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Integrated Modelling In The River Frome And Piddle Catchment And The Downstream Estuary Poole Harbour With Impacts From The Agricultural Activities

Congress: 2015
Author(s): JIE SHI (Cardiff, UK), Michaela Bray, Roger Falconer
Cardiff University1

Keyword(s): Sub-theme 3: Hydrology,
AbstractClimate change is expected to have a significant impact on flooding in the UK, inducing more intense and prolonged storms. Floods such as Boscastle 2004, Carlisle 2005, the summer Floods of 2007 and more recently in North Wales in June 2012 have been associated with unusual weather patterns. Such frequent flooding is already having an impact on catchment water quality. Flooding increases the quantity and transit time of contaminants and sediments entering the water course. Frequent flooding, due to climate change, will therefore exacerbate catchment water quality. Land use is also a contributing factor; For example, the move to more intensive farming could cause an increase in faecal coliforms, nitrates and other pollutants entering the water courses via catchment runoff. In an effort to understand better the effects on water quality from the combination of both land use and climate change, the hydrological and estuarine processes are being modelled using SWAT (Soil and Water Assessment Tool), linked to the Hydro-environmental Research Centre's 2-D DIVAST model (Falconer et al, 1999 ). The focus of the current work is centred on the transportation and decay of coliforms from agricultural runoff into the rivers Frome and Piddle in the UK. The nitrate concentrations and river flows are already modelled in a six years period between 1996 and 2001. By linking the 2-D DIVAST model with SWAT, it is possible to quantify how much of each pollutant reaches the harbour and the impact this has on water quality within the harbour. The other Welsh catchment will be undertaken which will incorporate the coupled SWAT-DIVAST model system. In undertaking these linkages refinements from parallel research, studies will also be made to the kinetics for coliforms and possibly nitrates in the hourly time step. The use of weather forecasting models linked to this integrated system will provide an added novel research element to this research focused on Dr Bray's expertise (Bray et al, 2010). The results show that the SWAT model setup at Frome and Piddle catchment is successful. The model calibration on the flow and faecal coliform reflects the model simulation in the watershed with relatively high accuracy. The Nash Suttcliffe value is between 0.7 and 0.9 in the model calibration and validation spatially. The project also looks into the sub daily model performance, which compared daily output and hourly output of flow and bacteria respectively. This comparison showed the coherency of the model simulations under daily and hour time steps. The hourly simulation estimated hourly flows that could catch up the flash flow and peak flow with high accuracy. The upstream catchment modelled showed that partial of faecal coliform contribution comes from the agricultural land with cattle, sheep and livestock. The DIVAST model showed the hydrometric and faecal coliform concentration from the estuary matches the observed measurement with high accuracy. In conclusion, the integrated modelling of SWAT and DIVAST is successful in the applications of model setup in the catchment and the downstream estuary with sound model performance. The catchment model showed the faecal coliform concentrations in the rivers are affected by the local farms i.e. agricultural activities. However, part of the faecal coliform enters the downstream water course in the estuary that might cause health problems to the people that using bathing water nearby. Therefore, to solve the problem an integrated plan is required to address the source of the bacteria contamination problem in the upstream rivers. 1. Falconer, R. A., Lin, B., Wu, Y. and Harris, E. L. 1999. DIVAST Model Reference Manual. Environmental Water Management Research Centre, Cardiff University, October, pp.33. 2. Bray M., Han D., Xuan Y., Bates P., & Williams M. 2010. Rainfall uncertainty for extreme events in NWP downscaling model, Hydrological Processes, ISSN: 0885-6087
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