PNS/BAFS/PAES 226:2017

Small Farm Reservoir

PNS/BAFS/PAES 226:2017

height

less than 5m

pond area

1500 sqm

actual height of the embankment after settlement

designed height

height of the embankment to be attained during construction

finished height

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

freeboard

slope of the upstream face of the embankment

inside slope

slope at the downstream face of the embankment

outside slope

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

storage ratio

rainfall pattern with five wet months of more than 200 mm/month, five dry months of less than 100 mm/month, two transition months of 100mm200mm/month and total annual rainfall above 1500 mm.

unimodal rainfall pattern

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.

Straight Embankment

On slightly sloping land, the excavated earth can be used to impound some water above ground level.

Rectangular Balanced Excavation

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

Dugout Pond

slopenf for straight embankment

2-15%

slope for rectangular balanced embankment

storage ratio for straight embankment

2 to 7

storage ratio for recatngualr balanced embankment

1.5 to 2.5

storage ratio for dugout embankment

1

The reservoir shall be located in areas with slope

0 to 15%

The soil texture within ____ of the soil profile shall be loam, sandy loam, clay loam or sandy clay loam

1.5 m

minimum depth of soil profile to be analyzed

1.5 m

Minimum size of catchment area for terraced land

0.2 to 0.5 ha per 1000 sqm reservoir capacity

Minimum size of catchment area for grassland/residential

0.6 to 1.0 ha per 1000 sqm reservoir capacity

The finished height (H’) should be ____ higher than the designed height (H) to provide allowance for the settlement of the embankment.

20%

inside slope

3 is to 1

outside slope

2 is to 1

The width of the crest can range from

2 to 3 m

The depth of the diversion channel shall be at least ______ and the width shall be _____ the depth or wider.

0.75 m; twice

The reservoir shall be desilted ______.

annually