Introduction - Runoff Prediction in Ungauged Basins: Synthesis across Processes, Places and Scales - page 2

Table 1.1. Need for runoff predictions in ungauged basins

Hydrological problem Water management purpose

How much water do we have? Water allocation, long-term planning, groundwater recharge
When do we have water? Water supply and hydropower production, planning of restoration measures
For how long do we have water? Ecological purposes, hydropower potential, industrial and domestic
water supply, irrigation
How dry will it be? Environmental flows for ecological stream health, drought management, river restoration,
assessing dilution of effluents
How high will the flood be? Design of spillways, culverts, dams, dam removal, levees, reservoir management, river restoration,
risk management
What are the dynamics of runoff? All of the above plus water quality (sediments, nutrients) predictions

Figure 1.2. The online model
that predicts runoff from the
Luangwa River basin into the
Zambezi, just upstream from Cahora
Bassa Reservoir.

operational since 2009 and gives hourly updates of runoff
estimates. The runoff is very substantial compared to the
average outflow of the Cahora Bassa Dam, and so these
predictions can indeed make a difference between life and
death, early warning and forced displacement. It shows the
direct relevance of PUB for society.
The challenges in the routine management of the Cahora
Bassa Reservoir demonstrate the importance of runoff
predictions for reservoir management, but there are many
other purposes for which runoff predictions are needed.
Flood predictions are needed for the design of spillways,
culverts, dams, levees, reservoir management, river restor-
ation and risk management. Low flow predictions are
needed for determining environmental flows for ecological
stream health, drought management, river restoration and
assessing the dilution of discharges into a stream. Table 1.1
illustrates the range of problems for which runoff predic-
tions in the context of integrated water resources and risk

management are needed. All of them have direct societal
relevance (Carr et al., 2012 ). Clearly, runoff predictions
are important to a large part of humanity.
Unfortunately, in most catchments around the world,
runoff is not measured. In any given region, in any part
of the world, only a fraction of the catchments possess a
stream gauge where water levels are gauged, which are
then transformed into runoff, i.e., the volume of water per
unit time that flows through a cross-section of a stream. All
the other catchments have no stream gauge, and so are
ungauged, and yet runoff information is needed almost
everywhere people live for the multitude of purposes out-
lined above.
The only recourse is therefore to predict runoff in these
catchments or locations using alternative data, or infor-
mation or knowledge. How one can predict runoff for these
ungauged catchments and how well one can do this are the
subject matter of this topic.