Verification of the inlet capacities of modified stormwater kerb inlets and the development of new design curves

[摘要] ENGLISH ABSTRACT: Various aspects affecting the inlet capacities of modified stormwater kerb inlets wereinvestigated. Investigations centred on the influence of effective inlet length, ratios ofupstream transition section length to inlet section length and road crossfall. Thesuitability of existing design curves for use in the design of modified kerb inlets wasverified and new more user-friendly design curves were developed. Attempts weremade to develop a sound theoretical model to predict inlet capacities for stormwaterkerb inlets as the lack of such a model had previously been identified as a majorshortcoming in the design of stormwater kerb inlets.A detailed study of relevant literature and of various full scale model test resultsconfirmed the fact that the effective inlet length is the most important variableaffecting the inlet capacity at stormwater kerb inlets. Model studies on variouscombinations of transition section lengths and inlet section lengths have indicated thatin the case of supercritical flow the inlet capacity of stormwater kerb inlets is notsensitive to changes in the ratio between the inlet section length and the upstreamtransition section length. Furthermore no marked effect on the inlet capacity of amodified stormwater kerb inlet was detected when the road crossfall was increasedfrom 2% to 3%. The inlet capacities predicted by the existing design curves werefound to be consistent, although on the conservative side, when compared to the inletcapacities obtained from the full scale model tests. New design curves derived fromthe existing design curves were developed to provide a less cumbersome procedure inthe design of stormwater kerb inlets. The development of an improved comprehensivetheoretical model based on pure hydraulic principles was not possible due to theextremely complex nature of flow conditions at stormwater kerb inlets.The most important findings emanating from this research project are: - The confirmation of the effective inlet length concept, whereby a part of the expensive inlet section is replaced by an equivalent length of inexpensive transition section upstream of the kerb inlet. which does not affect the inlet capacity of the kerb inlet negatively and thereby results in a substantial savingin the cost of stormwater kerb inlets. - Model tests revealed that for supercritical flows the upstream transition sectioncan be made up to 6 times longer than the inlet section with a maximum lengthof 6m. without any negative effect on the inlet capacity of the kerb inlet.Similarly an analysis of previous research results has indicated that even incases of subcritical flow the upstream transition section can be made twice thelength of the inlet section. - The full scale model tests also indicated that an upward adjustment of 30% inthe inlet capacities as predicted by the existing design curves was justified. Themodified design curves proved to be suitable for the design of conventionalstormwater kerb inlets as well as for modified stormwater kerb inlets wherepart of the inlet section is replaced by a transition section. A new set of easyto use design curves was developed specifically for urban applications. - Guidelines for determining upstream transition section lengths were drawn upfor use in conjunction with the existing and new design curves for the designof stormwater kerb inlets.

[发布机构] Stellenbosch University