An assessment of the impact of floodplain woodland on flood flows

This paper examines the potential role of floodplain woodland in flood alleviation. In theory, the presence of trees and associated woody debris on the floodplain increases the hydraulic roughness, thus slowing down flood flows and enhancing flood storage. One and two‐dimensional models were used to simulate a 2.2 km reach of river in south‐west England to test this theory for a 1 in 100 year flood using appropriate roughness parameters. Both models predicted a reduction in water velocity within the woodland, increasing water level by up to 270 mm and creating a backwater effect that extended nearly 400 m upstream. Flood storage increased by 15 and 71%, while flood peak travel time was increased by 30 and 140 min for the two scenarios simulated. The results suggest that there is considerable scope for using strategically placed floodplain woodland to alleviate downstream flooding. In particular, it offers a means of tackling the increased flood risk associated with climate change.     

Methodology and base cost models to determine the total benefits of preservation interventions on road sections in Switzerland

In Switzerland, it is common practice to estimate the total benefits of new roads before they have been built and of road improvement interventions before they have been performed. The guidelines with respect to standardised methodologies and models to be used have been developed (VSS 2003a VSS. 2003a. SN 641 820: Cost-benefit analysis in road traffic, Switzerland: Swiss Association of Road and Traffic Experts (VSS). Technical Committee 2: Planning and Development (in German) [Google Scholar]) and are now in use. It is not yet, however, common practice to estimate the total benefits of road preservation interventions and hence guidelines do not exist with respect to standardised methodologies and models to be used. In order to provide this information, the research package VSS 2004/710-716 was started. This paper presents the methodology and models proposed to be used to evaluate the total benefits of road preservation interventions in Switzerland based on the evaluation and synthesis of existing national and international literature on the relationships between pavement condition and benefits of road use conducted in project 714 of the research package. The use of the methodology and models are demonstrated by determining the optimal intervention strategy for a representative situation in Switzerland. The impact on the optimal intervention strategy of the consideration of multiple stakeholders is investigated.