Lecture 12 Flashcards
a technology used for collecting and storing
rainwater for human
Rainwater Harvesting
Rainwater harvesting has
been practiced for more than _____
4000 years
defined as the method for inducing,
collecting, storing and conserving local surface runoff for agriculture in arid and semi-arid
regions.
Rainwater Harvesting
method of collecting surface runoff from a
small catchment area and storing it in the root zone of an adjacent infiltration basin.
The basin is planted with a tree, a bush or with annual crops.
Micro-catchement water harvesting
also called harvesting from external catchments is
the case where runoff from hill-slope catchments is conveyed to the cropping area
located at foothill on flat terrain.
Macro-catchment water harvesting
defined as the collection and storage
of creek flow for irrigation use.
Flood water harvesting
Also known as large catchment water harvesting or Spate irrigation
Flood water harvesting
The water flow is dammed and as a result, inundates the valley bottom of the flood plain. The water is forced to
infiltrate and the wetted area can be used for agriculture or pasture improvement.
Flood water harvesting within stream bed
The wadi water is forced to leave its natural course and conveyed to nearby cropping field
Flood water diversion
new term and employed to
cover traditional as well as unconventional ways of ground water extraction.
Groundwater harvesting
Examoles of groundwater hatvesting techniques
Qanat system,
underground dams
Special types of wells
Fine examples of groundwater harvesting
Subsurface dams
Sand storage dams
includes runoff harvesting, flood water harvesting and groundwater harvesting.
Water harvesting techniques
This method involves the construction of bunds on the contour of the
catchment area
Contour bunds
These bunds hold the flowing surface runoff in the area located
between two adjacent bunds.
Contour bunds
The height of contour bund generally ranges from
0.30 m to 1.0 m
Length of contour bunds
10 to a few 100 m
This type of structure consists of an earthen impartment constructed in
the shape of a semicircle
Semicircular hoop
Height of hoops
0.1 to 0 .5m
Radius of the hoop
5 to 30 m
Such bunds also consist of an earthen embankment, constructed in the
shape of trapezoids.
Trapezoidal bunds
also referred as off contour bunds. They consist of earthen or
stone embankments and are constructed on a land with a slope range of 0.5 to 2%
Graded bunds
Slope for graded bunds
0.5 to 2%
Height of graded bunds ranges from
0.3 to 0.6 m
are the exposed rock surfaces, used for collecting the
runoff water in a part as depressed area.
Rock catchment
Area of rock carchment
100 m² to 1000 m²
large area of ground is used as catchment for runoff
yield.
Ground catchment
Also called roaded catchment
Ground catchment
constructed by excavating the soil from the ground
surface. These ponds may be fed by ground water or surface runoff or by both
Dugout ponds
Land slope needed in dugout ponds ___ and depth from groundwater surface ____
4% and 1.5-2 m
These types of reservoirs are constructed by forming a dam
or embankment on the valley or depression of the catchment area
Embankment type reservoir
mainly meant to store the surface water for
irrigating the crops. The capacity is decided based on the amount of input water available
and output water desired.
Irrigation dam
detain the silt load coming
along with the runoff water from the catchment area and simultaneously to harvest water.
Silt detention dam
Such dams are located at the head of the valley to form the shape of a
water tank or pond
High level dam
constructed for multi-purpose objectives, such as for irrigation,
live-stock, water supply to the cattle feed, fish production etc.
Farm pond
These dams are generally constructed at the valley head, without the
provision of checking the percolation loss.
Percolation dam
These are long low rock dams across valleys slowing and spreading floodwater as well as
healing gullies
Permeable rock dams
this method, runoff water is
diverted to the area covered by graded bund by constructing diversion structures such as
diversion drains.
Water spreading bunds
The reservoirs constructed at suitable sites for controlling the flood
are known as flood control reservoirs. They are well equipped with self-operating
mechanical outlets for letting out the harvested water into the stream or canal below the
reservoir as per requirement.
Flood control reservoir
consists of a long tunnel or conduit leading from a well dug at a
reliable source of groundwater (the mother well)
Qanat systems
