A very famous quote about
modeling “With poor assumptions, a man can make more mistakes with a computer
in a milli-second, than he could in a lifetime of common sense”. An assembly of
concepts in the form of a mathematical equation that portrays understanding of
a natural phenomenon is called model. Hydrologic models are simplified, conceptual representations of
the Hydrologic cycle.
Why Modeling is Required?
Modelling has become an integral part of the
decision making process for water engineers and managers. Recent
research in hydrologic modelling tries to have a more global approach to the
understanding of the behaviour of hydrologic systems to make better
predictions and to face the major challenges in water resources management
[Source: Training workshop on Hydrological Modelling by Hollings Foundation,
Recently, Hydrological models have taken over
the most important tasks in problem solving in hydrology (UNESCO, 1985). It is
valuable for studying potential impacts of changes in land use or climate. As
one report of CSDMS (Community Surface Dynamics Modelling System)56
Hydrological models are Present.
Types of Modelling
In science and
engineering, a black box is a device, system or object which can be viewed in terms of its inputs and
outputs (or transfer characteristics), without any knowledge of its internal workings. Its implementation
is “opaque” (black). Almost anything might be referred to as a black
box: a transistor, an algorithm, or the human brain.
A conceptual model
is a representation of a system, made of the composition of concepts which are
used to help people know, understand, or simulate a subject the model
represents. People receive information, process this information, and respond
accordingly many times each day. This sort of processing of information is
essentially a conceptual model (or mental model) of how things in our
surrounding environment work.
model is one that has an exact solution that relates the independent variables
of the model to each other and to the dependent variable. For a given set of
initial conditions, a deterministic model yields the same solution each and
Do not account for the spatial distribution of input variables or parameters. Do not require a digital elevation model (DEM) as
input. Also Known as “Low Rank”
Models. Ex- SRM (Snowmelt-Runoff
Model), WATBAL etc.
are partially varying in space by dividing the basin into sub basins.
It has two types:
Kinematic wave theory models
(KW models, such as HEC-HMS),
models (PD models, such as TOPMODEL).
SWAT is a semi-distributed physically based parameter model which is used
to simulate the ﬂow of very small to very large watershed not only in the US
but also in the whole world. SWAT can simulate the ﬂow process in a broad range
of watersheds. The SWAT hydrological model was established and has been used by
Hydro-Quebec for 20years. It is presently used for forecasting of inﬂows on all
ranges of the watershed. Studies showed that SWAT can work efﬁciently for the
simulation of hydrological studies. The following conclusions have been drawn,
which are also on the basis of previous studies:
(i) The efﬁciency of the SWAT model is very high for the hydrological
studies for the large catchment. (ii) Satisfactory simulation is obtained for
daily, monthly, seasonally and annual runoffs. (iii) The performance of the
snow-melting process of SWAT is satisfactory. (iv) Projection of stream ﬂows
under climate change is possible. (v) SWAT is in the public domain.
of Hydro-climatic modeling
Water is an essential
element for survival of living things. It is vital factor for economic
development and augmenting growth of agriculture and industry especially in the
perspective of rapidly increasing population and urbanization. Many zones face
scarcity of freshwater or subject to pollution. Thus, the availability and the sustainable
use of the water resources become the core of the local and national strategies
and politics in these regions. To deal with water management issues, one must
analyze and quantify the different elements of hydrologic processes taking
place within the area of interest. Obviously, this analysis must be carried out
on a watershed basis because all these processes are taking place within
individual micro watersheds. Hydrological processes and their local scattering
have always direct relation to weather, topography, geology, and land use of
watershed in addition to the impact of human activities. A watershed is
comprised of land areas and channels and may have lakes, ponds or other water
bodies. The flow of water on land areas occurs not only over the surface but
also below it in the unsaturated zone and further below in the saturated zone.
The use of a watershed model to simulate these processes plays a fundamental role in addressing a range of water resources and environmental and social problems. The development of remote sensing (RS) techniques and Geographic Information System (GIS) capabilities has encouraged and improved the expanded use of watershed models worldwide. GIS is a suitable tool for the efficient management of large and complex database and to provide a digital representation of watershed characteristics used in hydrologic modeling. It has added confidence in the accuracy of modeling by providing more practical approach toward the watershed conditions, defining watershed characteristics, improving the efficiency of the modeling process and ultimately increasing the estimation capabilities of hydrological modeling.
Salman Khan islecturer at Civil Engineering Department, Sarhad University, Peshawar.