Green roofs play a significant role in sustainable drainage systems. They form absorbent surfaces for rainwater, which they retain with the aid of profile and plants. Such roofs therefore take an active part in improving the climatic conditions of a city and, more broadly, the water balance of urbanized areas. One of the factors influencing the hydrological efficiency of green roofs is the drainage layer. In the article, column studies were carried out under field conditions involving the comparison of the retention abilities of two aggregates serving as the drainage layer of green roofs, i.e. Leca® and quartzite grit. The average retention of the substrate was 48%; for a 5 cm drainage layer of Leca® retention was 57%, for a 10 cm layer of Leca average retention was 61%. For a 5 cm layer of quartzite grit average retention was 50%, for 10 cm layer of quartzite grit 53%. The highest retention was obtained for the column with the substrate and 10-centimeter layer of Leca®. At the same time, it was shown that Leca® is a better retention material than quartzite grit. The initial state of substrate moisture content from a green roof appears to be a significant factor in reducing rainfall runoff from a green roof; the ob-tained values of initial moisture content made for a higher correlation than the antecedent dry weather period.
Runoff estimation is a key component in various hydrological considerations. Estimation of storm runoff is especially important for the effective design of hydraulic and road structures, for the flood flow management, as well as for the analysis of land use changes, i.e. urbanization or low impact development of urban areas. The curve number (CN) method, developed by Soil Conservation Service (SCS) of the U.S. Department of Agriculture for predicting the flood runoff depth from ungauged catchments, has been in continuous use for ca. 60 years. This method has not been extensively tested in Poland, especially in small urban catchments, because of lack of data. In this study, 39 rainfall-runoff events, collected during four years (2009–2012) in a small (A=28.7 km2), urban catchment of Służew Creek in southwest part of Warsaw were used, with the aim of determining the CNs and to check its applicability to ungauged urban areas. The parameters CN, estimated empirically, vary from 65.1 to 95.0, decreasing with rainfall size and, when sorted rainfall and runoff separately, reaching the value from 67 to 74 for large rainfall events.
This study presents the results of tests conducted in 2009 and 2010 on experimental sites installed on the roof of the Science and Education Building of the Wroclaw University of Environmental and Life Sciences. The aim of the analysis was to determine the retention capacity of green roofs and the runoff delays and peak runoff reduction during rainfall recorded in Wroclaw conditions.
The research shows that green roofs allow to reduce the volume of runoff stormwater in comparison to conventional roofs, that they delay the runoff in time and influence the reduction of the maximum runoff intensity, and thus may limit the impact of stormwater on the stormwater drainage and combined sewage systems.
Time of concentration, Tc, is defined as time elapsed from the beginning of rainfall infiltrated into soil layer until it reaches a constant infiltration rate (fc) which is indicated an equilibrium subsurface flow rate. In hydrological view, time of concentration plays a significant role in elaboration of transformation of rainfall into runoff in a watershed. The aims of this research are to define influence of soil density and soil water content in determining time of concentration using infiltration concept based on water balance theory, and to find out the effect of land slope this time. Watershed laboratory experiment using rainfall simulator was employed to examine time of concentration associated with infiltration process under different slope, soil density and soil water content based on water balance concept. The steady rainfall intensity was simulated using sprinklers which produced 2 dm3∙min–1. Rainfall, runoff and infiltration analysis were carried out at laboratory experiment on soil media with varied of soil density (d) and soil water content (w), where variation of land slopes (s) were designed in three land slopes 2, 3 and 4%. The results show that relationship between soil density and land slope to time of concentra-tion showed a quadratic positive relationship where the higher the soil density address to the longer time of concentration. Moreover, time of concentration had an inverse relationship with soil water content and land slope that means time of con-centration decreased when the soil water content increased.
Flood inundation processes in urban areas are primarily affected by artificial factors such as drainage facilities, local al-terations of topography and land uses. The objective of this study is to examine the capability of hydrological model SI-MODAS to estimate runoff and investigating the utilization of storage well in controlling runoff in a residential area. The result of the estimated runoff from the hydrological model was compared with the existing capacity of the drainage channel to identify which channel experienced the problem of inundation. The location of inundation was used to determine the location and number of storage well. The results showed that SIMODAS model could be applied in runoff analyses with 8.09% of relative error compared with runoff depth from field measurement. The existing capacity of the channel could not accommodate runoff Q10yr where the inundation discharge was approximately 0.24 m3·s–1 (at outlet point 1) and 0.12 m3·s–1 (at outlet point 2). The inundation problem was overcome by using a combination system between channel normalization (reduce 35% of total inundation discharge) and storage well system (reduce 65% of total inundation discharge). The storage well was designed at 20 locations (at outlet point 1) and 16 locations (at outlet point 2) which each well had a discharge of 0.0058 m3·s–1. The storage well combined with channel normalization could be used as an alternative way to solve inunda-tion problems in a residential area considering the constraint of land space limitation in the urban area.
The runoff coefficient is one of the fundamental hydrological characteristics of a catchment. It indicates a share of the precipitation water that runs off from the catchment.
The results of the runoff coefficient calculation based on measurements carried out continuously in the Cerhovický Stream catchment over a considerable period of time, i.e. from 1988 up to 2006 are presented. The precipitation and runoff data in the catchment were used. Mean value of the runoff coefficient and the runoff coefficients for the agricultural and forest parts of the catchment are presented. The total mean runoff coefficient for the Cerhovický Stream is 0.19 with the standard deviation of 0.06. Mean runoff coefficient for the forest part is 0.13 and for the agricultural part – 0.24.
Differences between the years with a higher and a lower precipitation were followed as well. We also statistically evaluated possible hydrological changes caused by the construction of the highway and the market centre. For another possible explanation of quite high standard deviation of the mean annual runoff coefficient we followed the monthly runoff coefficient dependence on water temperature and of ground water table depth.