15 Introduction to and General Aspects of Water Management
335
15.3.3 Upstream-downstream interrelationships in river basins
For river basin planning and management, basic knowledge on the upstreamdownstream interrelationships is required. Hydrologic responses between headwaters,
central basin area and the floodplain delta or estuaries are unique in every basin and
their knowledge is essential for downstream long-term water use, distribution and
planning. Transport and delivery of sediment from catchments are important for both
downstream and within-basin considerations. Relationships between the magnitude
of sediment yield of basins and climatic, physiographic and land use controls have
been investigated by many researchers (Hadley et at, 1985). Knowledge of the
distribution of sediment sources and sinks within a basin is essential for recommending control measures. In general, upstream areas and watersheds may be subject to
important man-induced land use changes or conversions (e.g., deforestation), which
might affect downstream hydrology. Occurrence of natural phenomena such as fast
geologic erosion processes (i.e., mass wasting), volcanic or seismic activities can also
influence the hydrologic behavior of river basins to a certain extent.
An example from Sulawesi (Verstappen, 1977), illustrates the use of remote sensing, i.e., stereo aerial photography, for detecting changes in a river regime of a
tropical catchment. The deforestation in the catchment of the river, shown in Fig.
15.2, has led to an important change in the river morphology which changed from a
meandering river (note the remnants on the floodplain) to a braiding river (the present
one). The wavelength, the width and the gradient all have increased, the sinuosity, the
radius of curvature and the meander amplitude have decreased. The cause of the
changes is the sharp increase in the sediment load of the river. The width to depth
ratio has increased and also in absolute terms the depth of the river may be less than
during the former meandering state. Attenuation of the peak flows by overbank flow
still take place and it is therefore difficult to conclude whether the peak flows have
increased or not. However, the higher discharges may have become more irregular.
The image provides a diagnosis for profound changes in the regime of the river during
recent times.
The next example illustrates the use of remote sensing to analyze upstreamdownstream processes in tropical river basins. In the lowland part of large river
basins, a combination of three processes may affect long term developments, i.e., a
rise of the sea level as a result of global warming, a change of river regimes caused
by upstream processes, such as deforestation and urbanization, and tectonic movements. The synoptic view of small-scale satellite imagery allows for the identification
of tectonism and a zonation of areas which could be affected in the near future. At
least a direction is given by the image interpretation for ground-based studies. The
image of Fig. 15.3, a Landsat MSS infrared band shows such a region, the Musi river
(M) and the inland Komering delta near Palembang (P), South Sumatra, Indonesia.
The inland delta was formed after tectonic subsidence of a graben and after sea level
rise during the Holocene (approx. the last 10.000 years). The faults (F) are indicated
on the image. The neo-tectonism is also expressed by the east-west oriented drainage
pattern (H) on the adjoining horst (uplifted and tilted block) whereas the Komering
(K) river flows from west to east through the horst. The inland delta consists oflarge
335
15.3.3 Upstream-downstream interrelationships in river basins
For river basin planning and management, basic knowledge on the upstreamdownstream interrelationships is required. Hydrologic responses between headwaters,
central basin area and the floodplain delta or estuaries are unique in every basin and
their knowledge is essential for downstream long-term water use, distribution and
planning. Transport and delivery of sediment from catchments are important for both
downstream and within-basin considerations. Relationships between the magnitude
of sediment yield of basins and climatic, physiographic and land use controls have
been investigated by many researchers (Hadley et at, 1985). Knowledge of the
distribution of sediment sources and sinks within a basin is essential for recommending control measures. In general, upstream areas and watersheds may be subject to
important man-induced land use changes or conversions (e.g., deforestation), which
might affect downstream hydrology. Occurrence of natural phenomena such as fast
geologic erosion processes (i.e., mass wasting), volcanic or seismic activities can also
influence the hydrologic behavior of river basins to a certain extent.
An example from Sulawesi (Verstappen, 1977), illustrates the use of remote sensing, i.e., stereo aerial photography, for detecting changes in a river regime of a
tropical catchment. The deforestation in the catchment of the river, shown in Fig.
15.2, has led to an important change in the river morphology which changed from a
meandering river (note the remnants on the floodplain) to a braiding river (the present
one). The wavelength, the width and the gradient all have increased, the sinuosity, the
radius of curvature and the meander amplitude have decreased. The cause of the
changes is the sharp increase in the sediment load of the river. The width to depth
ratio has increased and also in absolute terms the depth of the river may be less than
during the former meandering state. Attenuation of the peak flows by overbank flow
still take place and it is therefore difficult to conclude whether the peak flows have
increased or not. However, the higher discharges may have become more irregular.
The image provides a diagnosis for profound changes in the regime of the river during
recent times.
The next example illustrates the use of remote sensing to analyze upstreamdownstream processes in tropical river basins. In the lowland part of large river
basins, a combination of three processes may affect long term developments, i.e., a
rise of the sea level as a result of global warming, a change of river regimes caused
by upstream processes, such as deforestation and urbanization, and tectonic movements. The synoptic view of small-scale satellite imagery allows for the identification
of tectonism and a zonation of areas which could be affected in the near future. At
least a direction is given by the image interpretation for ground-based studies. The
image of Fig. 15.3, a Landsat MSS infrared band shows such a region, the Musi river
(M) and the inland Komering delta near Palembang (P), South Sumatra, Indonesia.
The inland delta was formed after tectonic subsidence of a graben and after sea level
rise during the Holocene (approx. the last 10.000 years). The faults (F) are indicated
on the image. The neo-tectonism is also expressed by the east-west oriented drainage
pattern (H) on the adjoining horst (uplifted and tilted block) whereas the Komering
(K) river flows from west to east through the horst. The inland delta consists oflarge