Influence and modelling of urban runoff on the peak flows in rivers.
Surface waters and urban drainage systems are usually studied separately. However there are important interactions between both systems. Urban drainage systems can have an important impact on the surface waters, mainly at combined sewer overflows. On the other hand during periods of high water levels in a river, the runoff from the urban drainage system can be significantly influenced by backwater, which increases the probability of flooding in is not obvious, because the modelling tools for both systems are often hard to combine properly. To properly assess the probability of flooding for this kind of integrated water systems, different submodels are needed for both subsystems. In practice often one single model is used to describe the runoff to rivers despite the presence of urban catchments. The main objective of this study is to show the limits of this simplified approach. Furthermore, it is necessary to use continuous long term simulations, because of the differences in runoff behaviour. Detailed hydrodynamic models do not really fit for this purpose because of long simulation times and high demands in memory and disk space. Therefore simplified conceptual models are more useful.
Impact of the two-directional interaction of sewer and river systems on the flood risk
Sewer networks and river systems are often studied in a separate way. They may, however, interact in two directions. The first direction is straightforwa rd: sewer effluent and overflow discharges increase the flow and the water levels in the receiving river. In the opposite direction, during storm conditions, high river levels may obstruct urban storm drainage into the river, and consequently the flood risk along the sewer system may increase. This influence was studied for the Erpe-Mere Municipality combined sewer system in Belgium. Firstly, composite and short duration storm simulati ons were performed using detailed hydrodynamic SOBEK models. The results of these simulations were used to calibrate simplified conceptual models, which enabled simulation of long historical time series and statistical analysis of simulation results. The study validated the presumption that the sewer-river two-directional interaction enhances both sewer and river flood risks and therefore recommended this effect be taken into consideration during sewer and river infrastructures design. The study recommended and demonstrated the use of simplified models, which after calibration to the full hydrodynamic models using synthetic storms for a ra nge of low to high return periods, reached nearly the same accuracy as the corresponding detailed models but advantageously with shorter computational time.
Archaeology and mud wall decay in a West African village
Abstract A detailed study of the processes of deterioration of mud walls and of the physical evolution and devolution of a contemporary West African village is seen to facilitate the location of decayed mud structures at a nearby archaeological site. Various climatic and pedological conditions at the site make it unlikely that such walls will be discerned. The archaeologist wishing to obtain the fullest and least biased picture of the settlement configuration of the ancient community should therefore heed all the inferential lessons to be had from a focused ethnographic investigation. Given similar climatic situations and practices of house construction, taphonomy and ethnographic analogies may both be necessary for a valid reconstruction of an archaeological settlement.