Intakes

A spring intake (spring box or spring capture) is a small chamber built at the spring eye to collect all the flow from the spring, protect it from pollution, and send it to the pipeline by gravity. It is the most common intake for rural hilly areas of Nepal because springs give clean water at a high level.

Parts of a spring intake

• Collection chamber (spring box) of stone masonry or concrete, with a pre-cast cover and manhole.
• Gravel filter / perforated pipes at the back wall to collect water uniformly from the spring eye.
• Outlet pipe with a gate valve (and a strainer) to the pipeline.
• Overflow pipe to take excess water; washout (drain) pipe with a valve for cleaning; vent pipe with a screen.
• Protection works: clay/impervious cap over the spring, a diversion drain (catch drain) uphill to divert surface water, a fence, and a vegetation or plantation cover.

Plan

   Diversion drain (uphill)
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  |    fence                    |
  |   +---------------------+   |
  |   | gravel filter ::::  |   |
  |   |  (spring eye)       |-->| overflow
  |   | collection chamber  |   |
  |   |  [manhole]   outlet |==>| pipe to tank
  |   +----------+----------+   |
  |         washout pipe        |
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Section / elevation

        Vent      Manhole cover
         |   ____|_____
  ground |  |          |  clay cap (0.5 m)
  =======+--+          +=============
         |  |  air     |
 Spring->|::| water lvl|--> overflow
 gravel  |::|~~~~~~~~~~|
 filter  |::|          |==> outlet+valve
         |__|__________|
              washout pipe

General river intake

A river intake is a tower or well built in (or at the edge of) the river with openings at different levels. Water enters the openings through screens, passes into the well and then flows by gravity (or is pumped) through the intake pipe to the treatment plant.

   Foot bridge
  =========|===========
           |   Intake tower
 HFL ~~~~~ |  [ ]  gate/valve
           | __|__ upper port
 NWL ~~~~~ |/  |  \  <-- screens
           |   |__ middle port
 LWL ~~~~~ |   |
           |___|__ lower port
  River bed ///|\\\
              \|/ intake pipe to
                   pump well/treatment

Working

• Ports at two or three levels let the operator draw the clearest water at any river stage: top ports in the low-silt season, lower ports when the river is shallow.
• Coarse and fine screens at the ports stop floating matter, leaves, fish and debris.
• Gates or valves on each port regulate flow and isolate a port for repair.
• The water travels from the intake well through the intake pipe to the pump well or the plant.
• The entrance velocity is kept low (0.15 to 0.3 m/s) so that little silt and debris is drawn in. A foot bridge gives access for operation and cleaning.

Points to consider in site selection

1. Water quantity: the source must give the design flow even in the driest season; the minimum flow must exceed the demand.
2. Water quality: the site should be upstream of towns, sewage and industrial discharges, and away from tributaries that bring silt or pollution.
3. Stable bank and bed: choose a stable, non-eroding reach, preferably on the concave (outer) side of a bend where the water is deep and the current scours silt away.
4. Depth of water: enough depth at all stages so the intake port stays submerged at low water.
5. Flood level: the structure must stand above the highest flood level (HFL) or be safe against it, and the site should be free from flood and drift damage.
6. Foundation: sound strata for the foundation of the intake tower and pipes.
7. Navigation: the site must not obstruct navigation and should not be in a navigation channel.
8. Distance and elevation: close to the treatment plant and consumers (shorter pipeline, lower cost); for gravity schemes, enough head.
9. Accessibility: access for construction, inspection and maintenance in all seasons, and nearness to power for pumping.
10. Future expansion and ownership of land/legal rights at the site.
11. Ice and silt: the site should not be affected by ice formation or heavy sedimentation.

Definition

An intake is a structure built in or near a water source (river, lake, reservoir, canal or spring) to draw water safely in the required quantity and send it to the conveying main, pump well or treatment plant.

Components of an intake

1. Intake opening / port with a bell-mouth entry, placed at one or more levels.
2. Coarse screen (trash rack) with bars 20 to 50 mm apart to stop large floating objects, and a fine screen (6 to 12 mm mesh) to stop small debris.
3. Intake well / tower / chamber that houses the gates and valves and lets water settle.
4. Sluice gates / valves to regulate or cut off flow.
5. Conveying (intake) pipe or conduit from the well to the pump house or main.
6. Sump or pump well (for pumped schemes) and a foot bridge for access.
7. Protection works: pitching, groynes, wing walls, embankment, guard rails, and a flushing / scour pipe for removing silt.

General river intake

A river intake is a tower or well built in (or at the edge of) the river with openings at different levels. Water enters the openings through screens, passes into the well and then flows by gravity (or is pumped) through the intake pipe to the treatment plant.

   Foot bridge
  =========|===========
           |   Intake tower
 HFL ~~~~~ |  [ ]  gate/valve
           | __|__ upper port
 NWL ~~~~~ |/  |  \  <-- screens
           |   |__ middle port
 LWL ~~~~~ |   |
           |___|__ lower port
  River bed ///|\\\
              \|/ intake pipe to
                   pump well/treatment

Working

• Ports at two or three levels let the operator draw the clearest water at any river stage: top ports in the low-silt season, lower ports when the river is shallow.
• Coarse and fine screens at the ports stop floating matter, leaves, fish and debris.
• Gates or valves on each port regulate flow and isolate a port for repair.
• The water travels from the intake well through the intake pipe to the pump well or the plant.
• The entrance velocity is kept low (0.15 to 0.3 m/s) so that little silt and debris is drawn in. A foot bridge gives access for operation and cleaning.

Need for an intake structure

Water cannot be taken directly from a river, lake or reservoir in a safe, controlled way. The intake is needed to:

• draw the design quantity in all seasons and draw it from the best level;
• keep out floating matter, silt, fish and debris with screens;
• protect the supply from floods, scour and erosion;
• allow valves to control and isolate the flow;
• provide a stable base for pipes and pumps.

Dry type river intake

A dry intake is a tower built on the river bank (or just inside it) whose interior is kept dry. Water enters through ports in the wall, flows into a separate sump by a connecting pipe, and only the valves and pipes are in the dry chamber. The operator can work inside it at any time.

 Foot bridge ===+
                | operating floor
 HFL ~~~~~~~~~ ||   gate valves
              ||[=]---+
 NWL ~~~~~~~~ ||[=]---+--> pipe to
              ||[=]---+    sump/pump well
 LWL ~~~~~~~ ||  dry chamber
   ///////// ||____________ screens at ports
   river bed  |   (water-tight walls)

Operation

• Water flows from the river through the screened ports, then through the valves in the dry chamber, to the sump or directly to the pump.
• The operator selects the port at the best level and closes the others.
• Valves and screens can be inspected, cleaned or repaired from inside without wetting the operator.

Merits and demerits: Easy operation and maintenance, but it needs a stronger water-tight wall, deeper foundation, and is costlier than a wet intake.

When a reservoir intake is constructed

A reservoir intake is built when the supply comes from an impounding (storage) reservoir or lake, for example when the river flow in the dry season is less than the demand, so water is stored behind a dam and drawn through a tower. It is used when the quality changes with depth and season, and when the supply must be taken at a controlled level.

Typical wet reservoir intake

A reservoir intake draws water from an impounding reservoir (a lake or a lake formed by a dam). A wet intake tower is a vertical tower, usually of masonry or concrete, set in the reservoir near the dam, with ports at different depths. The water level inside the tower is the same as the reservoir.

  Foot bridge ==============+
                            | operating
  HFL ~~~~~~~~~~~~~~~~~~    | stem
  NWL ~~~~~~~[ ]~~~~~~~~~~~ |
       top port + screen    |
  MDDL ~~~~~[ ]~~~~~~~~~~~~
       middle port + screen |
       ~~~~~[ ]~~~~~~~~~~~~ |
       bottom port          |
  bed //////|  intake well  |////
            +--------pipe/conduit--> outlet to plant

Characteristics and working

• The tower has ports (usually 3) at different levels. Water is taken from the level of best quality: top water in summer when the deeper water is cold and poor (low oxygen, high iron and manganese), and deeper water in winter when the surface is cold or frozen.
• Water entering the port passes through coarse and fine screens, then the sluice gate or valve, into the well, and from the well by the intake pipe or conduit to the plant.
• Gates are operated from the top by stems and handwheels on the service platform; access is through a foot bridge.
• Low entrance velocity avoids drawing silt and floating matter. The bottom port is placed above the sludge/silt level.

Components of an intake

1. Intake opening / port with a bell-mouth entry, placed at one or more levels.
2. Coarse screen (trash rack) with bars 20 to 50 mm apart to stop large floating objects, and a fine screen (6 to 12 mm mesh) to stop small debris.
3. Intake well / tower / chamber that houses the gates and valves and lets water settle.
4. Sluice gates / valves to regulate or cut off flow.
5. Conveying (intake) pipe or conduit from the well to the pump house or main.
6. Sump or pump well (for pumped schemes) and a foot bridge for access.
7. Protection works: pitching, groynes, wing walls, embankment, guard rails, and a flushing / scour pipe for removing silt.

Wet reservoir intake for an earth dam

In an earth dam the intake is not placed inside the embankment (which would cause leakage and settlement). Instead a wet intake tower is built in the reservoir upstream of the dam, near the upstream toe, connected to the crest by a foot bridge, and the outlet conduit (a pipe in a trench, or a tunnel through the abutment or under the base) passes under or beside the dam.

  Foot bridge =======+     Earth dam
 HFL ~~~~~~~~~~~~~~~ |   /\
 NWL ~~~~~~~~~~~~[T] |  /  \
        ports --> [ ]| /    \
 bed ///////////[ ]-+------\--/////
              conduit with cut-off collars
                          ---> outlet / plant

Operation and characteristics

• Ports at different depths (top, middle, bottom) with screens and sluice gates let the operator draw the best quality water at all reservoir levels.
• Gates are lifted by stems from the service platform; the lowest port is above the silt level.
• Water flows to the well, then through the outlet conduit to the downstream valve house and plant.

Factors ensuring stability and safety of the intake works

• The tower base is founded on a firm stratum, with a foundation wide enough to resist overturning and sliding under water pressure, wave and ice loads.
• Check stability against overturning, sliding and floatation (empty well) and against the earthquake load, with the foot bridge as a hinged or sliding support.
• The conduit through the dam has cut-off collars (anti-seepage collars) to stop piping and leakage along the pipe, and is laid on firm ground, not on fill.
• Gate and valve control house is above the flood level; the tower top is above maximum water level plus wave height (freeboard).
• A flushing pipe removes silt; provide a trash rack and fine screen; and keep the conduit pressure-tested.
• Use of reinforced concrete or masonry with a water-proof cement mortar.

Factors for selecting an intake site

1. Water quantity: the source must give the design flow even in the driest season; the minimum flow must exceed the demand.
2. Water quality: the site should be upstream of towns, sewage and industrial discharges, and away from tributaries that bring silt or pollution.
3. Stable bank and bed: choose a stable, non-eroding reach, preferably on the concave (outer) side of a bend where the water is deep and the current scours silt away.
4. Depth of water: enough depth at all stages so the intake port stays submerged at low water.
5. Flood level: the structure must stand above the highest flood level (HFL) or be safe against it, and the site should be free from flood and drift damage.
6. Foundation: sound strata for the foundation of the intake tower and pipes.
7. Navigation: the site must not obstruct navigation and should not be in a navigation channel.
8. Distance and elevation: close to the treatment plant and consumers (shorter pipeline, lower cost); for gravity schemes, enough head.
9. Accessibility: access for construction, inspection and maintenance in all seasons, and nearness to power for pumping.
10. Future expansion and ownership of land/legal rights at the site.
11. Ice and silt: the site should not be affected by ice formation or heavy sedimentation.

Characteristics of a wet reservoir intake

A reservoir intake draws water from an impounding reservoir (a lake or a lake formed by a dam). A wet intake tower is a vertical tower, usually of masonry or concrete, set in the reservoir near the dam, with ports at different depths. The water level inside the tower is the same as the reservoir.

  Foot bridge ==============+
                            | operating
  HFL ~~~~~~~~~~~~~~~~~~    | stem
  NWL ~~~~~~~[ ]~~~~~~~~~~~ |
       top port + screen    |
  MDDL ~~~~~[ ]~~~~~~~~~~~~
       middle port + screen |
       ~~~~~[ ]~~~~~~~~~~~~ |
       bottom port          |
  bed //////|  intake well  |////
            +--------pipe/conduit--> outlet to plant

Characteristics and working

• The tower has ports (usually 3) at different levels. Water is taken from the level of best quality: top water in summer when the deeper water is cold and poor (low oxygen, high iron and manganese), and deeper water in winter when the surface is cold or frozen.
• Water entering the port passes through coarse and fine screens, then the sluice gate or valve, into the well, and from the well by the intake pipe or conduit to the plant.
• Gates are operated from the top by stems and handwheels on the service platform; access is through a foot bridge.
• Low entrance velocity avoids drawing silt and floating matter. The bottom port is placed above the sludge/silt level.

Type of intake and the reason

In the rural hilly area of Nepal a spring intake (spring box) is generally used, or, where there is no spring, a simple stream/side intake. The spring intake is recommended because:

• springs usually come from deep underground, so their water is clean and bacteriologically safe and needs little or no treatment;
• the spring is usually at a high level, so water flows to the village by gravity, with no pumps;
• construction is simple, uses local stone, sand and labour, and its cost and maintenance are low (suitable for community management);
• the yield is dependable through the year, and the intake keeps the water protected.

Description of a spring intake

A spring intake (spring box or spring capture) is a small chamber built at the spring eye to collect all the flow from the spring, protect it from pollution, and send it to the pipeline by gravity. It is the most common intake for rural hilly areas of Nepal because springs give clean water at a high level.

Parts of a spring intake

• Collection chamber (spring box) of stone masonry or concrete, with a pre-cast cover and manhole.
• Gravel filter / perforated pipes at the back wall to collect water uniformly from the spring eye.
• Outlet pipe with a gate valve (and a strainer) to the pipeline.
• Overflow pipe to take excess water; washout (drain) pipe with a valve for cleaning; vent pipe with a screen.
• Protection works: clay/impervious cap over the spring, a diversion drain (catch drain) uphill to divert surface water, a fence, and a vegetation or plantation cover.

Plan

   Diversion drain (uphill)
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  |    fence                    |
  |   +---------------------+   |
  |   | gravel filter ::::  |   |
  |   |  (spring eye)       |-->| overflow
  |   | collection chamber  |   |
  |   |  [manhole]   outlet |==>| pipe to tank
  |   +----------+----------+   |
  |         washout pipe        |
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Section / elevation

        Vent      Manhole cover
         |   ____|_____
  ground |  |          |  clay cap (0.5 m)
  =======+--+          +=============
         |  |  air     |
 Spring->|::| water lvl|--> overflow
 gravel  |::|~~~~~~~~~~|
 filter  |::|          |==> outlet+valve
         |__|__________|
              washout pipe

What is an intake?

An intake is a structure built in or near a water source (river, lake, reservoir, canal or spring) to draw water safely in the required quantity and send it to the conveying main, pump well or treatment plant.

Functions of an intake

• Withdraw the required quantity of water from the source throughout the year.
• Keep out floating matter, debris, fish and coarse silt by means of screens and gates.
• Draw the best quality water (away from pollution, silt and bottom deposits).
• Protect the supply from floods, scour, silting, ice and damage.
• Allow control and isolation of flow (valves, sluice gates) for repair and maintenance.

Factors affecting site selection

1. Water quantity: the source must give the design flow even in the driest season; the minimum flow must exceed the demand.
2. Water quality: the site should be upstream of towns, sewage and industrial discharges, and away from tributaries that bring silt or pollution.
3. Stable bank and bed: choose a stable, non-eroding reach, preferably on the concave (outer) side of a bend where the water is deep and the current scours silt away.
4. Depth of water: enough depth at all stages so the intake port stays submerged at low water.
5. Flood level: the structure must stand above the highest flood level (HFL) or be safe against it, and the site should be free from flood and drift damage.
6. Foundation: sound strata for the foundation of the intake tower and pipes.
7. Navigation: the site must not obstruct navigation and should not be in a navigation channel.
8. Distance and elevation: close to the treatment plant and consumers (shorter pipeline, lower cost); for gravity schemes, enough head.
9. Accessibility: access for construction, inspection and maintenance in all seasons, and nearness to power for pumping.
10. Future expansion and ownership of land/legal rights at the site.
11. Ice and silt: the site should not be affected by ice formation or heavy sedimentation.

Components of an intake

1. Intake opening / port with a bell-mouth entry, placed at one or more levels.
2. Coarse screen (trash rack) with bars 20 to 50 mm apart to stop large floating objects, and a fine screen (6 to 12 mm mesh) to stop small debris.
3. Intake well / tower / chamber that houses the gates and valves and lets water settle.
4. Sluice gates / valves to regulate or cut off flow.
5. Conveying (intake) pipe or conduit from the well to the pump house or main.
6. Sump or pump well (for pumped schemes) and a foot bridge for access.
7. Protection works: pitching, groynes, wing walls, embankment, guard rails, and a flushing / scour pipe for removing silt.

Factors governing the site selection

1. Water quantity: the source must give the design flow even in the driest season; the minimum flow must exceed the demand.
2. Water quality: the site should be upstream of towns, sewage and industrial discharges, and away from tributaries that bring silt or pollution.
3. Stable bank and bed: choose a stable, non-eroding reach, preferably on the concave (outer) side of a bend where the water is deep and the current scours silt away.
4. Depth of water: enough depth at all stages so the intake port stays submerged at low water.
5. Flood level: the structure must stand above the highest flood level (HFL) or be safe against it, and the site should be free from flood and drift damage.
6. Foundation: sound strata for the foundation of the intake tower and pipes.
7. Navigation: the site must not obstruct navigation and should not be in a navigation channel.
8. Distance and elevation: close to the treatment plant and consumers (shorter pipeline, lower cost); for gravity schemes, enough head.
9. Accessibility: access for construction, inspection and maintenance in all seasons, and nearness to power for pumping.
10. Future expansion and ownership of land/legal rights at the site.
11. Ice and silt: the site should not be affected by ice formation or heavy sedimentation.

Wet river intake

A wet intake is a tower (or well) built in the river, with its interior filled with water up to river level. Ports at different levels admit water, and the intake pipe leaves from the bottom of the well. The valves are operated from the top, since they are underwater.

  Foot bridge =====#=====
        Stem (control rod) |
  HFL ~~~~~~~~~~~~~~~~~~~~ |
  NWL ~~~~~~[port + screen]|  <- water inside
  LWL ~~~~~~[port + screen]|     well = river level
  bed ///////[port]--------|
              |   intake pipe
              +---------------> to pump well / plant

Operation and maintenance: The tower is filled with water and the pipe is always flooded. Gates at each port are operated from the bridge by a stem. Screens must be raked and cleaned from above, and divers or stop-logs are used when the tower has to be examined. It is cheaper than a dry intake, but harder to maintain.

Dry river intake

A dry intake is a tower built on the river bank (or just inside it) whose interior is kept dry. Water enters through ports in the wall, flows into a separate sump by a connecting pipe, and only the valves and pipes are in the dry chamber. The operator can work inside it at any time.

 Foot bridge ===+
                | operating floor
 HFL ~~~~~~~~~ ||   gate valves
              ||[=]---+
 NWL ~~~~~~~~ ||[=]---+--> pipe to
              ||[=]---+    sump/pump well
 LWL ~~~~~~~ ||  dry chamber
   ///////// ||____________ screens at ports
   river bed  |   (water-tight walls)

Operation

• Water flows from the river through the screened ports, then through the valves in the dry chamber, to the sump or directly to the pump.
• The operator selects the port at the best level and closes the others.
• Valves and screens can be inspected, cleaned or repaired from inside without wetting the operator.

Merits and demerits: Easy operation and maintenance, but it needs a stronger water-tight wall, deeper foundation, and is costlier than a wet intake.

Wet river intake

A wet intake is a tower (or well) built in the river, with its interior filled with water up to river level. Ports at different levels admit water, and the intake pipe leaves from the bottom of the well. The valves are operated from the top, since they are underwater.

  Foot bridge =====#=====
        Stem (control rod) |
  HFL ~~~~~~~~~~~~~~~~~~~~ |
  NWL ~~~~~~[port + screen]|  <- water inside
  LWL ~~~~~~[port + screen]|     well = river level
  bed ///////[port]--------|
              |   intake pipe
              +---------------> to pump well / plant

Operation and maintenance: The tower is filled with water and the pipe is always flooded. Gates at each port are operated from the bridge by a stem. Screens must be raked and cleaned from above, and divers or stop-logs are used when the tower has to be examined. It is cheaper than a dry intake, but harder to maintain.

Dry river intake

A dry intake is a tower built on the river bank (or just inside it) whose interior is kept dry. Water enters through ports in the wall, flows into a separate sump by a connecting pipe, and only the valves and pipes are in the dry chamber. The operator can work inside it at any time.

 Foot bridge ===+
                | operating floor
 HFL ~~~~~~~~~ ||   gate valves
              ||[=]---+
 NWL ~~~~~~~~ ||[=]---+--> pipe to
              ||[=]---+    sump/pump well
 LWL ~~~~~~~ ||  dry chamber
   ///////// ||____________ screens at ports
   river bed  |   (water-tight walls)

Operation

• Water flows from the river through the screened ports, then through the valves in the dry chamber, to the sump or directly to the pump.
• The operator selects the port at the best level and closes the others.
• Valves and screens can be inspected, cleaned or repaired from inside without wetting the operator.

Merits and demerits: Easy operation and maintenance, but it needs a stronger water-tight wall, deeper foundation, and is costlier than a wet intake.

Modification if the river bank is unstable

• Move the intake into the river away from the bank, so it stands as an isolated tower (a wet or dry tower) connected to the bank by a foot bridge, with the intake pipe laid in a protected trench under the bed.
• Provide bank protection: stone pitching or gabion, groynes, spurs or retaining walls upstream and downstream of the intake.
• Use deep, well foundations (pile or caisson) for the tower so it is not undermined by scour.
• Put the intake on the outside of a bend where the bank is naturally deeper and more stable, or train the river with training walls.
• Use a canal or channel intake (a cut leading water to the intake) if the river migrates, and build the structure sufficiently away from the moving bank.

A river intake is a structure built in a river (or on its bank) to draw water for a water supply scheme. It has ports at different levels, screens, gates or valves, an intake well or tower, and an intake pipe or conduit to the pump well or treatment plant.

   Foot bridge
  =========|===========
           |   Intake tower
 HFL ~~~~~ |  [ ]  gate/valve
           | __|__ upper port
 NWL ~~~~~ |/  |  \  <-- screens
           |   |__ middle port
 LWL ~~~~~ |   |
           |___|__ lower port
  River bed ///|\\\
              \|/ intake pipe to
                   pump well/treatment

Types

• Wet intake: the tower is filled with water; valves are operated from the top.
• Dry intake: the tower is dry; water flows through ports to a separate sump and valves are operated in the dry chamber.

Important features

• Ports at two or three levels give the clearest water in any season; bell-mouth entries and low entrance velocity (0.15 to 0.3 m/s) avoid drawing silt and debris.
• Coarse (20 to 50 mm) and fine screens (6 to 12 mm) keep out floating matter and fish.
• The structure is placed in a straight or outer bend reach with a stable bank and enough depth, upstream of pollution sources, and is made safe against floods and scour.
• Protection works (pitching, groynes) and a foot bridge for access are provided.

Maintenance: regular raking and cleaning of screens, inspection of gates and valves, and flushing silt from the well and pipe.

Factors for selecting an intake site

1. Water quantity: the source must give the design flow even in the driest season; the minimum flow must exceed the demand.
2. Water quality: the site should be upstream of towns, sewage and industrial discharges, and away from tributaries that bring silt or pollution.
3. Stable bank and bed: choose a stable, non-eroding reach, preferably on the concave (outer) side of a bend where the water is deep and the current scours silt away.
4. Depth of water: enough depth at all stages so the intake port stays submerged at low water.
5. Flood level: the structure must stand above the highest flood level (HFL) or be safe against it, and the site should be free from flood and drift damage.
6. Foundation: sound strata for the foundation of the intake tower and pipes.
7. Navigation: the site must not obstruct navigation and should not be in a navigation channel.
8. Distance and elevation: close to the treatment plant and consumers (shorter pipeline, lower cost); for gravity schemes, enough head.
9. Accessibility: access for construction, inspection and maintenance in all seasons, and nearness to power for pumping.
10. Future expansion and ownership of land/legal rights at the site.
11. Ice and silt: the site should not be affected by ice formation or heavy sedimentation.

Construction of a spring intake

A spring intake (spring box or spring capture) is a small chamber built at the spring eye to collect all the flow from the spring, protect it from pollution, and send it to the pipeline by gravity. It is the most common intake for rural hilly areas of Nepal because springs give clean water at a high level.

Parts of a spring intake

• Collection chamber (spring box) of stone masonry or concrete, with a pre-cast cover and manhole.
• Gravel filter / perforated pipes at the back wall to collect water uniformly from the spring eye.
• Outlet pipe with a gate valve (and a strainer) to the pipeline.
• Overflow pipe to take excess water; washout (drain) pipe with a valve for cleaning; vent pipe with a screen.
• Protection works: clay/impervious cap over the spring, a diversion drain (catch drain) uphill to divert surface water, a fence, and a vegetation or plantation cover.

Plan

   Diversion drain (uphill)
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  |    fence                    |
  |   +---------------------+   |
  |   | gravel filter ::::  |   |
  |   |  (spring eye)       |-->| overflow
  |   | collection chamber  |   |
  |   |  [manhole]   outlet |==>| pipe to tank
  |   +----------+----------+   |
  |         washout pipe        |
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Section / elevation

        Vent      Manhole cover
         |   ____|_____
  ground |  |          |  clay cap (0.5 m)
  =======+--+          +=============
         |  |  air     |
 Spring->|::| water lvl|--> overflow
 gravel  |::|~~~~~~~~~~|
 filter  |::|          |==> outlet+valve
         |__|__________|
              washout pipe

A spring intake must collect the whole spring yield without disturbing the natural flow or letting pollution in. The factors to be considered while constructing it are as follows.

A spring intake (spring box or spring capture) is a small chamber built at the spring eye to collect all the flow from the spring, protect it from pollution, and send it to the pipeline by gravity. It is the most common intake for rural hilly areas of Nepal because springs give clean water at a high level.

Parts of a spring intake

• Collection chamber (spring box) of stone masonry or concrete, with a pre-cast cover and manhole.
• Gravel filter / perforated pipes at the back wall to collect water uniformly from the spring eye.
• Outlet pipe with a gate valve (and a strainer) to the pipeline.
• Overflow pipe to take excess water; washout (drain) pipe with a valve for cleaning; vent pipe with a screen.
• Protection works: clay/impervious cap over the spring, a diversion drain (catch drain) uphill to divert surface water, a fence, and a vegetation or plantation cover.

Plan

   Diversion drain (uphill)
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  |    fence                    |
  |   +---------------------+   |
  |   | gravel filter ::::  |   |
  |   |  (spring eye)       |-->| overflow
  |   | collection chamber  |   |
  |   |  [manhole]   outlet |==>| pipe to tank
  |   +----------+----------+   |
  |         washout pipe        |
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Section / elevation

        Vent      Manhole cover
         |   ____|_____
  ground |  |          |  clay cap (0.5 m)
  =======+--+          +=============
         |  |  air     |
 Spring->|::| water lvl|--> overflow
 gravel  |::|~~~~~~~~~~|
 filter  |::|          |==> outlet+valve
         |__|__________|
              washout pipe

Factors to be considered

1. Spring yield: measure the minimum yield (dry season) and design the intake and the outlet for the maximum flow; overflow handles surplus.
2. Location of the spring eye: all eyes must be captured inside one chamber; the box must be on the exact eye and must not dam or divert the water (excavate carefully so that the flow is not lost to another path).
3. Foundation: put the box on firm impervious rock or hard clay and keep the back-wall open (gravel filter) to the spring while the other walls are water-tight.
4. Protection against pollution: cover with an impervious clay cap, fence off, keep animals and latrines away, and construct a diversion drain uphill.
5. Water tightness: use rich cement mortar (1:3) for walls and plaster the inside.
6. Gravel filter: graded stone or gravel at the face to hold the soil back and spread the flow.
7. Overflow and washout pipes, with the outlet pipe a little above the floor so that sediments settle.
8. Ventilation and access: vent pipe with a screen, lockable manhole.
9. Local materials and cost, since these schemes are community-managed.