Integrated management of river basins
Practical work 2
Integrated modelling of a watershed. Sensitivity testing to
management practices (land use and point discharges).
IST, academic year 2014/15
Context
Integrated watershed management requires the use of integrative
tools able to describe the functioning of the basin in the current
situation and to assess the impact arising from changes due to
management measures or to inter-annual climate variability or as
a result of changes in the climate itself (so-called climate change).
These tools need predictive capacity and therefore have to be
based on models. Deterministic models are based on the
simulation of physical and biogeochemical processes and are
therefore the most convenient to make predictions of evolution
due to profound changes that modify the basin sufficiently to
withdraw the data values measured before this change.
The watershed has spatial variability due to a panoply of reasons,
which include topographical characteristics, soil properties and
land use, geology and climate, whose exhaustive description is
impossible, whether by lack of information or inability to process
information. As a consequence the deterministic models also rely
on statistical information for its implementation. The amount of
empirical information increases together with the simplicity of
basin processes representation.
Basin models are usually grouped into 3 broad categories, of
increasing complexity: (1) integral models, (2) semi-distributed
models and (3) distributed models. Integral models aim to
describe the quantity and quality of water at the basin (or subbasin) discharge point. Semi-distributed models divide the basin
in sub-basins of more or less homogeneous characteristics and
analyze them separately, being the properties at the point of
discharge the result of the sum of the contributions of the various
sub-basins. Distributed models use a mesh to describe the basin
and solve fundamental equations using this mesh.
The models distributed are pedagogically most interesting
because explicitly integrate the knowledge acquired by students in
basic disciplines where are presented the knowledge of physics,
biology and chemistry involved in the processes that determine
the functioning of the watersheds.
Purpose of the job
The work aims to implement a general basin model and create
sensitivity to the potential for their use and for the causes of
uncertainty associated with the results and how to overcome
them.
The specific objectives are:
 Analyze the model implementation process,
 Analyze the consequences of land use change.
Easily could tests be made to the parameters of the model, soil
properties, climate, agricultural practices or point discharges, but
the time available did not permit it.
Methodology
The work will be based on the model MOHID Land and uses
knowledge gained in the discipline of Environmental Modeling.
In this subject students have acquired knowledge of numerical
methods, biogeochemical processes and modeling of transport
processes and made a MOHID Water model application in an
estuary using the graphical user interface MOHID Studio, which
is common to models MOHID Land and MOHID Water.
In this discipline the case study will be the Sorraia River basin
where the model is applied using a mesh with step of spatial 500
meters to describe the basin and a one-dimensional network to
describe the hydrographic network.
The sensitivity studies referred above shall be carried out by
changing the data files. Each simulation must consume a couple
of hours of CPU on a computer medium.
Structure of the report
The report shall present maps with basin basic data (topography,
hydrographic network, soil and land use) and climate data (annual
average rainfall and temperatures). The results should be
presented in the form in which the interface of the model
produces them in order to save effort.
The report must include comparison of river discharge time series
in both scenarios and a time series of nitrate (if the simulation was
possible in student’s computers). Examples of spatial distributions
of soil moisture and nitrate for one day (or contrasting days, e.g.
raining and dry seasons).
The time series at the point of discharge of the basin should be
presented for the two scenarios of land use. It is suggested that the
second scenario situation is the pristine basin condition admitting
that in this situation, the soil is covered with forest.
Calendar
The implementation of the model will be made during the lectures
and the report shall be delivered no later than November 16.
Simulations carried out
Students must simulate the present situation and a second land use
scenario (e.g. pristine situation). Water quality simulations can be
performed for a short period (e.g. one month) because of
computing power limitations. Results of a longer simulation will
be provided to the students for their analyses.
Simulations with point sources discharged directly into the River
would be easily performed but are not mandatory, again for a
matter of time.