THE SLOPE OF THE POND LEVEE
The slope of the pond levee, is the
gradient of the levee from the edge of the top width to the inside toe at the
bottom of the pond. It is described as the ratio between the horizontal
distance and vertical height of the dam levee. This means, for instance, that
if the distance from the inside toe to where the top width starts (edge of the
pond from above) measures 2m and the height of the dam measures 1 meter, then
the slope for that levee is 2:1.
It is recommended that pond levees
have a gentle slope of about 2:1. This however, depends on the size of the
pond. Large ponds need to have a gentler slope (see table 4.1 below)
Table 4.1: Recommended Slope for production ponds
|
Size of
Pond
|
Recommended
Slope
|
|
5 – 20 ha
|
4:1 to 7:1
|
|
1500 m2 to
5,000 m2
|
2:1 to 4:1
|
|
+150 m2 to
1,500 m2
|
2:1
|
|
≤ 150 m2
|
1.5:1 to 1:1
|
Remember,
the large the pond, the gentler the slope should be. Large ponds have a greater
surface area to perimeter ratio. This makes it possible to obtain the greater
amounts of earth needed to make gentler slope from within the ponds have a
greater surface area to perimeter ratio. The makes it possible to obtain the
greater amounts of earth needed to make gentler slopes from within the pond
during construction. Having a gentle slope is beneficial in that:
a.
A gentle slope helps break up the waves
as they hit upon the pond levee. This reduces the impact of the water waves on
the levee. Consequently, the levee is
less likely to collapse and there is less siltation of the pond. The lifespan
of the pond is also subsequently increased and maintenance costs are lower.
Better yields (in as far as the pond infrastructure is concerned) can therefore
be sustained beyond one cycle. The ability of catfish to make a deep ‘catfish
highway’ will also be minimized.
b.
It is easier and safer to enter into and
out of the pond to undertake activities such as seining. One should be able to
actually walk into and out of a pond and not have to ‘jump in and climb out’ of
the pond. The latter is dangerous for personnel.
c.
It makes it easier to seine the pond and
land the seine. Significant environmental benefits are derived when pond levees
are constructed as recommended with the appropriate slopes. There is less pond
siltation when levees are constructed as recommended.
Consequently,
there is also a reduction in the level of suspended solids in pond effluent
water. In addition, less water is required for production due to reduced
seepage.
CALL 08032861326 FOR YOUR POND CONSTRUCTION AND CONSULTANCY .
