On-line version ISSN 1816-7950
Print version ISSN 0378-4738
Water SA vol.34 n.3 Pretoria Mar. 2008
DM Knoesen; JC Smithers
School of Bioresources Engineering and Environmental Hydrology, University of KwaZulu-Natal, P/Bag X01, Scottsville, South Africa
The temporal distribution of rainfall, viz. the distribution of rainfall intensity during a storm, is an important factor affecting the timing and magnitude of peak flow from a catchment and hence the flood-generating potential of rainfall events. Rainfall intensity is also one of the primary inputs into hydrological models used for the design of hydraulic structures. In the absence of continuously recorded rainfall data, one method of estimating the temporal distribution of rainfall is to disaggregate coarser-scale data into a finer resolution, e.g. from daily data into hourly rainfall information. In this study, a daily to hourly disaggregation model developed in Australia, and modified for application in South Africa, is used. However, this model requires input obtained from short-duration data at the desired location. Owing to the paucity of short-duration data in South Africa, the methodology is regionalised to enable the application of the model at a national scale, particularly at locations where only daily data are available. The regionalised model was independently tested at 15 locations in differing climatic regions in South Africa. At each location, observed hourly data were aggregated to yield daily values and were then disaggregated using the methodology. Results show that the regionalised model is capable of replicating the results obtained when 'at-site' short duration rainfall data are used as input to the disaggregation model, and is able to retain the daily totals and the statistical characteristics of the hourly rainfall.
Keywords: temporal rainfall disaggregation, regionalisation, South Africa
"Full text available in PDF"
BOUGHTON W (2000) A Model for Disaggregating Daily to Hourly Rainfalls for Design Flood Estimation. Cooperative Research Centre for Catchment Hydrology. Report No 00/15. Monash University, Clayton, Victoria, Australia. 36 pp. [ Links ]
GYASI-AGYEI Y (1999) Identification of regional parameters of a stochastic model for rainfall disaggregation. J. Hydrol. 223 148-163. [ Links ]
KNOESEN DM (2005) The Development and Assessment of Techniques for Daily Rainfall Disaggregation in South Africa. Unpublished M.Sc. Thesis, University of KwaZulu-Natal, Pietermaritzburg, RSA. 88 pp. [ Links ]
KOUTSOYIANNIS D and ONOF C (2001) Rainfall disaggregation using adjusting procedures on a Poisson cluster model. J. Hydrol. 246 109-122. [ Links ]
MIKKELSEN PS, MADSEN H, ARNBJERG NIELSEN K, JORGENSEN HK, ROSBJERG D and HARREMOES P (1998) A rationale for using local and regional point rainfall data for design and analysis of urban storm drainage systems. Water Sci. Technol. 37 (11) 7-14. [ Links ]
SMITHERS JC and SCHULZE RE (2000a) Development and Evaluation of Techniques for Estimating Short Duration Design Rainfall in South Africa. WRC Report No. 681/1/00. Water Research Commission, Pretoria, RSA. 356 pp. [ Links ]
SMITHERS JC and SCHULZE RE (2000b) Long Duration Design Rainfall Estimates for South Africa. WRC Report No. 811/1/00. Water Research Commission, Pretoria, RSA. 69 pp. [ Links ]
Received 16 October 2007;
Accepted in revised form 28 May 2008.