Holman I.P.,Cranfield University |
Hess T.M.,Cranfield University |
Rose S.C.,JBA Consulting
Hydrological Processes | Year: 2011
Although the importance of sustainable soil management is recognized, there are many threats to soils including widespread soil structural degradation. This reduces infiltration through the soil surface and/or the percolation of water through the soil profile, with important consequences for crop yields, nutrient cycling and the hydrological response of catchments. This article describes a broad-scale modelling approach to assess the potential effect that improved agricultural soil management, through reduced soil structural degradation, may have on the baseflow index (BFI) of catchments across England and Wales. A daily soil-water balance model was used to simulate the indicative BFI of 45 696 thirty-year model runs for different combinations of soil type, soil/field condition, land cover class and climate which encapsulate the variability across England and Wales. The indicative BFI of catchments was then calculated by upscaling the results by spatial weighting. WaSim model outputs of indicative BFI were within the 95% confidence intervals of the national-average BFI values given for the Hydrology of Soil Type (HOST†) classes for 26 of the 28 classes. At the catchment scale, the concordance correlation coefficient between the BFI from the WaSim model outputs and those derived from HOST was 0·83. Plausible improvements in agricultural soil/field condition produced modest simulated increases of up to 10% in the indicative BFI in most catchments across England and Wales, although for much of southern and northern England the increases were less than 5%. The results suggest that improved soil management might partially mitigate the expected adverse effects of climate change on baseflow to rivers. Healthy, well-functioning soils produce many additional benefits such as better agricultural yields and reduced pollutant movement, so improved soil management should provide win-win opportunities for society, agricultural systems and the environment and provide resilience to some of the expected environmental impacts of climate change. © 2011 John Wiley & Sons, Ltd..
Neal J.,University of Bristol |
Keef C.,JBA Consulting |
Bates P.,University of Bristol |
Beven K.,Lancaster University |
Leedal D.,Lancaster University
Hydrological Processes | Year: 2013
Effective flood risk management depends on methods for estimating flood hazard and an appraisal of the dominant uncertainties in the analysis. Typically, hydraulic models are used to simulate the extent of flooding for an estimate of the flow in a particular reach for a chosen probability of exceedance. However, this definition causes problems at river confluences where flows derive from multiple sources. Here, a model-based approach was adopted to describe the multisite joint distribution of river flows for three rivers that converge on the city of Carlisle (UK). Monte-Carlo methods were used to generate flood events with realistic spatial dependence between tributaries which would occur over a 1000year period. To account for the uncertainty in the data used to create the event set, block bootstrapping was used to produce a further 100 runs of the event generator over notional 1000year periods. Each of the 20000 events created by this process was then simulated using a 10m resolution two-dimensional hydraulic model of the whole city to demonstrate the feasibility of the approach. Spatial dependence was found to be important because no single event caused the maximum flood extent at all locations and assuming perfect correlation between tributaries overestimated flood hazard. Uncertainty in estimates of inundation probability was significant to the extent that confidence intervals in risk estimates were larger than expected; however, the interaction of flows with the flood defences and valley topography gave a distinct structure to the inundation probabilities and risk. © 2012 John Wiley & Sons, Ltd.
Jeremy B.,JBA Consulting
Proceedings of the Institution of Civil Engineers: Forensic Engineering | Year: 2013
A review of accident reports and other sources has shown there have been 15 fatalities, and perhaps 4-5 times that number of injuries, which can be attributed to structural failure during flooding on the railway system in Britain since the 1840s. The resulting present-day economic damage is estimated to be at least £300 million. Bridge failure due to flooding is most commonly associated with 'extreme' but not necessarily 'very rare' floods; the average event rarity associated with catastrophic failure is 1 in 160-year return period, but the range of 200-250 years includes most floodrelated failures. Undermining of abutments and piers by scour is the most common form of failure of bridges. The remaining failures can be attributed to six other failure sequences which are currently not adequately addressed within the existing procedures. Of these six, debris collection resulting in enhanced local scour and the location of structures in rapidly responding catchments are considered the most significant. It is recommended that the design flood for scour assessment and protection design should be based on a 200-year return period flood event. A higher value (of 1000 years) may be appropriate for structures with a particularly high consequence of failure. © ICE Publishing: All rights reserved.
Forsythe N.,Northumbria University |
Fowler H.J.,Northumbria University |
Kilsby C.G.,Northumbria University |
Archer D.R.,JBA Consulting
Water Resources Management | Year: 2012
Now and in the future, the flows of the Upper Indus Basin (UIB) are and will be depended upon by hundreds of millions of people for their food security and economic livelihoods. Communities in the headwater reaches of the UIB-which contribute the bulk of runoff for the basin-are equally deserving of improved living conditions, but often lag behind downstream communities in benefitting from infrastructure. Harsh and highly variable climatic conditions pose specific challenges for local agricultural activities in the headwater reaches. Improved scientific understanding of tributary basin scale hydrology should support local development work as well as improvements to large scale infrastructure and water resource management. This study focuses on the challenge of providing meaningful quantitative information at the village/valley scale in the upper reaches of the UIB. The typology of the UIB hydrological regimes-as observed in large gauged basins-are examined, with special emphasis on annual cycles and interannual variability. Variations in river flows (as relative anomalies of discharge rates or runoff) are compared to observations of climate parameters (2 m air temperature, precipitation) from both local (point-based) observations and analogous parameters from remote sensing data products from the MODIS instrument. Although the temporal overlap is limited between river gauging data available to this study and the MODIS observational record, numerical analysis of relationships between relative anomalies in the spatial data and river gauging observations demonstrate promising potential of the former to serve as quantitative indicators of runoff anomalies. In order to translate these relationships to the scale of ungauged village/valley catchments, the available remotely sensed spatial data-snow covered area (SCA), land surface temperature derived (LST)-are assessed as analogues for meteorological point observations. The correlations between local (point-based) observations and remotely-sensed spatial data products are tested across a wide range of spatial aggregations. These spatial units range from the primary contributing area (nearly 200,000 km 2) of the UIB at its downstream gauging station Besham to a small valley serving a minor settlement (10 km 2). The shape and timing of annual cycles in SCA and LST are consistent across the range of spatial scales although the magnitudes of both intra-annual and interannual variability differ with both spatial scale and hydrological regime. The interannual variability exhibited by these spatial data products is then considered in terms of its potential implications for the smaller hydrological units. Opportunities for improvement and extension of this methodology are also discussed. © 2011 Springer Science+Business Media B.V.
Faulkner D.,JBA Consulting |
Keef C.,JBA Consulting |
Martin J.,Office of Public Works
Hydrology Research | Year: 2012
In setting design inflows to hydrodynamic models of flood flow along rivers, there can be a conflict between site-specific hydrological estimates of flow for a given return period and what the river model calculates as it routes flood hydrographs. This paper describes research carried out as part of the Flood Studies Update programme in Ireland, aimed at developing guidance on how to divide up river models and set the magnitude and timing of their inflows so that conditions in the model reach correspond to the expected design flood return period. A model for the joint distribution of flood peaks at pairs of catchments has been developed. The relationship between flood return periods is linked to physical differences between catchments. The model thus allows estimation of the statistical distribution of the flood return period expected at one site during a flood of specified return period elsewhere. A separate regression model predicts the relative timings of flood peaks on pairs of rivers. A summary of the resulting practitioner guidance is given, along with an overview of the testing of the method. The paper concludes with a discussion of the potential for application of the spatial dependence model to other problems in hydrology. © 2012 IWA Publishing.