Contribution of directly connected and isolated impervious areas to urban drainage network hydrographs

Abstract

Abstract. This paper addresses the mass balance error observed in runoff hydrographs in urban watersheds by introducing assumptions regarding the contribution of infiltrated rainfall from pervious areas and isolated impervious area (IIA) to the runoff hydrograph. Rainfall infiltrating into pervious areas has been assumed not to contribute to the runoff hydrograph until Hortonian excess rainfall occurs. However, mass balance analysis in an urban watershed indicates that rainfall infiltrated to pervious areas can contribute directly to the runoff hydrograph, thereby offering an explanation for the long hydrograph tail commonly observed in runoff from urban storm sewers. In this study, a hydrologic analysis based on the width function is introduced, with two types of width functions obtained from both pervious and impervious areas, respectively. The width function can be regarded as the direct interpretation of the network response. These two width functions are derived to obtain distinct response functions for directly connected impervious areas (DCIA), IIA, and pervious areas. The results show significant improvement in the estimation of runoff hydrographs and suggest the need to consider the flow contribution from pervious areas to the runoff hydrograph. It also implies that additional contribution from flow paths through joints and cracks in sewer pipes needs to be taken into account to improve the estimation of runoff hydrographs in urban catchments.

Impacts of urbanisation on hydrological and water quality dynamics, and urban water management: a review

“…Furthermore, in pervious urban landscapes, hydrological connectivity to impervious areas is important in two senses: (1) runoff from impervious zones that passes over pervious land can rapidly increase the rate of saturation and result in quick attenuation of flows; and (2) saturationderived flows that are adjacent to impervious areas have pathways of low resistance that can facilitate rapid transfer of large volumes of water. The role of these zones on overall water balance is uncertain and the subject of continued research, but such dynamics may have a significant impact on small-scale proliferation of stormwater and resultant local flood risk (Seo et al 2013). …”

Concentrations and Loads of Dissolved and Particulate Organic Carbon in Urban Stormwater Runoff

“…In general, pervious surfaces (grass and tree canopy) play an important role in reducing the amount of stormwater runoff; however, once the soil in the catchment reaches saturation, the rainfall water flows horizontally across the land surface. This is an indicator that rainfall has exceeded the soil infiltration capacity, which then will lead to runoff [29]. Further, the pervious areas can be a major contributor to the variability in the runoff hydrograph and are the main cause for long hydrograph tails in urban environments [29].…”

“…This is an indicator that rainfall has exceeded the soil infiltration capacity, which then will lead to runoff [29]. Further, the pervious areas can be a major contributor to the variability in the runoff hydrograph and are the main cause for long hydrograph tails in urban environments [29]. Initially, it takes a longer time for pervious areas to become fully saturated, and only then runoff occurs.…”

“…Stormwater runoff flows slowly through rough surfaces, including turfgrass, and this is why pervious areas increase lag time and decrease high peak discharge, as well as steep rising and falling limbs. Surface runoff in pervious areas is more challenging to predict, as it is dependent on soil, site, and vegetation [29]. Wetzel et al [3] suggest that an OC first-flush likely occurs in urban areas, especially during initial rainfall following a prolonged dry period.…”

Improved hydrological modelling of urban catchments using runoff coefficients

“…For an individual building, road or car park it is possible to measure the proportion of the precipitation that lands on impervious areas which enters the sewer network (Lee and Heaney, 2003). However, the patchwork of green and built-up areas complicates analyses when considering the larger scale (Alberti et al, 2007;Seo et al, 2013).…”