University of Twente Student Theses


Water Source Allocation and Numerical Water Quality Modelling in Roxo Reservoir Catchment, Portugal

Madamombe, Chenai Epiphania (2010) Water Source Allocation and Numerical Water Quality Modelling in Roxo Reservoir Catchment, Portugal.

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Abstract:This research focuses on the water source allocation in streamflow components of the Roxo catchment utilising two tools. The objective of which is to determine their applicability in understanding hydrological processes and water source partitioning in a mesoscale semi arid catchment. Firstly a stable isotope analysis framework and a two source mixing model are utilised. Secondly the results of RAM component of the DUFLOW Modelling Studio (DMS) simulation are used. Stable water isotopes because of their fractionation, abundance and conservative nature, are able to preserve the characteristics of the hydrological cycle even in mesoscale catchments. They are able to give an insight into the intrinsic processes and a physical representation of the physical processes within a hydrological system. This is an element that has not yet been addressed in previous studies in the Roxo catchment. Moreover the RAM component of the DMS model has not been used for source allocation. This combination is a first step towards determination of a way to eventually parameterise and calibrate the RAM model for the catchment. The isotope results show that there is an exterior recharge source to the water streams to those that are presumed present in the northern Pisoes subcatchment. The isotope determined contribution to the Roxo Reservoir inflow point at A28 in the southern sub-catchments from precipitation and groundwater were 43% and 57% respectively. The most contributing source in the different subcatchments is groundwater where contribution ranges 57-73% from the dry to wet season. Major hydrological process determined in the catchment was very high evaporation in the Roxo reservoir, the southern streams and open groundwater wells and mixing of different water discharges in the northern subcatchment around A23, A24, and A25 in stream network. Precipitation effects are overweighed by evaporation processes and mixing in the reservoir brings an almost uniform isotopic composition. The identified fault escarpment (Gabbros of Beja Aquifer System) in the northern subcatchments is attributed to the effect on streams in the region due to its inflows that have stronger effect than the evaporation and precipitation taking place. The isotopic two source mixing model proved too simple to describe some source contributions from northern subcatchments and mixing processes in the Roxo Reservoir as it omitted fractionation processes. Therefore a multiple source mixing model needs to be used in isotopic analysis. RAM DMS a numerical model simulates the rainfall runoff discharge based on surface and weather forces and Meteosat MSG-MPE precipitation data. The contribution from groundwater discharge was calculated to be highest (87%) compared to other streamflows, which agrees in order of magnitude with that determined through isotopic method. However much more RAM model parameterisation needs to be done and refinements made in order to be able to distinguish the sub processes in the different sub catchments. It was possible to estimate the portion for water discharge that emanated from surface runoff, groundwater and subsurface runoff from the different surfaces. In the southern part of the Roxo catchment, the contribution due to runoff (2%) is less than in the northern part (7%). This is not derived by the isotopes so a combined system is more useful. Future research should use an increased number of sample points for isotope data collection and could also incorporate remote sensing data for the estimation of parameters such as evapotranspiration and soil moisture. Combined with a further refined DMS numerical modelling it is will be possible to ii determine the exact source areas using the stable water isotope compositions as the signature of the water sources. Uncertainty estimation of both models used should also be carried out in further research. Key words: source allocation, stable water isotopes, water balance processes, RAM DMS model
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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