The impact of peat on the discharge of the river Suck (Ireland); a hydrological modelling approach

Abstract

In 2009 the peatland river Suck in Ireland flooded with the highest discharge ever measured. The expected increase of precipitation due to climatic changes could lead to more severe flooding in the future. The influence of peat on the hydrology of the river Suck is difficult to quantify, as well for the many other peatland rivers on the Northern Hemisphere. The effects of peat bog excavation and human inference in peatland areas in general is unclear, though expectations are that excavations could enhance flooding. Therefore an attempt is made in this thesis to quantify the effects of peat bogs on the discharge of a river and how peat bog excavations affect the hydrology in the catchment. First of all a fieldwork was executed to map the subsurface of the catchment to obtain data on the subsurface. A detailed genesis of the catchment was obtained as well with this fieldwork. Samples were tested in the laboratory to provide a reference value of hydrological parameters, like hydraulic conductivity and porosity, for different facies in the research area. The entire catchment was modelled with a 100 by 100 meters resolution adjusted PCR-GLOBWB hydrological model with two different scenarios. A schematization was made for the present situation together with a scenario where half of the volume of peat is excavated in the future. The schematization of the present situation performed reasonably well and was able to show the seasonal and short term fluctuations of the river Suck within a magnitude that was near the measured values. The scenario with enhanced excavations resulted in two different responses: 1) The average discharge increased significantly, mainly as a result of a higher minimum discharge. 2) The maximum discharge decreased for an excavated peat scenario. However, problems in parameterization of hydraulic conductivity for peat and limitations of the model led to a misrepresentation of hydrological behaviour of peat for especially higher discharges, making the trends for the higher discharges less secure. From the reference values and the parameterization it became clear that peat plays an important role in the hydrological processes in the catchment by acting as a buffer and water storage. It is therefore quite safe to predict a higher average discharge and most likely a higher maximum discharge in rivers after peat bog excavation based upon the behaviour of the model combined with the reference values of hydraulic parameters from peat.