a local caretaker of the water source,

Disadvantages Despite their advantages, springs also have disadvantages including:

(a) The risk of contamination, especially for gravity springs,
(b) The need for ensured spring protection,
(c) Unstable flow, mostly dependent on rainfall (only gravity springs),
(d) Increases of water yield is not possible,
(e) Possibility of a spontaneous disappearance of the spring,
(f) Location of the spring may not be convenient or easily accessible for water to a community
(g) Opportunities for spring tapping are limited to specific regions (depending on topography, geology and hydrology). The Spring Box

To enhance the utility of a spring as a source of water for human use, as well as to protect it from erosion, it should be provided with a spring box, which is a concrete structure that serves three purposes:

(a) Protects the water source from contamination;
(b) Facilitates the collection of the water; and
(c) Enables sediments to settle at the bottom instead of being carried with the water.

Care must be taken during the construction of a spring box, to avoid or uproot surrounding trees whose roots could eventually damage the concrete spring box. The design should include a drain (or washout) pipe and a valve that will allow it to be drained easily for regular maintenance. Operation and Maintenance of Springs

According to Meuli & Wehrle (2001), spring catchments need very little effort in operation and a lot less maintenance than other water catchment systems. A simple design combined with high-quality construction for all structures in the catchment area will keep maintenance requirements to a minimum. Nevertheless, all spring catchments need periodic check-ups. To ensure water quality from these sources and to avoid operational problems at the catchment, a monthly control is vital. Minor jobs like basic repairs or monitoring activities can be planned and carried out by the operator (HELVETAS N.Y.). In case of major repairs (e.g. wet spots around the catchment, leaks at the spring chamber, etc.), the responsible service provider should be consulted. The following aspects have to be checked and ascertained during regular visits to the catchment area (HELVETAS N.Y.):

(a)At the protection zone:

(i) The fence protecting the area,
(ii) The installed diversion drainage above the catchment,
(iii) Wet spots indicating a leakage from the catchment,
(iv) Prohibition of trespassers such as human activity such as farming in the intake area.

(b) At the Spring Box/Chamber:

(i) Leakage at the chamber,
(ii) The firmness of the manhole cover,
(iii) Assured blockage at the supply line - water comes through the reserve (overflow) pipe,
(iv) The ventilation,
(v) The water quality and quantity (tested without equipment),
(vi) Size of Sedimentation in the chamber,
(vii) Yield of the spring in relation with the data of the previous years. Common Spring Box Failures and Remedies

Table 6.1 lists the common causes of failure in a spring box and its surroundings with clear suggestions for their remedies.

Table 6. 1: Common Spring Box Failures and their Remedies

Defect Remedy
1. Crack or leak. 1. Plug crack or leak with Portland cement mortar.
2. Damaged overflow and screen vents. 2. Replace damaged screen with a new one.
3. Clogging of drainage canal. 3. Clean drainage canal from all obstructions and check its slope.
4. Dilapidated fence. 4. Replace all worn-out posts and repair the fence.
5. Reduced spring discharge due to clogging 5. Clean the “eye” of the spring.

(Source: World Bank, 2012) Maintenance of Spring Boxes

The following are standard methods of maintaining spring boxes:

(a) If properly installed, thereafter spring boxes require little maintenance. It is recommended that the water quality be checked before it is put to use. Water quality should also be checked at least once a year, and more often if needed,
(b) The uphill diversion ditch should be inspected regularly in order to ensure that it is not eroded and that it is adequately diverting surface runoff away from the spring box,
(c) For hillside collection boxes, the uphill wall should be periodically inspected to ensure that it is not eroded and its structural robustness is maintained,
(d) The animals barring fence should always be kept in good repair. If animals are allowed to get close to the spring, they could contaminate the water and the spring, and consequently cause compaction of soil, leading to decreased flow rates,
(e) The cover should be checked frequently to ensure that:

  1. it is in place and watertight,
  2. water is not seeping out from the sides or from underneath the spring box, and
  3. the screening is in place on the overflow pipe. Repairing a Spring Box

When the concrete sides of the spring box show damage, the following steps should be taken:

(a) Drain the spring box. If it was originally constructed with a drain pipe and valve, drain the water and repair it. If the box does not have a drain pipe or if the leaks are below the water level of the drain pipe, you must siphon the water out. If the volume of water is too big for a water hose to siphon the water out, you will have to use a water pump,

(b) Mix an appropriate amount of water and concrete. Quick setting cement will prove helpful. Trowel the concrete onto the cracks of the damaged areas on both the inside and outside of the box. c) Attend to the spring box to keep water from damaging the newly laid concrete, which usually takes 5 to 6 hours to cure. If you had to siphon the water out, make sure that the hose does not clog or stop siphoning, or that the pump does not stop working. Removing Sediment and Disinfecting a Spring Box

Once a year, the system should be disinfected and the sediment removed from the spring box as follows:

(a) Open the valve on the outlet pipe, allowing the spring box to drain,
(b) Remove any accumulated sediment from the box and wash the interior walls with a chlorine solution. The solution for washing the spring box should be mixed at a ratio of 10 litres of water with 0.2 L chlorine bleach,Caution: Chlorine and chlorine compounds irritate the eyes and skin. Wear protective clothing and equipment such as gloves and safety glasses when dealing with or handling chlorine.
(c) After the spring box has been cleaned, 100 mg/l chlorine should be added directly to the water in the spring box, followed by a second application after 12 hours. These consecutive applications should provide for adequate disinfection. If possible, water samples should be analyzed periodically to detect any contamination and taking appropriate treatment measures.

1.1.3 Intake structures

An intake is a device or structure placed in a surface water source to permit withdrawal of water from the source and its discharge into an intake conduit through which it will flow into the water treatment works system. The types of intake structures should consist of intake towers, submerged intakes, intake pipes or conduits, movable intakes, and shore intakes. Intake structures over the inlet ends of intake conduits are necessary to protect against wave action, floods and stoppage of water flow.

Intake towers are used for large waterworks drawing water from lakes, reservoirs and rivers. Navigation, ice, pollution, and others interfere with the proper functioning of the intake tower due to either a wide fluctuation in water level or the desire to draw water at a depth to source water of the best quality and avoid clogging or for other reasons. Typical intake structures can be seen in Volume I (Appendix L) of the DCOM Manual. Problems and necessary steps in operation

Some of the problems that may arise during the operation of Intakes are given below, and therefore necessary steps should be taken to set right the same:

(a) Fluctuations in water level, water withdrawal at various depths,
(b) Hydraulic surges, ice, floods, floating debris, boats and barges,
(c) Withdrawal of water of the best available quality to avoid pollution, and to provide structural stability,
(d) Operation of racks and screens to prevent entry of objects that might damage pumps and treatment facilities,
(e) Minimising damage to aquatic life,
(f) Preservation of space for equipment cleaning, removal and repair of machinery, Storing, movement and feeding of chemicals,
(g) Screens should be regularly inspected, maintained and cleaned,
(h) Mechanical or hydraulic jet cleaning devices should be used to clean the screens,
(i) Intake structures and related facilities should be inspected, operated and tested periodically at regular intervals,
(j) Proper service and lubrication of intake facilities is important,
(k) Operation of gates and valves.

Some of the causes of faulty operation are as indicated below:

(a) Settlement or shifting of supporting structures which could cause binding of gates and valves,
(b) Worn, corroded, loose or broken parts,
(c) Lack of use,
(d) Lack of lubrication,
(e) Improper operating procedures,
(f) Vibration,
(g) Design errors or deficiencies,
(h) Failure of power source or circuit failure, and
(i) Vandalism. Safety

When working around intake structures proper safety procedure involving use of electrical and mechanical equipment and water safety should be observed. Proper safety procedures should be documented and included in the manual containing the operating procedure.

1.1.4 Dams

This section explains about the Operation and Maintenance (O&M) of dams. It provides procedures, guidance and standard forms for the normal operation and maintenance of the facilities. The Emergency Action Plan (EAP) should be utilized for unusual and emergency conditions. The purpose of the O&M Manual is to ensure adherence to approved operating procedures over long periods of time and during changes in operating personnel. The discussion presented in this volume is related to earthfill and rockfill dams which are the main concerns as stated in other volumes of the DCOM Manual. Operational Procedures

Reservoir Operations

Reservoir operating data, such as Elevation-Storage and Emergency Spillway Rating Curve, are provided and should be prepared and used during operation of the facility.

Filling Schedule Filling will begin during rainy seasons. This period, the dam owner should be aware to regulate the control gates unusual floods which may result in failure hazard. First filling of an earthfill dam is a critical event whereby dam failures can occur. Due to this fact, the dam operator should regulate the outlet structure to safeguard the embankment dam.

Release Schedule A decision is made to begin releasing water based on the rainfall, moisture conditions, and water demand. The outlet structure is inspected and cleaned of debris or sediment if present, and the gates are adjusted based on demand.

Flood Operation At the earliest possible indication of abnormally heavy rainfall or runoff in some catchment or basins, the dam attendant should station himself at the dam and open the outlet to its full capacity guided by the relevant approved operational and security protocols. If it appears likely that high outflows from the emergency spillway will occur, a warning should be given to the downstream residents to prepare for evacuation as outlined in the Emergency Action Plan.

Control Gates The control gates should be operated as per designed schedule and protocol. The release schedule should be well designed and reviewed periodically to meet the intended downstream water demand. Monitoring and Inspection


Dam Instrumentation refers to a variety of devices installed within, on, or near the dam to monitor structural behavior during construction, initial filling and subsequent operation. Instruments provide a means for detecting abnormal conditions which could lead to major problems.

This section describes the instrumentation at a Dam, the methods and frequency of data collection, transmittal of data, and procedures to evaluate the data. Timely evaluation of instrumentation readings is critical if an abnormal condition is to be detected to allow for effective corrective action. The Dam operator is primarily responsible for collecting and reporting instrumentation readings. Periodic owner inspections should be performed by the Dam operator. Inspection of a Dam and appurtenances will be scheduled and followed:

  • Schedule depending on the complexity of the project (may be monthly or seasonally),
  • Yearly for routine operation and maintenance inspections,
  • Periodically (not to exceed five years) for comprehensive inspections and engineering reviews,
  • After critical events including severe rain or wind storms, earthquakes, or periods of extremely high storage.

Monitoring Piezometers The piezometers are used to monitor the pore pressure of the dam foundation. guide for reading taking and measuring should be well defined and the dam attendant should take readings regularly as per design.

Drains and Seepage

  • Remove debris in and around the weirs to prevent clogging,
  • Remove debris and repair the small drainage channels leading to the weirs so that water is properly directed and contained within the channels,
  • Clean algae and dirt from the weir staff gauges to allow easy reading,
  • Keep the weirs level to assure accurate readings.

Yearly Inspections As the dam owner, should assign personnel to conduct the annual operation and maintenance inspections. Inspections of the embankment should occur when the reservoir is full, while inspections of the outlet works should occur while it is empty. The dam owner should prepare a checklist to be deployed during inspection of the dam and appurtenances

Periodic Owner Inspections An informal Owner Inspection should be performed twice yearly (at the beginning and end of the rain seasons). The inspection should include a systematic review of the conditions at each dam including the outlet works including the spillway. Digital photographic records of project features should be included with the inspection files. The checklist should be prepared by the dam owner.

Periodic Engineer Inspections Inspections by a qualified engineer should also be performed if unusual conditions occur or after critical events, such as earthquakes or extremely high reservoir storage levels. This is termed as Comprehensive Facility Review (as per Water Resources Management Dam Safety Regulations Gazetted through Government Notice 237 of 2013). The Dam operator should follow the guideline provided by the Ministry of Water in conducting the Comprehensive Facility Review (CFR) of the dam and its appurtenances.

Critical Event Inspections The dam should be inspected during or immediately following the occurrence of critical events, such as severe rain or wind, earthquakes or periods of extremely high reservoir elevation. If emergency conditions are observed, the responses outlined in the Emergency Action Plan (EAP) should be implemented. Emergency conditions include erosion threatening the integrity of the dam, seepage that is cloudy or excessive and/or extremely high water surfaces. Inspection by a qualified engineer should be performed to evaluate the impact of critical events on the dam. Spillway erosion seems to be a common feature in most dams constructed in rural areas in Tanzania.

Even if the water surface level is not at a high elevation at the time of an earthquake, it is possible that the dam could suffer some ill-effects from the earthquake (associated with seepage performance) that will not show up until higher reservoir elevations are subsequently reached. Therefore, heightened awareness and possible monitoring would be appropriate following an earthquake whenever the reservoir is rising to elevations that have not been previously experienced since the occurrence of the earthquake. Specific changes to monitoring schedules would need to be established on a case-by-case basis in light of the magnitude of the earthquake, reservoir elevation at the time of the earthquake, and apparent damage sustained by the dam as a result of the earthquake. Maintenance

Critical Conditions

The following conditions are critical and require immediate repairs or maintenance under the direction of a qualified engineer. The critical repairs or maintenance needs to address the specific conditions encountered and are not covered in this O&M Manual. Critical conditions should trigger a response as outlined in the Emergency Action Plan.

  • Erosion, slope failure or other conditions which are endangering the integrity of the dam,
  • Piping or internal erosion as evidenced by increasingly cloudy seepage or other symptoms,
  • Spillway erosion, blockage or restriction,
  • Excessive or rapidly increasing seepage appearing anywhere near the dam site.

Periodic Maintenance

The following items should be noted in the operations log and added to the work schedule whenever they are noted during Operational Inspections or Periodic Inspections. The following maintenance items should be completed as soon as possible after identification (at least annually):

  • Remove bushes and trees from the embankment and abutments,
  • Repair erosion gullies,
  • Repair defective gates or valves,
  • Repair deteriorated concrete or metal components,
  • Maintain riprap or other erosion protection.

Continued maintenance should also be performed for the following items:

  • Test, clean and lubricate gates and valves,
  • Inspect and maintain instrumentation and gauging equipment,
  • Remove debris from the dam area and emergency spillway approach and exit channel,
  • Remove debris from embankment face and from areas around the intake structures,
  • Clean and remove debris from seepage weirs and small drainage ditches.

Embankment Maintenance

(a) Fill erosion gullies with properly compacted cohesive soil material. Seed or riprap repaired area to stabilize from future erosion,
(b) Fill rodent burrows with slurry of soil, cement and water. Remove the rodents,
(c) Maintain grass cover by spraying weed killers, fertilizing and watering as needed,
(d) Remove brush, bushes and trees from embankment and refill with compacted soil,
(e) Add or repair riprap where displacement or other damage occurs,
(f) Maintain grading of the embankment crests to prevent potholes, rutting or other potential for standing water to accumulate,
(g) Maintain fences to provide site security and to exclude livestock from the embankments,
(h) Repair and re-vegetate damaged embankment surfaces,
(i) Perform regular inspections of the embankments and abutments to identify potential maintenance items.

Outlet Maintenance

(a) Test gates and valves semi-annually,
(b) Lubricate gates and valves annually or as recommended by the manufacturer,
(c) Repair defective gates and valves to ensure smooth operation and prevent leakage,
(d) Repair deteriorated concrete or metalwork,
(e) Remove debris from the outlet channels annually, inspect and repair erosion protection,
(f) Repair and verify calibration of water measurement equipment.

1.2 Groundwater

The groundwater sources are used as follows:

(a) Dug well / protected shallow well,
(b) Borehole.

1.2.1 Operation and Maintenance Activities for a Dug Well/Protected Shallow Well

Good O&M seeks to avert well failures, which are usually indicated by reduced (if not complete loss of) pump discharge, or deterioration in the quality of the water. Good O&M actually begins even before a well is put into operation. Before actually operating a well, the utility must determine/obtain the following information which will guide its well operating and O&M procedures:

(a) Safe pumping level,
(b) Pump curves,
(c) Well design,
(d) Location of discharge line shut-off valve and pressure gauge.
(e) Specific capacity: is a quantity that which a water well can produce per unit of drawdown. It is normally obtained from a stepped drawdown test. The specific capacity of a well is also a function of the pumping rate it is determined at. Due to non-linear well losses the specific capacity will decrease with higher pumping rates. This complication makes the absolute value of specific capacity of little use; though it is useful for comparing the efficiency of the same well through time (e.g., to see if the well requires rehabilitation). Operation and Maintenance Resources for a Dug Well

Unskilled labour is required for daily tasks and for collecting user charges. Semi-skilled labour (Well Operator) is needed to carry out weekly and monthly O&M tasks; a private fitter or plumber may be needed to repair the well pulley. Skilled labour (mason) is needed to work with the caretaker on yearly O&M tasks and to repair the concrete apron and support posts for the pulley.

Materials and equipment include the bucket and rope, fencing, support posts, brush, digging and hand tools, cement, pulley and pulley shaft and bearings, and masonry tools to be provided to the operators. Operation and Maintenance of a Dug Well

Daily, monthly and annual activities should include the following O&M activities for dug wells:

(a)Daily Activities

  1. Check for any debris in the well by regular visual inspection and remove it,
  2. Clean the concrete apron,
  3. Clear the drains,
  4. Check that the gate is closed,
  5. Check the condition of the rope, pulley, bucket and fence by regular visual inspection and replace when needed,
  6. Observed problems to be reported to the CBWSOs,
  7. Disinfection.

(b) Monthly/Quarterly activities

  1. Replace the bucket and other parts as needed,
  2. Check the concrete apron and well seal for cracks and repair them with cement mortar as needed,
  3. Record the water level with a rope-scale and report to the CBWSO leadership or superiors,
  4. Lubricate the components with grease periodically,
  5. Verify any structural damage and repair it as per need,
  6. De-silting of dug wells periodically as required, especially during rainy season.

(c) Annual activities

  1. Dewater the well and clean the bottom,
  2. Inspect the well walls and lining, and repair as needed,
  3. Check the water level and deepen the well as needed,
  4. Check the support posts for the pulley and repair as needed.

1.2.2 Mechanized Boreholes Boreholes and Dug Wells with Pump Sets

A borehole is a type of water well in which a long 100–350 mm diameter stainless steel tube or pipe is bored into an underground aquifer. The depth of the wells depends on the depth of the water level in the aquifer.

Boreholes may be fully cased and screened in overburden/alluvium strata and the top of the borehole shall be sealed to prevent pollution through percolation of water into the borehole. After installation of the bore, the top of the borehole at the riser pipe shall be caped to prevent contamination of the borehole by surface water and debris etc. An isolation valve and non-return valve are fitted on a horizontal section of the delivery pipe, adjacent to the bore well to prevent the backflow. Typically, the pump house or fabricated panel box is located next to the borehole and is housed with the control panel for operation of the electric pump. Motor service frequency in terms of running hours shall be usually specified as per catalogue and indicated to the operator. The manufacturer’s O&M manuals should essentially be followed. Appendix 1 illustrates the maintenance of different types of boreholes. Operation and Maintenance of a Borehole

(a) Daily:

  • Operate pump starter and isolation valve,
  • Check reading on ammeter is normal – stop pump if electric motor is drawing too much current,
  • Verify whether adequate water is being delivered,
  • Continue to check voltmeter and ammeter readings during the day.

(b) Monthly/Quarterly:

  • Clean the pump house,
  • Check for leaks in the rising main,
  • Testing water quality using a Field Test Kit.

(c) Annually:

  • Remove the pump and rising main from the well and inspect,
  • Check pipe threads and re-cut corroded or damaged threads,
  • Replace badly corroded pipes,
  • Inspect electric cables and check insulation between cables,
  • Record servicing and maintenance in log book,
  • De-silt borehole if required,
  • Check screen and clear as needed.

Appendix 2 illustrates the troubleshooting for boreholes problems. Preventive Maintenance/Pumping Tests results

According to available data, the specific yield of wells should be measured annually and compared with the original specific yield by the hydrogeologist/driller and the record of the same shall be maintained. As soon as 10 to 15% decrease in specific yield is observed, steps should be taken to determine the cause and corrective measures should be taken accordingly. Rehabilitation procedures should be initiated before the specific yield has declined by 25%. A checklist given below can be used to evaluate the performance of a well:

(a) Static water level in the production well,
(b) Pumping rate after a specific period of continuous pumping,
(c) Specific yield after a specified period of continuous pumping,
(d) Sand content in a water sample after a specified period of continuous pumping
(e) Total depth of the well,
(f) Efficiency of the well. The efficiency of a pumping well is expressed as the ratio of aquifer loss (theoretical drawdown) to total (measured) drawdown in the well. A well efficiency of 70% or more is usually considered acceptable while a value of 65% is being accepted as the minimum efficiency (Kresic, 1997). A perfectly efficient well, with perfect well screen and where the water flows inside the well in a frictionless manner would have 100% efficiency,
(g) Normal pumping rate and hours per day of operation,
(h) General trend in water levels in wells in the area,
(i) Draw down created in the production well because of pumping of nearby wells.

A significant change in any of the first seven conditions listed above indicates that a well or pumping rate is required. For, preventive maintenance programme well construction records showing geological condition, water quality and pumping performance shall be collected. The data of optimum and efficient limit of operation should be available which is created at the time of testing and commissioning of the well. This data is normally in the form of a discharge draw-down curve (called yield draw down curve). The pumping water level and draw down can be measured with the help of an electric depth gauge of an airline gauge. Pumping tests

Pumping tests are carried out to determine the safe pumping yield, which establishes how much groundwater can be taken from a well, and what effects pumping will have on the aquifer and neighboring well supplies. It is one of the design parameters for selecting the pump to be used.

The pumping tests are usually done by well drilling contractors who are knowledgeable and who possess the required tools and equipment for the tests. It is rare for a utility/WSSAs/RUWASA to conduct this test itself. However, should this become necessary, the general procedure for conducting such a test as illustrated in Appendix 3 shall apply. Once the safe pumping level is established, it should be compared with the design pump curves of the equipment to be used. This will guide the operational parameters for pumping water from the well. Causes of Failure of Wells

Well may fail due to inadequate design, faulty construction and operation, lack of timely maintenance. The main causes for source failure are categorized as under:

(a) Incorrect design: for instance use of incorrect size of screen and gravel pack, wrong pin pointing of well site resulting in interference;
(b) Poor construction e.g. the bore may not be vertical; the joints may be leaky, wrong placement of well screen, non-uniform slots of screen, improper construction of cement slurry seal to prevent inflow from Saline aquifer;
(c) Corrosion of screens due to chemical action of water resulting in rupture of screens;
(d) Faulty operation e.g. over pumping, may causes the rupture of strainer casing pipes due to piping action of water, poor maintenance;
(e) Adverse aquifer conditions resulting in lowering of the water table and deterioration of water quality;
(f) Mechanical failure, e.g. falling of foreign objects including the pumping assembly and its components;
(g) Encrustations due to chemical action of water;
(h) Inadequate development of wells;
(i) Placement of pump sets just opposite the strainer casing pipes, causing entry of silt by rupturing slots of pipes. Monitoring of Silt Coming out with Water During Pumping from Source

Indication for silting

(a) Appearance of fine silt with water is an early indication of silting,
(b) Reduction in depth of borehole/ open well,
(c) Reduction in yield of borehole.v

Causes for silting

(a) Over pumping,
(b) Improper sitting of casing pipe,
(c) Improper jointing of casing pipes,
(d) Placement of pump sets just opposite the strainer casing pipe,
(e) Poor development of bore wells.

Suggestions to overcome silting

(a) Periodical inspection of a borehole,
(b) Additional length of casing pipe may be inserted in the case of improper borehole assembly installation,
(c) Flushing of borehole,
(d) Re-development of borehole,
(e) Replacement of pump sets with proper duty condition, with respect to the safe yield of the borehole. Rejuvenation of Boreholes

A decision whether to rejuvenate an old well or construct a new one based on the cost benefit analysis. The following remedial measures can be taken for correcting the situation as mentioned in Section (preventive maintenance).

1.2.3 Faulty Operation

Borehole should run in such a way that the pumping water level should always remain above the level of well screen. Over-pumping will expose the well screen, which may result in encrustation and corrosion. Over pumping results in excessive draw down which may cause differential hydrostatic pressures, leading to rupture of well screen. Negligence in timely repair and maintenance may result in poor performance of the tube well. Therefore, before any permanent damage is done to tube well it should be ensured that the tube well is operated at its designed capacity and timely repair and maintenance are done. Adverse Aquifer Conditions

In adverse aquifer conditions where water table has depleted but the quality has not deteriorated, wells can generally be pumped with considerably reduced discharge. Mechanical Failure

The falling of pumping set assembly and its components into the borehole can be minimized by providing steel wire holdings throughout the assembly length including pumping set or by providing and clamping a steel strip around the pumping assembly. However, in spite of proper care, sometimes foreign objects and pumping set assembly components may fall in the well. In corrosive water the column pipe joints and pump parts may get progressively weakened due to corrosion, get disconnected and fall into the well. However where well screen is not damaged, then by proper fishing the fallen objects can be taken out of the well making it functional again. Following are the one of the method taken for fishing out the fallen objects in the boreholes:

(a) Impression Block: An impression block is used to obtain an impression of the top of the object before attempting any fishing operation. Impression blocks are of many forms and design. An impression block made from a block of softwood turned on a lathe. The diameter of the block is 2 cm less than that of drilled hole. The upper portion is shaped in the form of a pin and driven to fit tightly into the box collar of a drill pipe. To ensure further safety, the wooden block is tied with wire or pinned securely to the collar. Alternatively, the block could be fixed to a bailer. A number of nails are driven to the lower end of the block with about 1 cm to projecting out. A sheet metal cylinder of about 5 to 7 cm is temporarily nailed around the block to hold molten wax, which is poured into it. Warm paraffin wax, soap or other plastic material poured into the cylinder is left to cool and solidify. The metal cylinder is then removed; the nail heads hold the plastic material to the block. To locate the position of a lost object, the impression block is carefully lowered into the hole until the object is reached. After a proper stamp is ensured, the tool is raised to the ground surface, where the impression made in the plastic material is examined for identifying the position of the lost object and designing or selecting the right fishing tool.

(b) Fishing Tools to Recover Fallen Objects: The term ‘fish ‘describes a well drilling tool, pump component or other foreign body accidentally fallen or struck in bore wells. The type and design of fishing tools required for a specific job, depends on the positioning at which it is lying in the well and the type of object to be lifted/ fished. However, series of fishing tools suitable for different jobs are available in the market, which could be adapted or modified to suit a particular requirement. The following are some of the methods of fishing process:

(i) External catch Fishing tools that engage the fish on its outer diameter. These tools help to recover equipment down hole by using a grapple or by threading directly to its outside surface.

(ii) Internal catch Fishing tools that engage the fish in its inner diameter. Similar to external catch tools, this is achieved by a grapple or by threading directly to the fish’s inside surface. Gripping and Releasing Mechanism

The bowl of the overshot is designed with helically tapered spiral section on its inside diameter. The gripping member (Spiral grapple or basket grapple) is fitted in to this section. When an upward pull is exerted against a fish, an expansion strain is spread evenly over a long section of the bowl and the compression strain is spread evenly over a long section of the fish. No damage or distortion occurs to either the fish or the overshot. This design permits a far stronger tool with a smaller outside diameter than is possible with an overshot that employs a single tapered section which supports slips.

A spiral grapple is formed as a left hand helix with a tapered exterior to conform to the helically tapered section in the bowl. Its interior is whickered for engagement with the fish.

A Basket grapple is an expandable cylinder with a tapered exterior to conform to the helically tapered section in the Bowl, its interior is whickered for engagement with the fish. Two types of basket grapple are available to meet the need for catching various types of fish.

The basket grapple with long catch stop has an internal shoulder located at the upper end to stop the fish the best catch position. It is designed to stop and catch collars and tool joints with sufficient length left below the grapple to allow the joint to be packed off with a basket control packer.

Grapple controls are of two types Spiral grapple controls are used with spiral grapples basket controls are used with basket grapples. Grapple controls are used as a special key to allow the grapple to move up and down during operation while simultaneously transmitting full torque from the grapple to the bowl.

Spiral Grapple controls are always plain: Basket grapple controls may be either plain or include a pack off in addition to the pack off mill teeth is included. In operation, the overshot functions in the same manner, whether dressed with spiral grapple parts or basket grapple parts.

During the engaging operation, as the overshot is rotated to the right and lowered, the grapple will expand when the fish is engaged, allowing the fish to enter the grapple. Thereafter with rotation stopped and upward pull exerted, the grapple is contacted by the tapers in the bowl and its deep wickers grip the fish firmly.

During the releasing operation, a sharp downward pump places the larger portion of the bowl tapers opposite the grapple breaking the hold. Thereafter, when the overshot is rotated to the right and slowly elevated, the wickers will unscrew the grapple off the fish.

Operation Engaging and pulling the fish connect the overshot to the fishing string and run it in the hole. As the top of the fish is reached, slowly rotate the fishing string to the right and gradually lower the overshot over the fish. Allow the right hand torque to stock out of the fishing string and pull on the fish by elevating the fishing string. If the fish does not come, start the circulating pumps and maintain a heavy upward strain while fluid is forced through the fish. Releasing from the Fish

Drop the weight of the fishing string heavily against the over shot, then simultaneously rotate to the right and slowly elevates the fishing string until the overshot is clear of the fish. To release from a recovered fish, follow the same procedure while holding fish below the overshot. Rotary Taper Taps

Rotary taper taps are simple, rugged, dependable internal catch fishing tools.

Operation: Run the taper tap in the hole to the top of the stuck fish. Apply less than one point of weight; rotate the tap until the tapered threads have engaged the fish. Stop rotation and pull the fish from the hole.

Rotary taper, Taps are furnished in two types: Plain or skirt type, plain taper taps do not have a skirt thread provided on the shoulder. Skin type tapers taps are threaded for a skirt. A skirt is used when the hole size is drastically different from the fish size. The taper tap can be dressed with a skirt or a skirt and oversize guide. This will allow for the taper tap to be guided into the fish more easily during the fishing operation. Re-Development of Boreholes

Sometimes due to carelessness at the time of construction, proper development of the boreholes is not done which results in constant inflow of the sand particles causing choking of the filtering media and strainers. Such boreholes need re-development. The re-development of borehole will have following effects:

(a) Re-development of well involves removal of finer material from around the well screen, thereby enlarging the passages in the water-bearing formation to facilitate entry of water;
(b) Re-development removes clogging of the water-bearing formation;
(c) It increases the porosity and permeability of the water-bearing formation in the vicinity of the borehole;
(d) It stabilise the formations around the well screen so that the borehole will yield sand-free water;
(e) Re-development increases the effective radius of the well and, consequently, its yield. Methods of Re-development

Following are the methods of well re-development:

(a) Over-pumping with pump,
(b) Surging with surge block and bailing,
(c) Surging and pumping with air compressor,
(d) Back-washing,
(e) High-velocity jetting,
(f) Dynamiting and acid treatment
. For rehabilitation purpose any suitable method of re-development can be used as mentioned above. The largely used method is surging and pumping with compressed air. Operation and Maintenance Staff Activities of Mechanized Boreholes

(a) Daily O&M activities:

  1. Clean the pump house,
  2. Check available Voltage in every phase,
  3. Check reading on ammeter is normal – stop pump if electric motor is drawing too much current and report problems, open isolation valve,
  4. Check power factor,
  5. Confirm water is being delivered,
  6. Check for leaks in the rising main,
  7. Continue to check voltmeter and ammeter readings during the day,
  8. Maintain pumping log book and history sheets of tools, plants & equipment’s,
  9. Observe the abnormal sound of pumping machinery by listening the changes in noise level.

(b) Weekly activities at the tank: Testing water quality using a Field Test Kit (for small schemes only).

(c) Monthly activities: Billing and collection, and deposit with the water authorities/water committees (for small schemes only).

(d) Annual activities may include:

(i) Remove the pump and rising main from the well and inspect,
(ii) Check pipe threads and re-cut corroded or damaged threads,
(iii) Replace badly corroded pipes,
(iv) Inspect electric cables and check insulation between cables,
(v) Check as per recommendations of manufacturer’s operational manual. Operation and Maintenance Resources for Mechanized Boreholes

Semi-skilled labour (pump operator) is required for pump operation, billing and collection. Skilled labour is required for pump and motor servicing and maintenance. Materials and equipment include pipes for the rising main, tools for maintenance and repair, oil for the motor, spare parts for the motor and electrical control panel. Finances would typically be from the household paying water charges, or CBWSOs resources and Government funds.

1.2.4 Artificial Re-Charging of Under Ground Source

The yield in the source can be improved by artificial recharging structures. Artificial recharge of ground water can be achieved by the following:

(a) Stream flow harvesting comprising of:

  • Gully plugging /small boulder dams,
  • Loose stone check dams (LSCD),
  • Dams.

(b) Surface flow harvesting:

  • Tank,
  • Ponds.

(c) Direct recharge

  • Recharge of wells,
  • Through injected wells,
  • Through roof top rainwater harvesting structures.

Note: The O&M of such structures may be done as per the sustainability practices and manuals.

1.2.5 Infiltration Wells and Their Maintenance

Infiltration well is located in river beds where sufficient sand depth is available. These wells are sunk up to the depth where hard strata are met with. The porous concrete portion will facilitates infiltration of water in to the well. The diameter generally varies from 3 m to 5 m. The regular inspection of infiltration well needs to be conducted.

If illegal sand mining is done around or near the well, there is the possibility of the structure getting tilted to one side. To obviate this problem, it is essential to protect the infiltration well from sand mining. Sometimes the wells may get tilted due to sand erosion during flood times and to overcome this problem packing of sand bags around the wells should be done. It should be ensured that flood water does not enter into the well through the manhole cover during flood times and hence the manhole cover must be made water tight. Water quality test and specific yield of the well should be conducted during pre- rainy season and post rainy season period to assess the quality of water and the yields.

1.2.6 Infiltration Gallery

An infiltration gallery is a horizontal well which is used to collect naturally filtered water. It consists of a main collection sump and perforated pipe water collectors, which are surrounded by a blanket of sand and gravel (Appendix 4). The pipe should be driven into the well with proper slope to ensure continuous flow and the well points (horizontal drain) should be well under water table in dry season. Infiltration galleries need soils which are permeable to allow sufficient sub-surface water to be collected. The gallery should be surrounded with a gravel pack to improve flow towards it and to filter any large particles that might block the perforation.

Infiltration gallery is often used in conjunction with other water supply scheme as a means of increasing the quantity of water intake in areas of poor water yield in this instance one or more galleries are built which drain into the central point, such as a hand dug well or spring box. These are called collector wells, it is important to protect it from contamination by locating it uphill and the minimum safe distance from any source of contamination. Operation of Infiltration Gallery

Water enters the perforated pipe collectors and then flows by gravity to the main collection sump or well. From this sump or well, water is pumped out to the distribution system. Maintenance of Infiltration Gallery

The following O&M aspect shall be followed:

(a) Never exceed the design pumping rate- not more than 60% of the yield. Higher pumping rate could cause fine sediment to enter the filter and reduce the opening size of slots and the sand may enter screen and block the part of intake opening causing more sand pumping,

(b) Do not let the gallery unused for longer time since it may tend to lower the hydraulic conductivity of filter pack,

(c) The maintenance of galleries involves back washing and chemical treatment. The back washing time required can be 5-10 minutes. For back washing, compressed air can also be used. Sanitary inspection of Infiltration Gallery

Sanitary inspection of infiltration Gallery is required to be conducted in once a year by water supply agency, particular attention should be paid to the catchment area of the gallery, especially with shallow galleries. The water collected in infiltration galleries has often not had as much filtration as well or spring water thus may be more vulnerable to contamination. Water quality testing should be done twice a year, once in the wet season and once in the dry season. The water at various points in the gallery, at the collector well or sump and the distribution system should also be tested. Common Causes and Corrective Measures for Infiltration Gallery Failure

(a) Clogging of the Filter Bed – The clogging of the filter blanket surrounding the collector pipes is indicated by the lowering of the water level in the main sump/well while pumping at the normal rate. This clogging is due to the deposition of fine silt on the filter blanket. The clogging material usually can be dislodged by surging, using compressed air or a force pump. If these methods will not work, the only remedy is to dig up and clean the sand/gravel blanket.

(b) Poor Quality of Water Yield – The most probable cause of the deterioration in water quality is a defective filter bed, which allows contaminants to pass through. The water yield may be rendered safe again either by repairing the filter bed or by continuous chlorination.

1.2.7 Groundwater management

Groundwater and surface water are closely linked such that all water should be managed as one resource. Managing groundwater resources is primarily aiming at sustainable development of the resource for various users. A key issue of sustainable groundwater is balancing the available resources with the increasing demands of water use. It should be noted that water is an economic as well as social good. To that end, the following resources management objectives are crucial:

  • Balancing groundwater recharge against abstraction is the main emphasis of groundwater management.
  • Groundwater protection from pollution.

For effective groundwater management, stakeholder’s involvement is very important.

Groundwater management studies are conducted in following levels:

  • Preliminary examination- based largely on judgement by experienced personnel.
  • Reconnaissance- this study considers possible alternatives in the formation of a water management plan to meet a defined need for an area, including estimates of benefits and costs.
  • Feasibility- This study requires detailed engineering, hydrogeologic, and economic analyses together with cost and benefit estimates to ensure that the selected project is an optimum development.
  • Define project- this involves planning studies necessary for defining specific features of the selected project.

In conducting groundwater basin investigations, the following data are needed:

  • Topographic (contour maps, aerial photographs, benchmarks)
  • Geologic (surface and subsurface)
  • Hydrologic (surface inflow and outflow, precipitation, changes in surface storage, changes in soil moisture, change in groundwater storage)

A suite of observation wells coupled with a selection of abstraction wells normally comprise a monitoring network, which should be designed so as to provide the required access to the groundwater resource. Monitoring networks and systems are classified into three main (but not mutually exclusive) groups, and are specifically designed and operated to:

  • detect general changes in groundwater flow and trends in groundwater quality, and bridge gaps in scientific understanding of the groundwater resource base (Primary Systems)
  • assess and control the impact of specific risks to groundwater (Secondary and Tertiary Systems).

Table 6. 2: Types of Data Required for Groundwater Management

Type of Data Baseline Data
(From Archives)
Baseline Data
(From Field Stations)
Groundwater Occurrence and aquifer properties •Water well records (hydrogeological, logs, instantaneous groundwater levels and quality),
•Well and aquifer pumping tests.
•Groundwater level monitoring,
•Groundwater quality monitoring.
Groundwater use •Water well pump installations,
•Water-use inventories,
•Population registers and forecasts,
•Energy consumption for irrigation.
•Water well abstraction monitoring (direct or indirect),
•Well groundwater level variations.
Supporting Information •Climatic data,
•Land-use inventories,
•Geological maps/sections.
• Riverflow gauging,
•Meteorological observations,
•Satellite land-use surveys,

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