water suppy - well design Flashcards
the quantity of water that is needed by the population to be covered.
The water to be supplied should be sufficient to cover both existing and future consumers. In addition to the
projected consumptions, an allowance for non-revenue water (NRW) that may be caused by
leakages and other losses should be included.
Water Demand
This level provides a protected well or a developed spring with an outlet, but without a distribution system.
The users go to the source to fetch the water. This
is generally adaptable for rural areas where affordability is low and the houses in the intended
service area are not crowded. A Level I facility normally serves an average of 15 households
within a radius of 250 meters.
Level I (Point Source)
This type of system is composed of a
source, a reservoir, a piped distribution network, and communal faucets.
Usually, one faucet
serves four to six households within a radius of 25 meters. It is generally suited for rural and
urban fringe areas where houses are clustered in sufficient density to justify a simple piped
system. The consumers still go to the supply point (communal faucet) to fetch the water.
Level II (Communal Faucet System or Stand Post)
This system includes a
source, a reservoir, a piped distribution network, and individual household taps.
It is generally suited for densely populated urban areas where the population can afford individual
connections.
Level III (Waterworks System or Individual House Connection)
- Design Period
- Design Population
- Population Growth Factor
- water consumption
- non-revenue water
Factors included in Water Demand Computation
– the span of time in which the initial capital outlay and succeeding outlays for expansion and rehabilitation can be rationally recovered.
Design Period
the targeted number of people that the project will serve.
Design Population
– the amount of water that is produced but not billed as a result of leaks, pilferages, free water, utility usages, etc. The water demand
projection should assume that the NRW of the new system will be fifteen percent
(15%) of the estimated consumptions. The plan’s figure can be increased up to a
total of 20% at the end of 10 years. These assumed NRW figures require good
maintenance of utilities, pro-active leakage prevention, and no illegal
connections for 100% recovery of supplied water.
Non–Revenue Water
After the demand has been estimated, the next step is to look for a source
that passes both the quantity and quality requirements.
Factors considered when choosing water source:
* Adequacy
* Quality
* Cost
* Legality
* Politics
Water Resources
a product of water vapor that has risen due to evaporation and accumulated
in the atmosphere , which condenses and falls on the Earth’s surface. As the water vapor
that has accumulated in cloud formations condenses, it forms drops of rain that fall to
the Earth.
Rainwater
() is exposed to the atmosphere and subject to surface runoff. It comes from rains, surface runoff and groundwater, and includes rivers, lakes, streams, ponds, impounding reservoirs, seas, and oceans. The quantity of surface runoff
depends on a large number of factors; the most important of which are the amount and
intensity of rainfall, the climate and vegetation, and the geological, geographical, and
topographical features of the catchment area. The quality of surface water is determined
by the amount of pollutants and contaminants picked up by the water in the course of
its travel. While flowing over the ground, surface water collects silt, decaying organic
matter, bacteria and other microorganisms from the soil. Thus, all surface water sources
should be presumed to be unsafe for human consumption without some form of
treatment.
Surface Water
the portion of rainwater which has percolated beneath the ground
surface to form underground deposits called aquifers. The upper surface of ()
is the water table. () is often clear, free from organic matter and bacteria due
to the filtering effect of soil on water percolating through it. However, groundwater
almost always contains minerals dissolved from the soil. () is often better in
quality than surface waters, less expensive to develop for use, and usually provides more
adequate supply in many areas in the country.
Groundwater
is a point where groundwater flows out of the ground, and is thus where
the aquifer surface meets the ground surface. A spring may be ephemeral
(intermittent) or perennial (continuous). () can be developed by enlarging
the water outlet and constructing an intake structure for water catchment and
storage.
Spring
is a hole constructed by any method such as digging, driving, boring, or
drilling for the purpose of withdrawing water from underground aquifers. ()
can vary greatly in depth, water volume and water quality. () water typically
contains more minerals in solution than surface water and may require treatment
to soften the water by removing minerals such as arsenic, iron and manganese.
() water may be drawn by pumping from a source below the surface of the
earth. Alternatively, it could be drawn up using containers, such as buckets that
are raised mechanically or by hand.
Well
() are horizontal wells, constructed by digging
a trench into the water-bearing sand and installing perforated pipes in it. Water
collected in these pipes converges into a “well” from which it is pumped out.
Infiltration Well
() would be an immediate resource to augment the existing water supply systems by “catching water wherever it falls”. () can be utilized
as an important source of water supply in areas where rain is well distributed
throughout the year and where surface and groundwater are scarce.
Rainwater
() are outcrops of groundwater that often appear as small water holes or wet spots at the foot of hills or along river banks. To obtain satisfactory water, it is
necessary to find the source, properly develop it, eliminate surface water intrusion,
and prevent animals from gaining access to the spring. There should be no immediate
upstream settlements, as these would pose the risk of biological contamination.
Springs
An () involves a simple means of obtaining naturally filtered water. It consists of a system of porous, perforated, or open-joint pipe or
other conduit that drains to a receiving well. The pipe is surrounded by gravel and is
located in a porous formation such as sand and gravel below the water table. The
collecting system should be located 6 m or more from a lake or stream or under the
bed of a stream or lake. It is sometimes found desirable, where possible, to carefully
place a cofferdam, cutoff wall, or puddle clay dam between the collecting conduit and
the lake or stream to form an impervious wall. It is not advisable to construct an
infiltration well unless the water table is relatively stable and the water intercepted
is free of pollution. The depth of the collecting pipes should be about 3 m below the
normal ground level, and below the lowest known water table, to assure a greater
and more constant yield.
inflitration wells
() supplies include water from streams, rivers, lakes, ponds, seas and oceans. () usually contains organic and inorganic
minerals and needs expensive water treatment. Unless () is the only
option, () **should be avoided for rural water supplies. **
Surface water
A () **is a hole which has been dug, bored, driven or drilled beneath the ground for the purpose of extracting ground water. **
The first step in considering the use of wells as the sources of water supply is to
calculate the total capacity of the existing wells, and compare this capacity to the
demand for water based on the population to be served. The supply-demand analysis
shows whether the existing wells can still be utilized or if new wells are needed.
production well
beneath the ground, most rocks and soil contain voids, pores or fissures.
Subsurface water, which fills these voids and pores, occurs in two zones.
Well Hydrology
lies immediately beneath the ground surface and
contain both water and air in the voids and pores.
Unsaturated zone
where the voids are all filled with water. Water in the
saturated zone is referred to as groundwater or aquifer.
Saturated zone
the boundary between the unsaturated zone and the saturated zone. The () is not stationary. It moves up during rainy
season when percolation is high and moves down during dry season
when groundwater discharge is higher. In general, the shape of the water
table tends to follow the topography of the land.
Water table
