Properly designed and managed urban drainage systems with its interactions with other urban water systems are often lacking (Tucci, 2001). In cities of the developing countries urban development is dynamic and random. As cities develop, its impact on drainage include: increase in peak flows (up to 7 times) and in frequency owing to the higher runoff capacity through conduits and canals, and impermeabilization of surfaces increased sediment production from unprotected surfaces and production of solid waste (refuse) and deterioration in quality of surface and ground water owing to the transport of solid material and clandestine sewage and storm water connections (Tucci, 2001). Urbanization in developing countries is characterized by high population concentration in small areas, poor public transportation, inadequate basic infrastructure and social facilities, high level of pollution, and flooding (Ogbonna, 2014). This would require flow data at the point of entry to a storm sewer inlet, which is very difficult to obtain in practice. Note, we do not have supporting observational data at this scale to prove this assumption.
We felt it more rational to base our assessment of HRE setup options at the scale of an HRE, i.e., the area that drains to a storm sewer inlet, and judge the results in comparison to the most spatially explicit option. Conducting this as- sessment at the watershed scale would not only be tedious and time consuming to configure, but could be inappropri- ate because of potentially confounding effects introduced when the drainage network and groundwater algorithm are included in the simulation. The ar- rows represent flow routing directions. A rectangle without a dotted line means the subcatchment consists of a single (homoge- neous) subarea, either 100 % impervious or pervious. 5, each rectangle represents a subcatchment in SWMM, and the dotted line divides subar- eas within the subcatchment. Within this continuum, we chose to consider six plausible options for representing urban spatial constructs that are constrained by the SWMM subcatchment/subarea paradigm were examined (Fig. The opposite extreme would be a highly generalized subcatchment characterization where the entire area is modeled as one subcatchment with just two subareas, lumping all the spatial heterogeneity into a fictional space that has no basis in physical reality. This promises a decrease in model output uncertainty (Krebs et al., 2014 Sun et al., 2014), but requires specify- ing all the modeling parameters and unique flow directions among all subcatchments, results in longer computational times, and produces data management burdens that are typi- cally not practical. The most spatially refined approach to a SWMM setup (Option 1 in this study as presented below) would be to discretize every piece of im- pervious and pervious surface as an independent subcatch- ment. In the SWMM model setup just described we used a single sub- catchment setup that was based on the results of an anal- ysis done with the goal of determining which among a se- ries of plausible HRE configuration options strikes a balance among the degree of spatial and hydrologic aggregation, out- put uncertainty, and computational effort.
As mentioned earlier, an HRE can be modeled as a single subcatchment or multiple subcatchments in SWMM.
0 kommentar(er)
