Evaluation of Calculation Methods for Concentration and Peak Flow Times in Tropical Basins: Case of Rio Pacora, Panama
Distinguished Member, National Research System (SNI), Panama
Panama`s water resources greatly determine its economic activities1. Panama has an average annual precipitation and runoff of 3000 mm and 1764 mm respectively2, feeding 500 rivers and 52 basins3. If total precipitation is greater than the soil infiltration capacity, concentration and peak times (tp and tc) can be calculated. These values help to determine rainfall effects on cities/towns and economic activities. However, the equations widely used for the calculation of these parameters were obtained for areas with different characteristics than those existing in the tropics. This paper reviews the variability of results in these equations. As a case study, we use the Pacora River Basin, which is located between the coordinates 8 ° 00 `and 8 ° 20` N and 79 ° 15 `and 79 ° 30` W. It has a total area of 369 km2 divided in 6 sub-basins and 47 Km in its main stream. Its topography is varied, ranging from smooth slopes in the lower part (<8%) to steeper ones in the upper part (up to 75%)4 tp and tc were calculated by Kirpich`s methods5, "Curve Number "Of the SCS 6 and Johnston & Cross7.
Tc (hr) values of 6.6, 50.2 and 2.01 and tp (hr) of 4.6, 30 and 1.41 were obtained for Kirprich, SCS and Johnston & Cross respectively. In this sense, Kirprich and Johnston & Cross, may be the most appropriate for this basin. The SCS method even though considers topographical and land use aspects, fits better with basins under 800 Ha8. Total tp and tc values resulted from the summatory of tp and tc sub-basins values. This approach should give better total results since both Kirprich and specially the SCS method were developed for small basins.
From this work, we can conclude the necessity in tropical basins to have more monitoring and controlled experiments in order to validate existing methodologies.
1Espinosa et al.. (1997). Climate Research. Vol. 9.
2IHP. (2008). Balance Hídrico Superficial de Panamá: Período 1971-2002. PHI-VII/Documento Técnico No. 9.
3ANAM. 2011. II National Communication to the UNCCFC.
4Garcia and Valdés. (2009). Bachelor´s thesis, Universidad Tecnológica de Panamá.
5Kirpich, Z.P. (1940) Time of concentration of small agricultural watersheds. Civil Engineering, 10, 6.
6Soil Conservation Service. National Engineering Handbook, Section 4, Hydrology. Department of Agriculture, Washington. (1964 and 1972 editions)
7Johsntone and Cross. (1949) Elements of Applied Hydrology, Ronald Press, New York.
8Ven Te Chow, (1994). Hidrología para Ingenieros, McGraw Hill, Inc.
Powered by Eventact EMS