Morphological sustainability of barrage impoundments

Beevers, Lindsay C. (2003) Morphological sustainability of barrage impoundments. PhD thesis, University of Glasgow.

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Barrages built in estuaries fundamentally alter the dynamics of the river with regard
to both flow and sedimentation patterns. Therefore it is essential to ensure that these
structures do not affect the sustainability of the systems in which they are built. In
recent years there has been increased emphasis on assessing the effect of climate
change on river flows and the impact that this has on watercourses. Therefore, to
investigate morphological sustainability of barrage impoundments, the effect of
climate change must be included.
An assessment of the morphological sustainability of the River Tees impoundment is
presented. The predictions were completed using the l-dimensional software
package ISIS, which modelled flow and sediment movement within the
impoundment. Fifty-year simulations were completed to predict the sediment
distribution through the system under differing future scenarios.
A method is proposed for extending the flow boundary for the numerical model,
which uses a generic statistical modelling technique. It uses the historical flow data
recorded on the Tees and forward predicts the series based on its statistical
properties. Firstly, the Markov Chain method was used to predict a 50 year flow
series which assumes a stable climate. The predicted series showed good correlation
with the measured series in terms of both statistical properties and structure.
Secondly, the method was further developed to enable climate change predictions to
be incorporated. This means that the generated series can be modified to directly
account for the possible influence of climate change on discharge. This technique
uses a Markov model fitted in the framework of a multinomiallogit model, enabling
catchment precipitation and temperature values to be linked to the discharge.
Climate change predictions available for the period 2070 to 2100 were then used to
create 50-year modified flow series for the River Tees under a medium\high and
medium\low emissions scenario.

During the period of sediment monitoring on the Tees a change to the sediment
supply was noticed as a result of the high flows experienced in October/November
2000. Unfortunately, it is unclear whether the sediment supply will return to its
original levels or if, as a consequence of higher flows resulting from climate change,
the supply will remain at present levels. Hence three different sediment rating
curves were created from the field data to deal with this uncertainty; representing
high, medium and low sediment supply conditions.
Using the data generated for the flow and sediment boundaries, simulations were
undertaken to assess the morphological sustainability of the Tees impoundment.
Simulations using a flow boundary, which assumed both a stable climate and a
changed climate, as well as three different sediment supply options for each, were
considered. The results show that the impoundment reaches a dynamic equilibrium
during the modelled period, irrespective of the sediment supply. From this it is
possible to state that the Tees Impoundment is morphologically sustainable over the
next 50-80 years. Climate change, while increasing the sediment supply, actually
appears to improve the sustainability of the impoundment with regards to sediment.
The increased number of high flows cause more steep water surface slopes which reentrain
sediments and partially flush the system.

In conclusion this thesis presents an assessment of the morphological sustainability
of the Tees impoundment under differing future climate scenarios for both the fluvial
and sediment inputs. Within the course of the work a different technique for
extending flow series assuming both a stable and changed climate has been proposed.
It is hoped that these methods will be of use in future sustainability assessments;
however further investigations into these methods would be beneficial.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Colleges/Schools: College of Science and Engineering > School of Engineering
Supervisor's Name: Pender, Prof. Gareth and Sloan, Dr. William
Date of Award: 2003
Depositing User: Miss Louise Annan
Unique ID: glathesis:2003-4940
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 07 Feb 2014 15:12
Last Modified: 07 Feb 2014 15:41

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