Geoscience Reference
In-Depth Information
The increase in the cultivation of annual crops in contrast to perennials in
hilly regions also causes damage to roads through increased erosion and
rainfall run-off ratios (Piyasiri 2009). The loss of multipurpose reservoir
capacity as a result of sedimentation is a major off-site effect. This loss
has a major adverse impact on power generation and on the irrigation of
agricultural land in the dry zone outside Sri Lanka's Central Highlands.
Land degradation has been recognized as the most serious
environmental problem especially in the highlands of the country. A
high population density, presently over 300 per km, and a lack of off-
farm livelihood opportunities has led to excessive highland exploitation
(Ministry of Environment 2010). In the higher elevations in Sri Lanka's
Central Highlands, particularly due to the cultivation of tobacco, potato,
and vegetable crops and the construction of roads and highways, soil
erosion has been taking place to a considerable extent. The degrees of soil
erosion extend up to massive land sides. When the same land is planted
continuously with the same crop, soil fertility tends to gradually decrease
while the application of fertilizes and agro-chemicals further challenge
the soil. Due to tillage and pulverizing soil clods, sudden heavy rains,
soil erosion, landslides, and the deposition of clay and silt, the reservoirs
designed to supply water to hydropower in the region are under great risk.
According to the H.R. Wallinford Limited completed hydrographic survey
(Hewawasam 2010), sedimentation rates in small reservoirs of the Upper
Mahaweli catchment for the period from 1985 to 1993 in the Polgolla barrage
has reduced its storage capacity to 56% over a 17 year period. Rantambe
reservoir has reduced its storage capacity to 72% during a three year period
after impoundment (Table 15.2).
Table 15.2. Original capacity, surveyed capacity and percentage of loss of original capacity
due to siltation of hydropower reservoirs impounded in the upper Mahaweli Catchment.
Name
of the
reservior
Year of the
impoundment
Original
capacity
(Million m 3 )
Year of the
hydrographic
survey
Surveyed
capacity
(Million m 3 )
The loss of
original capacity
due to siltation
Kotmale
1985
176.770
1990
184.640
-
Polgolla
1976
5.271
1993
2.794
44%
Victoria
1985
717.530
1993
713.080
01%
Rantembe
1991
10.950
1994
7.900
28%
Source: Wallingford 1995.
Population growth and urbanization
Sri Lanka's Central Highlands mainly cover four administrative districts:
Kandy, Nuwara Eliya, Matale, and Badulla. The total population of these
four main districts is around 3.3 million and its population density is around
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