Experimental study of water fluxes in a residential area: 2. Road infiltration, runoff and evaporation

Abstract

Abstract:Lack of accurate data has led some hydrologists and city planners to assume that urban infiltration is zero and runoff is 100% of the rainfall. These assumptions lead to an over estimation of road runoff volume and an underestimation of direct recharge to groundwater, which is already rising under some UK cities. This study investigates infiltration and runoff processes and quantifies the percentage of rainfall that contributes to storm drainage, and that which infiltrates through different types of road surface. Access tubes were installed for measuring soil water content using a neutron probe in three car parks, a road and a grass site at the Centre for Ecology and Hydrology, Crowmarsh Gifford, Wallingford. Storm drainage was recorded at the exit of the Thamesmead Estate in Crowmarsh Gifford, just before the drain joins the River Thames at Wallingford. Rainfall and water table depth were also recorded. Weekly measurements of soil moisture content indicated that the top 40 cm layer is not influenced by water-table fluctuations and, therefore, positive changes in soil moisture could be attributed to infiltration of rainfall through the surface. Depending on the nature of the surface, subsurface layers, level of traffic, etc., between 6 and 9% of rainfall was found to infiltrate through the road surfaces studied. The storm drainage generated by road runoff revealed a flow pattern similar to that of the receiving watercourse (River Thames) and increased with the increase of infiltration and soil water content below the road surface. The ratio of runoff to rainfall was 0Ð7, 0Ð9 and 0Ð5 for annual, winter (October-March) and summer (April-September) respectively. As the results of the infiltration indicated that 6 to 9% of annual rainfall infiltrates through the road surface, this means that evaporation represents, 21-24% of annual rainfall, with more evaporation taking place during summer than winter.

Spatial and temporal variability of rainfall and their effects on hydrological response in urban areas – a review

“…Ragab et al (2003) presented an experimental study of water fluxes in a residential area, in which they estimated infiltration and evaporation in urban areas, showing that the assumption that all rainfall becomes runoff is not correct and that it leads to an overestimation of runoff. Ramier et al (2011) studied the hydrological behaviour of urban streets over a 38-month period to estimate runoff losses and to better define rainfall runoff transformations.…”

“…The presence of leakage from drinking water and sewer networks can increase infiltration to groundwater and amount of contaminants that is spread from the sewer system into the soil (Salvadore et al, 2015). Although it is well known that not all rainfall turns into runoff (Boogaard et al, 2013;Lucke et al, 2014), it is common to consider the losses from impervious areas so small that they can be assumed negligible compared to the total runoff volume (Ragab et al, 2003;Ramier et al, 2011). Ragab et al (2003) tried to emphasize the importance of ac-counting for infiltration in the urban water balance, and found that infiltration through the road surface can constitute between 6 and 9 % of annual rainfall.…”

“…Although it is well known that not all rainfall turns into runoff (Boogaard et al, 2013;Lucke et al, 2014), it is common to consider the losses from impervious areas so small that they can be assumed negligible compared to the total runoff volume (Ragab et al, 2003;Ramier et al, 2011). Ragab et al (2003) tried to emphasize the importance of ac-counting for infiltration in the urban water balance, and found that infiltration through the road surface can constitute between 6 and 9 % of annual rainfall. Due to high spatial variability of infiltration, representative measurements are difficult to obtain and require a large amount of point-scale measurements (Boogaard et al, 2013;Lucke et al, 2014).…”

“…In their experimental study, Ragab et al (2003) showed that evaporation represents 21-24 % of annual rainfall, with more evaporation taking place during summer than winter. It is particularly important to have measurements with high resolution because a coarse spatial description can hide heterogeneous land covers and consequently, heterogeneous evaporation losses (Salvadore et al, 2015).…”

Water displacement by sewer infrastructure in the Grote Nete catchment, Belgium, and its hydrological regime effects

“…Imperviousness of urban areas is, however, very heterogeneous. Infiltration of impervious areas may not always be zero (Ragab et al, 2003). Impervious areas that are directly connected to the receiving river have a much larger effect on that receiving river (Boyd et al, 1994;Walsh et al, 2009).…”