16 Flood Forecasting and Control
359
quickly in order to guarantee a reasonably long forecast leadtime. Figure 16.2
shows this problem. As can be seen from the figure the input does not consist of
observed rainfall/snowmelt only but also of forecast rainfall in the near future.
This means that a flood forecast requires observed rainfall until the time of the
forecast plus forecast rainfall, both of which are used as input into a rainfall-runoff
model, which produces the required real-time flood forecast. As will be shown
later both, observed rainfall and rainfall forecast can be computed with the aid of
remote sensing data.
Input
System
Output
-- ---- -
1- - - - - - -
1-- - - - - -
River
Forecast
Rainfall
Catchment
Flood
Hydrograph
I
Input.
a) rainfall measured by Radar
b) forecast rainfall
Rainfall
past - - C l - - - futu re
observed
Runoff
forecast
.... -:- ),.~ ..... .
.-;..
' \ -. .
\
.
observed flood hydrograph
(at present still unknown)
' ... " ....
\ ••• - --- forecast hydrograph
, ..
,
t* = time of forecast
\, '''',
Fig. 16.2. The principle of flood forecasting in real-time on the basis of observed and forecast
rainfall