The impact of upland land management on flooding: insights from a multiscale experimental and modelling programme

Abstract

A programme of field experiments at the Pontbren catchment in Wales has, since autumn 2004, been examining the effects of land use change on flooding. The Pontbren catchment possesses a long history of artificial drainage of its clay soils and intensification of sheep farming. Increased flood runoff has been noted within the last decades, as has the mitigating effect of trees at field scale. To examine the local and catchment‐scale effects of land management within the catchment, including the potential advantages of planting additional trees, a multidimensional physically based model has been developed and conditioned on data from an intensely instrumented hillslope. The model is used to examine the effects of planting a small strip of trees within a hillslope. Results demonstrate that careful placement of such interventions can reduce magnitudes of flood peaks by 40% at the field scale. The challenges associated with upscaling these results to the Pontbren and Upper Severn catchments are discussed.

Catchment scale hydrological modelling: A review of model types, calibration approaches and uncertainty analysis methods in the context of recent developments in technology and applications

“…While statistical methods have been able to identify catchmentscale effects of urbanisation (e.g. Institute of Hydrology (1999)), most of the knowledge on the effect of land use change on hydrological response comes from experimental catchment studies, and hydrological modelling (see among others Jackson et al, 2008); however, different results have been obtained, with some even opposing the findings of the others .…”

Rural land management impacts on catchment scale flood risk

“…Overgrazing is the cause of 23% of soil degradation in Europe (Royal Society for Nature Conservation, 1996). A recent study at Pontbren (Jackson et al, 2008a;Marshall et al, 2009) found that small tree strips on hillslopes have the potential to reduce peak flows by 40%, as the land is no longer trampled by livestock. Figure 2.5 demonstrates the impacts of heavy grazing on the soil structure and the hydrological cycle.…”

“…Evans (1996) found that a 50% increase in stock numbers coincided with a 25% increase in surface runoff in the Derwent catchment between 1944 and 1975. A modelling study by Jackson et al, (2008a) found that introducing tree shelterbelts with no grazing decreased overland flow by up to 60%, resulting in peak flows decreasing by between 10% and 40%. Another key hydrological storage zone is water on the floodplain and slopes.…”

“…Jackson et al (2006; have used data to inform their modelling approach. This thesis has taken a different approach to the scaling problem, using data to downscale the downstream flood magnitude to the upstream contributing sub-catchments.…”

“…Furthermore, as the area decreases, the complexity of the model can be reduced, with fewer process included, and fewer uncertain parameters. Thus, as per Jackson et al (2006; 2008b) the focus of this research is use of a physically based model, to maintain a strong link to hydrological processes. This makes it easier to test land use scenarios with the model, as changes can be represented by changing physically meaningful parameters and land covers.…”