Modelling runoff quantity and quality in tropical urban catchments using storm water management model

Due to differences in rainfall regimes and management practices, tropical urban catchments are expected to behave differently from temperate catchments in terms of pollutant sources and their transport mechanism. Storm Water Management Model (SWMM) was applied to simulate runoff quantity (peakflow and runoff depth) and quality (total suspended solids and total phosphorous) in residential, commercial and industrial catchments. For each catchment, the model was calibrated using 8-10 storm events and validated using seven new events. The model performance was evaluated based on the relative error, normalized objective function, Nash-Sutcliffe coefficient and 1:1 plots between the simulated and observed values. The calibration and validation results showed good agreement between simulated and measured data. Application of Storm Water Management Model for predicting runoff quantity has been improved by taking into account catchment's antecedent moisture condition. The impervious depression storages obtained for dry and wet conditions were 0. 8 and 0. 2 mm, respectively. The locally derived build-up and wash-off parameters were used for modelling runoff quality

Coping with climate variability and climate change in La Ceiba, Honduras

La Ceiba, Honduras, a city of about 200,000 people, lies along the Caribbean Sea, nestled against a mountain range and the Rio Cangrejal. The city faces three flooding risks: routine flooding of city streets due to the lack of a stormwater drainage system; occasional major flooding of the Rio Cangrejal, which flows through the city; and flooding from heavy rainfall events and storm surges associated with tropical cyclones. In this study, we applied a method developed for the U. S. Agency for International Development and then worked with stakeholders in La Ceiba to understand climate change risks and evaluate adaptation alternatives. We estimated the impacts of climate change on the current flooding risks and on efforts to mitigate the flooding problems. The climate change scenarios, which addressed sea level rise and flooding, were based on the Intergovernmental Panel on Climate Change estimates of sea level rise (Houghton et al. 2001) and published literature linking changes in temperature to more intense precipitation (Trenberth et al., Bull Am Meteorol Soc, 84:1205-1217, 2003) and hurricanes (Knutson and Tuleya, J Clim, 17:3477-3495, 2004). Using information from Trenberth et al., Bull Am Meteorol Soc, 84:1205-1217, (2003) and Knutson and Tuleya, J Clim, 17:3477-3495, 2004, we scaled intense precipitation and hurricane wind speed based on projected temperature increases. We estimated the volume of precipitation in intense events to increase by 2 to 4% in 2025 and by 6 to 14% by 2050. A 13% increase in intense precipitation, the high scenario for 2050, could increase peak 5-year flood flows by about 60%. Building an enhanced urban drainage system that could cope with the estimated increased flooding would cost one-third more than building a system to handle current climate conditions, but would avoid costlier reconstruction in the future. The flow of the Rio Cangrejal would increase by one-third from more intense hurricanes. The costs of raising levees to protect the population from increased risks from climate change would be about $1 million. The coast west of downtown La Ceiba is the most vulnerable to sea level rise and storm surges. It is relatively undeveloped, but is projected to have rapid development. Setbacks on coastal construction in that area may limit risks. The downtown coastline is also at risk and may need to be protected with groins and sand pumping. Stakeholders in La Ceiba concluded that addressing problems of urban drainage should be a top priority. They emphasized improved management of the Rio Cangrejal watershed and improved storm warnings to cope with risks from extreme precipitation and cyclones. Adoption of risk management principles and effective land use management could also help reduce risks from current climate and climate change. © 2011 Springer Science+Business Media B.V.Joel B. Smith, Kenneth M. Strzepek, Julio Cardini, Mario Castaneda, Julie Holland, Carlos Quiroz, Tom M. L. Wigley, Jose Herrero, Peter Hearne, John Furlo

Cascade impact of hurricane movement, storm tidal surge, sea level rise and precipitation variability on flood assessment in a coastal urban watershed

For comprehensive flood assessment, complex systems, both natural and man-made, must be accounted for due to prevailing cascade effects from the upper atmosphere to the subsurface with hydrological and hydraulic interactions in between. This study aims to demonstrate such cascade effects via an integrated nearshore oceanic and coastal watershed model. Such an integrated modeling system consists of a coupled hydrodynamic circulation and wave driven model [the ADvanced CIRCulation (ADCIRC) and Simulating WAves Nearshore (SWAN) models], which can combine storm surge, astronomic tide levels and wave interaction, as well as an integrated hydrological/hydraulic model, namely the Interconnected Channel and Pond Routing (ICPR) model for coastal urban watershed simulation. In order to explore the worst scenario of coastal flooding impacts on a low-lying coastal watershed, the Cross Bayou Watershed within the Tampa Bay area of Florida was chosen for a multi-scale simulation analysis. To assess hurricane-induced storm tide, precipitation variability, and sea level rise collectively this multi-scale simulation analysis combines ADCIRC/SWAN and ICPR integratively. Findings indicate that such consideration of complex interactions at the coastal ocean, land surface, and sub-surface levels can provide useful flood assessments which are sensitive to slight changes in natural hazard characteristics such as storm intensity, radius of maximum winds, storm track, and landfall location