Off-Stream Detention Design for Storm-Water Management
AbstractA detention basin is designed for storm-water quantity and quality controls. An in-stream basin is often located on a widened floodplain, whereas an off-stream basin can be part of open space in a parking lot, park, or sport field. The inflow channel associated with an off-stream basin is allowed to carry its base flow not to exceed the downstream capacity. When the inflow channel is full, the excess flood water is diverted into the off-stream basin through the side weir. During the flood recession, the equalizer conduit drains the basin flow back to the channel. In this study, the rational volumetric method was expanded from in-stream to off-stream detention design. The required off-stream detention volume is maximized by the rainfall event longer than the time of concentration of the tributary area. In comparison, the off-stream detention volume can be significantly less than an in-stream, depending on the flow-through capacity in the downstream channel. This paper presents a design procedure to...
HYDROLOGIC MODELING OF DETENTION POND
Urban watersheds produce an instantaneous response to rainfall. That results in stormwater runoff in e xcess of the capacity of drainage systems. The excess stormwater must be man aged to prevent flooding and erosion of streams. Ma nagement can be achieved with the help of structural stormwater Best Managem ent Practices (BMPs). Detention ponds is one such B MP commonly found in the Austin, TX, USA. The City of Austin developed a pla n to mitigate future events of flooding and erosion , resulting in the development and integration of stormwater BMP algorithms into t he sub-hourly version of SWAT model. This paper dea ls with the development of a physically based algorithm for detention pond. Th e algorithm was tested using a previously flow-cali brated watershed in the Austin area. From the test results obtained it appears tha t the detention pond algorithm is functioning satis factorily. The algorithm developed could be used a) to evaluate the function ality of individual detention pond b) to analyze th e benefits of such structures at watershed or higher scales and c) as design tool.
Impacts of climate and land use changes on flood risk management for the Schijn River, Belgium
Abstract Flooding is the most common natural disaster in Europe. Modern flood risk management relies not only infrastructure development but also on governmental and non-governmental actors applying legal, economic and communicative water management instruments. Within the European Union (EU), flood management closely relies on policy set at the EU and national levels. It is now recognized that a sound understanding of climate change is required in addition to current management by taking into account land use change and socio-political context, as climate and land use changes have major impacts on hydrological responses. This paper investigates the hydrological behavior due to urbanization under current and future climate scenarios of high summer and high winter rainfall for 20 sub-catchments of the Schijn River, located in the Flanders region near Antwerp, Belgium. As urbanization increases and existing rainfall-runoff models neglecting the specific behavior of urban runoff, a hydrological model was developed based on a basic reservoir concept and applied to the existing rainfall-runoff model (PDM) flow to examine the specific urban contribution. Results revealed that peak flow for urban runoff and the total peak flow (i.e. rural and urban runoff) were significantly higher (i.e. ranges from 200% to 500%) than the existing rainfall-runoff model (PDM) flows, because of faster and more peaked urban runoff response. The impact of climate change on current and future conditions was also assessed by estimating peak flows with respect to return periods from the flood frequency curve. The predicted peak flow of high summer future climate scenario was significantly higher (i.e. ranges from 200% to 250%) than that of the current climatic condition for this region. Furthermore, hourly peak flow and daily volume ratios of 100-year return period for the highest, lowest and average impervious area were projected for the time horizon of the year 2100. It is concluded that climate change impacts contribute the most in producing peak flow in coming years, while increased urbanization takes the second place for both hourly and daily values. Results on urbanization effect and climate change impact assessment are useful to the water managers for spatial planning, emergency planning and insurance industry.