PUB in practice: case studies - Runoff Prediction in Ungauged Basins: Synthesis across Processes, Places and Scales - page 337

measurements with a tension infiltrometer in compacted
soils would provide valuable infiltration model parameter
estimates. Finally, this study forms the basis to modify
AGWA look-up tables (transferrable

(Mazvimavi, 2003 ). The objectives of the study were (i)
to assess the potential of using river basin descriptors for
predicting flow statistics; (ii) to examine the possibility of
delineating basins into hydrologically homogeneous
groups and to assess if such grouping improves prediction
of flow statistics; and (iii) to examine if the parameters of
selected rainfall

parameters)
for developed infiltrating areas, which will extend the cap-
ability to apply KINEROS2 to this type of land use.

' regional '

- runoff models can be regionalised using

basin descriptors.

11.17 RUNOFF PREDICTIONS TO
HELP MEET MILLENNIUM
DEVELOPMENT GOALS IN
ZIMBABWE
d. mazvimavi

Description of the study area
The study was conducted on 52 river basins in Zimbabwe
( Figure 11.70 ), which is located in Southern Africa and
covers a land area of 390 757 km 2 . Altitude varies from
162 to 2592 m a.s.l. The elevation increases from both the
south and north towards the central part of the country,
which defines many of the catchments. The northern part
of the country has the Gwayi, Manyame and Mazowe
Rivers draining into the Zambezi River. Rivers on the
southern part drain into the Limpopo River, which is
shared with Botswana, South Africa and Mozambique.
The Eastern Highlands, which have an elevation of
1800 - 2592 m, lie along the border with Mozambique.
All the rivers in Zimbabwe eventually become part of
trans-boundary rivers and introduce the special challenge
of sharing hydrological data between the respective
countries.
Zimbabwe has a tropical climate with one wet season
and one dry season. However, areas of high elevation
experience sub-tropical to temperate conditions. The wet
season is from mid-November to mid-March, with the rest
of the year being dry. Most of the rainfall occurs in the
form of isolated thunderstorms with high intensity. This
poses a problem for accurately measuring areal rainfall
using a sparse network of rainfall stations. The spatial
variation of rainfall is greatly influenced by altitude and
distance from moistures sources such as the Indian Ocean
on the east. Rainfall increases from west to east, and from
the low-lying southern parts to areas at high elevation
along the central part and the Eastern Highlands. The
southern low-lying areas receive about 350 to 600 mm/yr
of rainfall, while the central catchment receives 700

The issue from societal and hydrological perspectives
The sustainable planning and management of water
resources requires knowledge on the availability of these
resources and their spatial and temporal variability. This
information is generally derived from gauging networks
monitoring the various components of the water cycle. In
some river basins, particularly those in Africa, these
networks show many gaps, including those basins ear-
marked for the development of water resources. The
reasons for the inadequate coverage are many. They
include inadequate funding and personnel with relevant
expertise; poor accessibility of some of the basins; and
disfunctionality of institutions due to conflicts. Lack of
adequate hydrological data contributes towards ill-
designed infrastructure that does not provide the planned
benefits. Without information about the spatial and tem-
poral variability of the water resources, the potential and
constraints in developing these resources are not well
understood.
The international community, through the Millenium
Development Goals, expressed a commitment to improv-
ing human wellbeing through creating and diversifying
livelihood options, including increasing access to potable
water. Some of the measures for improving human well-
being include increasing food production. These efforts
will inevitably increase water demand and the competition
for water among various user groups. Sustainable water
resources management requires balancing the water
demand with the natural renewal rate of water. This
requires information about the availability of water, which
is impossible to estimate in ungauged river basins. Tools
for improving predictions in river basins with inadequate
data are therefore necessary to provide the information
necessary for satisfying societal needs for water.
This study carried out in Zimbabwe had the aim of
improving prediction of river flow statistics used routinely
for water

-

1200

-

mm/yr. The highest rainfall, 1200 2000 mm/yr, is received

on the Eastern Highlands. Most parts of the country fall
within the semi-arid zone. Areas receiving low rainfall,
such as the southern and western parts, have high inter-
annual variability of rainfall with a coefficient of variation
of 30 - 40%; the coefficient is 20 - 30% in other parts of the

country.
There are about 450 river gauging stations, mostly in
the developed central part of the country ( Figure 11.71 ).
The earliest stations were developed during the 1920s.
A considerable number of river flow measuring stations

resources planning in ungauged basins