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

Grobler, Pieter (Stellenbosch : Stellenbosch University, 1994-03)

Thesis (MEng)--Stellenbosch University, 1994.

Thesis

ENGLISH ABSTRACT: Various aspects affecting the inlet capacities of modified stormwater kerb inlets were investigated. Investigations centred on the influence of effective inlet length, ratios of upstream transition section length to inlet section length and road crossfall. The suitability of existing design curves for use in the design of modified kerb inlets was verified and new more "user-friendly" design curves were developed. Attempts were made to develop a sound theoretical model to predict inlet capacities for stormwater kerb inlets as the lack of such a model had previously been identified as a major shortcoming in the design of stormwater kerb inlets. A detailed study of relevant literature and of various full scale model test results confirmed the fact that the effective inlet length is the most important variable affecting the inlet capacity at stormwater kerb inlets. Model studies on various combinations of transition section lengths and inlet section lengths have indicated that in the case of supercritical flow the inlet capacity of stormwater kerb inlets is not sensitive to changes in the ratio between the inlet section length and the upstream transition section length. Furthermore no marked effect on the inlet capacity of a modified stormwater kerb inlet was detected when the road crossfall was increased from 2% to 3%. The inlet capacities predicted by the existing design curves were found to be consistent, although on the conservative side, when compared to the inlet capacities obtained from the full scale model tests. New design curves derived from the existing design curves were developed to provide a less cumbersome procedure in the design of stormwater kerb inlets. The development of an improved comprehensive theoretical model based on pure hydraulic principles was not possible due to the extremely 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 saving in the cost of stormwater kerb inlets. - Model tests revealed that for supercritical flows the upstream transition section can be made up to 6 times longer than the inlet section with a maximum length of 6m. without any negative effect on the inlet capacity of the kerb inlet. Similarly an analysis of previous research results has indicated that even in cases of subcritical flow the upstream transition section can be made twice the length of the inlet section. - The full scale model tests also indicated that an upward adjustment of 30% in the inlet capacities as predicted by the existing design curves was justified. The modified design curves proved to be suitable for the design of conventional stormwater kerb inlets as well as for modified stormwater kerb inlets where part of the inlet section is replaced by a transition section. A new set of "easy to use" design curves was developed specifically for urban applications. - Guidelines for determining upstream transition section lengths were drawn up for use in conjunction with the existing and new design curves for the design of stormwater kerb inlets.

AFRIKAANSE OPSOMMING: Verskeie aspekte wat die inlaatkapasiteit van verbeterde randsteeninlate belnvloed is ondersook. Die belangrikste aspekte wat ondersoek is, was die invlood van effektiewe inlaatlengte en die moontlike verhouding van die stroomop oorgangslengte tot die werklike inlaatlengte sowel as dwarshelling. Die ontwerpgrafieke wat tans gebruik word om randsteeninlaatlengtes te bepaal is ook ondersoek aan die hand van modeltoetse op volskaalse modelle om die grafieke se akkuraatheid te toots. Meer gebruikersvriendelike ontwerpgrafieke is ook ontwikkel. 'n Belangrike tekortkoming tot op datum, naamlik 'n geskikte teoretiese model om die inlaatkapasiteit van randsteeninlate te beskryf, is aangespreek. 'n Voorvereiste vir so 'n model was dat die model gebaseer moes word op suiwer hidrouliese beginsels. Die bestudering van vorige navorsing asook die uitvoering van verskeie modelstudies op volskaalse randsteeninlate het die effektiewe inlaatlengte as die belangrikste veranderlike wat die inlaatkapasiteit van randsteeninlate bepaal geYdentifiseer. Tydens tootse uitgevoer op volskaalse modelle onder superkritiese vlooitoostande met verskillende kombinasies van oorgangslengtes en inlaatlengtes, vir die dieselfde totale lengte het dit geblyk dat die inlaatkapasiteit grootliks onatbanklik is van die verhouding van die oorgangslengte tot die inlaatlengte. Vit die modeltootse het dit oak geblyk dat paddwarsval 'n baie beperkte invlood op die inlaatkapasiteit van ransteeninlate gehad het toe die paddwarsval verander is van 2%na 3%. Die resultate wat verkry is uit die modeltoetse het ook aangetoon dat die bestaande ontwerpgrafieke konserwatief is in hul voorspelling van inlaatkapasieit van randsteeninlate. Die bestaande ontwerpgrafieke is voorts gebruik om nuwe meer gebruikersvriendelike ontwerpgrafieke te ontwikkel. Die ontwikkeling van 'n teoretiese model am inlaatkapasiteite volledig te voorspel was egter nie moontlik nie vanwee die uiters komplekse aard van die vloei by randsteeninlate. Die belangrikste bevindinge van hierdie studie kan soos volg opgesom word: - Afdoende bewyse is gevind dat die "effektiewe inlaatlengte" konsep, waarvolgens 'n gedeelte van die duur inlaatgedeelte met 'n goedkoper oorgangsstuk van dieselfde Iengte vervang kan word sonder om inlaatkapasiteit in te boet, weI suksesvol aangewend kan word om kostes in die ontwerp van stOlIDwater randsteeninlate te bespaar. - Afdoende bewyse is gevind dat die "effektiewe inlaatlengte" konsep, waarvolgens 'n gedeelte van die duur inlaatgedeelte met 'n goedkoper oorgangsstuk van dieselfde Iengte vervang kan word sonder om inlaatkapasiteit in te boet, weI suksesvol aangewend kan word om kostes in die ontwerp van stOlIDwater randsteeninlate te bespaar. - Afdoende bewyse is gevind dat die "effektiewe inlaatlengte" konsep, waarvolgens 'n gedeelte van die duur inlaatgedeelte met 'n goedkoper oorgangsstuk van dieselfde Iengte vervang kan word sonder om inlaatkapasiteit in te boet, weI suksesvol aangewend kan word om kostes in die ontwerp van stOlIDwater randsteeninlate te bespaar. - Riglyne is ook ontwikkel vir die bepaling van stroomop oorgangslengtes. Die riglyne kan saam met die bestaande en die nuwe ontwerpgrafieke gebruik word by die ontwerp van stormwater nmdsteeninlate.

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