With the renewed emphasis on low-volume roads in South Africa, the use of low-level river crossings (LLRCs) will receive increased attention in the future. To evaluate LLRCs, it is necessary to know how often certain floods will occur and how long the structure can be expected to be submerged. From a functional design point of view, no guidelines exist on the size of openings required on an LLRC. The aim of the study is to quantify the extent of overtopping and provide a functional design method for the selection of LLRCs. The methodology is based on an analysis of historic river flow data obtained from the Department of Water Affairs of South Africa. Data were collected on several catchment areas with a variety of characteristics for a 20-year period. The 1-in-2-year flood was then determined for each catchment area. Considering various fractions of the 1-in-2-year flow, the number of times this flow was exceeded and the duration of excess flow were determined. This information was used as a basis for developing models to quantify the extent of overtopping. Based on these models, three levels of design were defined; namely, 0.25, 0.5, and 1.0 times the 1-in-2-year flood. It was accepted that, apart from passing under the structure, the design flood also may partially be accommodated over the structure. The acceptable flow depth for subcritical and supercritical flow during which a vehicle can pass over the structure was determined.


  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 112-117
  • Monograph Title: Modeling and model verification; testing pavement layers and materials; and low-cost drainage structures
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00715548
  • Record Type: Publication
  • ISBN: 0309061725
  • Files: TRIS, TRB
  • Created Date: Jan 2 1996 12:00AM