rise in maximum flood level from the original unobstructed flood level which result after an obstruction to the flow such as a dam, has been introduced

structure or weir provided across the river or creek to raise its water level and divert the water into the main canal to facilitate irrigation by gravity.

occurs when a thin sheet of incoming flow moving at high velocity strikes water of sufficient depth

The different types of diversion dams and suitability in site conditions are

a weir with a surface that slopes gently downward from the crest to the downstream apron where only the horizontal component of the overflow jet takes part in the impact with the tailwater while the vertical component is unaffected

a weir produce free discharging flows and dissipates overflowing water jet with the impact in the downstream apron - not adaptable for high drops on yielding foundation

a weir produce free discharging flows and dissipates overflowing water jet with the impact in the downstream apron - not adaptable for high drops on yielding foundation

a weir where the larger part of the ponding is accomplished by the solid obstruction or the main body of the weir

weir with sloping upstream and downstream slopes which allow boulders and debris roll over and hot the downstream apron with less impact

used to stabilize the river bed for intake type diversion structures or to gain a limited amount of diversion head the external part of the weir exposed to water flow is made of pure concrete while the inside part is filled with stones and cobbles which provides a more economical section

- a weir wherein the upper curve of the ogee is made to conform to the shape of the lower nappe of a ventilated sheet of water falling from a sharp-crested weir - has a high discharge efficiency

stones wrapped in wire fence meshes for added stability and strength

small barrier built across the direction of water flow on shallow rivers and streams intended to convey runoff during peak flow and to slow and hold surface water long enough for the water to deposit sediment it is carrying; facilitates irrigation by using the upstream bay of the dam as pump sump

internal erosion induced by regressive erosion of particles from downstream and along the upstream line towards an outside environment

dam that relies on rock, either dumped in lifts or compacted in layers, as a major structural element where an impervious membrane is used as the water barrier and can be placed either within the embankment or on the upstream slope

composed of semi-pervious materials

The interior section of a rockfill dam is typically divided into zones depending on the range of variation in the character and gradation of the available material.

consists of a well-graded mixture of hard and durable particles, and slightly weathered to fresh rock to secure the stability of dam body.

composed of impervious blanket usually made of cohesive soil or non-cohesive silt and is covered for protection.

Components of Rockfill Dam

area capable of being irrigated, principally as regards to availability of water, suitable soils, and topography of land

area capable of being irrigated, principally as regards to availability of water, suitable soils, and topography of land

Annex B Dam instrumentation provide data on the water pressure at selected points within an embankment dam or foundation

maximum area which an irrigation project can serve considering the extent of arable lands and the available water supply

Annex B Dam instrumentation surface monuments placed on the dam crest and slopes to measure long term settlement and horizontal deflection

maximum average contact pressure between the foundation and the soil which should not produce shear failure in the soil

method to determine the rate of flow under laminar flow conditions through a unit cross sectional are of soil under unit hydraulic gradientmethod to determine the rate of flow under laminar flow conditions through a unit cross sectional are of soil under unit hydraulic gradient

Annex B Dam instrumentation usually installed in a large dam or its vicinity to measure the effects of strong earthquakes and seismic activity at the site

Annex B Dam instrumentation measure the total seepage and the seepage from selected locations.

occurrence or frequency of earthquakes in a region

Annex B Dam instrumentation measure internal settlements in an embankment dam and in foundations

The only designed suited to flat areas. A reservoir is constructed by excavating the earth leaving storage space space that can be filled with water.Water is stored below the ground level and pumping is required to draw out water. slope - (flat) storage ratio - (1.0)

On slightly sloping land, the excavated earth can be used to impound some water above ground level. On higher slope it can be designed so that all water is stored above service level. Slope <2% 2-12% ratio (1.5 - 2.5)

Different types of Reservoir

ratio of the storage capacity to the total earth volume required for embankment construction which indicates the relative cost of the different types of reservoir

slope of the upstream face of the embankment

height of the embankment to be attained during construction

Water is impounded against the slope behind a semicircular embankment. Slope (4.7%) ratio (2.5-4.0)

Suited to an area with an undulating topography. A dam is built across a valley and water is impounded on the upstream side of the dam. Slope- (2-15 %) Storage ratio - (2-7)

4 Main Components The main components of a small farm reservoir are

Slope at the downstream face of the embankment

additional height of the dam provided as a safety factor to prevent overtopping by wave action or other causes

actual height of the embankment after settlement

volume of water stored in reservoir between the minimum water level and normal water level

any barrier constructed to store water

Vertical distance from lowest point of the ground line to the dam crest

Volume below the intake structure computed as V=20900 x A ^ 0.687 where A= drainage area,km sediment volume based on 25 years of accumulation in the reservoir

dam component which prevents migration of small particles and screen off fine materials that flow with seepage water and prevent piping

dam composed of a single kind of embankment material exclusive for slope protection

Geological formation shaped by the dissolution of the layer or layers of soluble bedrock, usually carbonate rocks such as limestone or dolomite.

spillway which is not excavated such as natural draw, saddle or drainage way

maximum elevation the water surface which can be attained by the dam or reservoir without flow in the spillway

phreatic line line with no filter arrangements where seepage occurs

part of the system that impounds the runoff

channel which releases surplus or flood water which cannot be contained in the active storage space of the reservoir

total capacity at normal water surface elevation

vertical distance measured from the top of the dam down to the bedrock

side of the embankment wetted by the impounded water

area which contributes runoff or drains water into the reservoir

privilege granted by the government to use and appropriate water

reservoir where the upper reaches of the basin is shielded by high mountain barriers