Environmental Engineering Reference
In-Depth Information
2.3
The study area
The study area is located in the upper reaches of Lilongwe River, between the
Dzalamayama Forest Reserve and the water abstraction point for the city of Lilongwe.
The area has got three main rivers that flow through out the year. The Lilongwe River is
the main river and the other two - Lisungwi and Likuni Rivers - are its tributaries (Fig.
11.2).
Other smaller streams only flow later in the year when the rainfall has started. There is
no recent data, with respect to water flows, recorded by the Hydrology section of the
Ministry of Water Development for neither the Lilongwe River nor its tributaries.
SAFEGE (2001) gives the average flows for the three rivers as being 0.995 m
3
/s for the
Lilongwe River after the Likuni confluence and 0.24 m
3
/s for Likuni tributary.
Most of the catchment area is gently or very gently sloping, and is intensively
cultivated. Almost all the natural forest has been cleared for agriculture. The only
significant areas of forest are found in the Dzalanyama Forest Reserve towards the
international border with Mozambique, upstream of the study area.
Lilongwe district like all other areas in the central region of Malawi has a dry season
and a rainy season. The rainy season lasts no more than six months from November to
April. There is no rainfall in the last half of the year. Data from the department of
Metrological Services shows that the average rainfall in the district is of the order of 600-
1200 mm per year. Average temperatures range from a minimum of 6
o
C in winter to a
maximum of 30
o
C in summer.
The land use patterns in the study area and the location of the sampling points,
denominated with capital letters from A to F, are presented in Figure 11.2. The Lilongwe
River drains the Dzalanyama catchment. The drainage area is about 1800 km
2
. The
Katete, Lisungwi, and Likuni Rivers are tributaries of the Lilongwe River and originate
within the catchment. A large portion of the land has been used for agriculture with
different types of crops grown.
Along the Lilongwe River, two dams have been constructed namely Kamuzu Dams I
and II (Dam I and Dam II). Dam I was constructed in 1966 and Dam II was constructed
in 1999. The primary purpose of these dams is to provide the water supply of the city of
Lilongwe. The flow downstream of Dam II is regulated to meet the demands of the
downstream users. The capacity of Dam I was initially 4.5 Mm
3
, but has been reduced
significantly due to deforestation and reduced land cover that has exposed the soil to
erosion. The Dam II capacity is 19.8 Mm
3
with a 1 in 200-year return period.
Downstream of the dams, the river passes through an area of rural pattern settlements.
Most people in the area rely for their survival on subsistence agriculture. Few families are
completely self-sufficient in food production. Crops grown in the area include: tobacco,
paprika, vegetables, maize and groundnuts. Other typical economic activities in the area
include brick making and the brewing of beer in the form of informal sector economic
activities, as described in Chapter 5.
Informal villages and squatter settlements have emerged along the riverbanks during
the last decade, and their presence is pronounced between Dam II and the abstraction
point (E) of the Lilongwe Water Board Water Treatment Works (LWBWTW), which is
the main source of the potable water supply for the City. The settlements are not provided
