Urban Drainage Planning Research Articles

Climate-resilient urban drainage planning: An approach using a GIS-based SCS-CN model

ABSTRACT Inexorable urbanization continues apace across the world and urban flooding in megacities is now frequently evidenced due to extreme rainfall events due to climate change (CC). Climate-resilient urban drainage planning is critical towards making sustainable cities or any new urbanization. This paper presents an approach through an insightful assessment of climate resilient urban drainage applying GIS-based Soil Conservation Service-Curve Number (SCS-CN) model of a new urban growth of megacity Dhaka, Bangladesh. A precise DEM (Digital Elevation Model) of the study area has been used for catchment delineation using ArcSWAT. Localized climate anomalies of rainfall of around 11% have been identified during monsoon from statistical downscaling and included in the cumulative rainfall event of 5 days. The effect of historical and CC-induced rainfall have been used to identify and map the peak discharges of sub-catchments considering the return period of 5-day cumulative rainfall for 10, 25, and 100 years of the urban catchment for both existing and future land-use scenarios accounting for the change in CN. The varying results of the peak discharges of the sub-catchments for resilient drainage planning is not only dependent on the increase in rainfall but also the combined response of the land-use and soil profile.

Toward Sustainable Urban Drainage Planning? Geospatial Assessment of Urban Vegetation Density under Socioeconomic Factors for Quito, Ecuador

Natural or anthropogenic urban vegetation is an important resource for urban planning, risk assessment, and sustainable development of a city. Quito is a megadiverse city due to its location and topography, but the socioeconomic diversity generates more contrasting conditions of certain behaviors and habits related to urban infrastructure. The contrasts of vegetation and green spaces in the different sectors of Quito also reflect the diversity of the city. This study examines the effects of socioeconomic conditions on the loss or increase of urban vegetation. The exploratory regression method (spatial) and logit model (non-spatial) were used to explain the socioeconomic effects on urban vegetation density at the level of urban parishes. On the one hand, the Normalized Difference Vegetation Index (NDVI) was calculated as the dependent variable based on the 2021 sentinel images. On the other hand, the independent variables were structured based on the socioeconomic level, the land valuation areas of Quito (AIVAS), and the quality of life index. This article contributes to establishing baseline information that helps structure the conditions, strategies, and investments to design and implement plans and programs for urban drainage, ecosystem benefits, and sustainable development in the city of Quito.

Socio-Economic Assessment of Green Infrastructure for Climate Change Adaptation in the Context of Urban Drainage Planning

Green infrastructure (GI) contributes to improve urban drainage and also has other societal and environmental benefits that grey infrastructure usually does not have. Economic assessment for urban drainage planning and decision making often focuses on flood criteria. This study presents an economic assessment of GI based on a conventional cost-benefit analysis (CBA) that includes several benefits related to urban drainage (floods, combined sewer overflows and waste water treatment), environmental impacts (receiving water bodies) and additional societal and environmental benefits associated with GI (air quality improvements, aesthetic values, etc.). Benefits from flood damage reduction are monetized based on the widely used concept of Expected Annual Damage (EAD) that was calculated using a 1D/2D urban drainage model together with design storms and a damage model based on tailored flood depth–damage curves. Benefits from Combined Sewer Overflows (CSO) damage reduction were monetized using a 1D urban drainage model with continuous rainfall simulations and prices per cubic meter of spilled combined sewage water estimated from literature; other societal benefits were estimated using unit prices also estimated from literature. This economic assessment was applied to two different case studies: the Spanish cities of Barcelona and Badalona. The results are useful for decision making and also underline the relevancy of including not only flood damages in CBA of GI.

A Simple Method to Develop a Formula for Estimating Concentration Time of Drainage Design

Concentration time of rainfall is an important aspect to determine drainage design. A general rational formula is used to determine design flood or peak flow in urban drainage planning, especially for storm sewer design. The use of this balanced formula requires rainfall intensity, whose duration of rain is equal or more than the time of concentration. This time of concentration is determined using an estimation formula whose formation requires measurement data of the time of concentration. This study introduces how to measure the time of concentration using the concept of-rational-hydrograph, in which peak flow occurs at the time of concentration. To fulfill the aim of this research, an experimental of catchment area planted with Zoysia Japonica grass and showered with a rainfall simulator was conducted. The length of the flow path on the land, L, given in 5 variations, namely 50 cm, 100 cm, 150 cm, 200 cm, and 250 cm, was used. The slope of the land, S, is given in 3 variations, namely 2.8 %, 5,6%, and 8.8%. For each variation of L and S, the experimental catchment area was poured with a fixed rainfall intensity, which is 60 mm/hour. The flow was measured every 5 minutes intervals. Then, from the relationship of flow and time, a rational hydrograph was formed, from which the time of concentration, Tc, was deduced. This Tc value was treated as the measured Tc to form the Tc estimation formula using the regression formula. The formula is Tc = 3.543 + 1.211 L – 17.119 S, with the coefficient of determination R2 = 0.98. These results show that the determination of Tc using the concept of the rational- hydrograph is acceptable. This formula applies to L and S values greater than zero and applies to land covered by Zoysia Japonica grass. Further research is needed for other types of land cover to validate the formula obtained in this research.

Up-to-date urban rainstorm intensity formulas considering spatial diversity in China

With accelerating urbanization in China, urban waterlogging has had a serious impact on urban sustainable development and citizen welfare. Simple urban rainstorm intensity formulas with a monotonous frequency distribution type cannot meet the practical needs of urban drainage planning and design. This study focuses on the development of urban rainstorm intensity formulas based on spatial diversity in China. Using the annual maximum sampling method, rainstorm data of 607 cities throughout China were collected into a database, with a total of 24,933 rainfall samples (annual observations) under various specified precipitation durations. The database was used to verify that integrating the Pearson III and Gumbel distributions would constitute an optimal theoretical distribution type, owing to its small error and increased fitting precision. Modification and coordination of four important parameters in the rainstorm intensity formula were done using a digital elevation model, which improved the accuracy of the formula. In addition, precipitation distributions in China were treated from the perspective of topographic features to validate the calculations from up-to-date formulas. Accuracy assessment was accomplished using a national code (GB-50014-2006), GIS-based isograms, and authoritative results from the Hydrological Bureau of the Ministry of Water Resources. This work provides a comprehensive foundation for the establishment of an up-to-date rainstorm intensity formula for China, which can be used widely in different cities.

Storm Water Runoff and Deep Groundwater Drainage in Two Closed Basins

Closed basins dotting the landscape of south and central Florida have aroused the interest of numerous hydrologists in the past. Lacking surface water drainage features such as creeks and natural streams, closed basins drain internally through the subsurface during storm events. Little is known, however, about the magnitude and role of subsurface drainage fluxes to deep groundwater aquifers. In this study, instruments were deployed to monitor the surficial and deep aquifer heads at groundwater discharge points in two urbanized closed basins. The purpose of the study was to develop and apply field methods to estimate rapid subsurface runoff following rainfall events and evaluate the effectiveness of internal drainage in urban drainage planning. The two sites were in Hillsborough County, Florida, and one location was a 6-m-deep sinkhole that receives urban runoff from the rest of the basin. The data captured rapid subsurface drainage exceeding 25 cm/day at these discharge locations following rainfall. The two locations collected subsurface runoff rapidly and released the runoff gradually into the deep aquifer system. Results have practical implications for urban drainage in closed basins.

Modelling urban river catchment: a case study in Malaysia

Generally, many rivers within urban catchments in Malaysia are being altered from their natural states to meet the demand of developments. Most of these rivers have also become the receiving water body for urban drainage systems. Therefore, it has become extremely difficult to separate river from the rest of the drainage system. Study of interaction between such river and urban drainage is necessary for urban drainage planning and design. Present study showcases how urban river modelling using InfoWorks Collection System (CS) on Berop River, Perak (Malaysia), can assist stormwater system design. Calibrated using historical flood event, the developed model was used for evaluation of various design storms, possible scenarios as well as existing and future landuse condition. The study found that within a data scarcity condition, InfoWorks CS played a significant role in providing good platform for stormwater system modelling as well as satisfactory simulations and analyses for complex combination of river and urban drainage stormwater system. This is the much needed advantage for practising engineers in time saving stormwater system design.

Hydrodynamic Water Quality Simulation - An Approximative Solution

Impacts from combined sewer systems on receiving waters are heavily polluting a lot of small river ecosystems. A simulation model which can be used to predict the development of water quality after combined sewer overflows and other impacts from the urban drainage system has been developed. This model works with hydrodynamic flow calculation because it is applied in a system of small wetland creeks with nonstationary flow conditions. The numerical solution of the differential equations is described as well as calibration results. It is shown that water quality simulation based on the one-dimensional mass transport equation is possible for nonstationary flow conditions and is going to become very useful in urban drainage planning.

Stormwater Management Measures in Ontario: Status and Problems in Implementation

Results of a survey of Ontario municipalities indicate that a majority are utilizing stormwater management (SWM). The use of SWM is more common either among large and/or rapidly growing municipalities. Of those municipalities employing a traditional approach to urban drainage planning and design, most perceive a need for the adoption of SWM measures. The main problems encountered in instituting SWM were related to an initial lack of understanding on the part of land developers and inadequate funding.