PNS/BAFS/PAES 225:2017

Small Water Impounding System

PNS/BAFS/PAES 225:2017

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

active storage

any barrier constructed to store water

dam

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

dam height

volume below the intake structure; sediment volume based on 25 years of accumulation in the reservoir

dead storage

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

filter drain

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

homogeneous embankment

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

Karst topography

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

natural spillway

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

normal storage elevation

part of the system that impounds the runoff

reservoir

line with no filter arrangements where seepage occurs

seepage line or phreatic line

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

spillway

total capacity at normal water surface elevation

storage capacity

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

structural height

side of the embankment wetted by the impounded water

upstream face

area which contributes runoff or drains water into the reservoir

watershed

privilege granted by the government to use and appropriate water

water right

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

well-protected reservoir

dam consisting a central impervious core flanked between zones of more pervious materials

zoned embankment

Soil shall be well-graded and shall contain at least ____ clay

30%

________ should be preferred than cut spillways.

Natural spillways

Reservoir shall be at least ________ ha at normal water level.

1 ha

Watershed: It shall have a maximum slope of _____

18%

A profile cross-section of the stream/depression at the selected site _____ m upstream and ____ m downstream shall also be included.

20; 20

Agrohydrologic Analyses includes

Run-off and inflow hydrograph, Field water balance, Reservoir inflow

The minimum crest width for maintenance purposes is _____.

4 m

Type of Suitable Dam: This type shall be considered if the supply of materials of low permeability such as sandy or silty clay and other clayey material is abundant.

Homogeneous/Modified Homogeneous Type

Type of Suitable Dam: This type shall be considered if sufficient quantities of both pervious and impervious materials are available.

Zoned Type

Embankment Slopes: Upstream Face

2.75:1

Embankment Slopes: Downstream Face

2.5:1

The minimum thickness shall be_____.

20 cm

The downstream face shall be protected by using _____.

grass sodding

The upstream face shall be protected by using _____.

plain gravel

The rock toe height

1/3 of hydraulic head

Embankment shall be compacted by layers of _____ with proctor density of ____.

20 cm; 95%

maximum surcharge height for spillway

1m

Type of spillway

side channel or chute type spillway

height

5 to 15 m

service area

25 to 150 ha