Factors in constructing a spring intake

A spring intake must collect the whole spring yield without disturbing the natural flow or letting pollution in. Its parts and layout are shown first, followed by the factors to be considered while constructing it.

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 (dry-season) yield to check that it meets the demand, and size the chamber and pipes for the maximum flow; the overflow takes the surplus.
2. Location of the spring eye: all eyes must be captured inside one chamber; the box must sit on the eye itself and must not dam the water back (the water level in the box must stay below the eye, or the spring may find another path and be lost); excavate carefully.
3. Foundation: put the box on firm impervious rock or hard clay and keep the back wall open to the spring (through the gravel filter), 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: place the outlet pipe a little above the floor so that sediment settles below it and is flushed out through the washout.
8. Ventilation and access: a screened vent pipe and a lockable manhole.
9. Local materials and cost, since these schemes are community-managed.