Methodology
Two approaches were considered to
assess this problem: a physically based approach and a statistical
approach.
Physical based model
The initial premise of the physically based approach was to develop a
model that could simulate the fluctuations in the water level using an
inflow peak hydrograph and remotely-sensed morphological characteristics
of the lake as inputs. It is known from compensating reservoir modelling
that lakes and reservoirs usually have an attenuation effect on the
inflow hydrograph, causing a reduction of the peak discharge value and a
release of the water volume during a longer period (United States
National Resources Conservation Service, National Engineering Handbook.
Section 630, Hydrology. Chapter 17, Flood Routing April 2014). The scale
of the attenuation depends on the characteristics of the lake or
reservoir, such as its storage capacity and the geometry of the spillway
(Gioia 2016). To simulate this behaviour, it is possible to proceed with
what is called flood routing, using as inputs the inflow discharge, the
volume of water retained in the lake and a relationship between the
variation of the water level and the outflow discharge.
A water balance equation is used to link the increase in the surface
water elevation to the difference between the volume entering the lake
and the volume leaving it at each time step.