Abstract
In Colombia, daily maximum multiannual series are one of the main inputs for design streamflow calculation, which requires performing a rainfall frequency analysis that involves several prior steps: (a) requesting the datasets, (b) waiting for the information, (c) reviewing the datasets received for missing or data different from the requested variable, and (d) requesting the information once again if it is not correct. To tackle these setbacks, 318 rain gauges located in the Colombian Caribbean region were used to first evaluate whether or not the Gumbel distribution was indeed the most suitable by performing frequency analyses using three different distributions (Gumbel, Generalized Extreme Value (GEV), and Log-Pearson 3 (LP3)); secondly, to generate daily maximum isohyetal maps for return periods of 2, 5, 10, 20, 25, 50, and 100 years; and, lastly, to evaluate which interpolation method (IDW, spline, and ordinary kriging) works best in areas with a varying density of data points. GEV was most suitable in 47.2% of the rain gauges, while Gumbel, in spite of being widely used in Colombia, was only suitable in 34.3% of the cases. Regarding the interpolation method, better isohyetals were obtained with the IDW method. In general, the areal maximum daily rainfall estimated showed good agreement when compared to the true values.
Highlights
Designing hydraulic structures for stormwater management encompasses several tasks, among which are: (a) watershed morphometric analysis, (b) estimation of the time of concentration,(c) calculation of the design rainfall via frequency analysis,(d) design flow computation, (e) sizing the hydraulic structure per se, and (f) hydraulic modeling to evaluate the structure’s hydraulic performance under various return periods
24h-max within regionalization ofof the maximum rainfall thatthat need to bemight further regionalization of the daily maximum rainfall trends within the departments that need to be further explored and analyzed, as it was observed that rainfall observations showed a noticeable increasing explored and analyzed, it was observed rainfall observations showed noticeable increasing or or decreasing trend lineasover time, whichthat may indicate (a) a change in thea rainfall pattern due to, decreasing trend line over time, whichand may (a) a change infrequency the rainfall patternisdue to,suitable among among others, anthropogenic factors (b)indicate that a non-stationary analysis more others, anthropogenic factors and (b) that a non-stationary frequency analysis is more suitable forand the for the rainfall data of those rain gauges at a local level [66,67]
Isohyetals by the Ordinary Kriging (OK) method (Figure 4c) evidenced: (a) the presence of small oval-shaped isohyetals with the same rainfall value of the larger oval they were within and (b) large areas between neighboring rain gauges with no isohyetals (“dead or no-variation zones”), which could affect the estimation of the areal precipitation for a given watershed
Summary
Designing hydraulic structures for stormwater management encompasses several tasks, among which are: (a) watershed morphometric analysis, (b) estimation of the time of concentration,(c) calculation of the design rainfall via frequency analysis (typically, under stationary conditions),(d) design flow computation, (e) sizing the hydraulic structure per se, and (f) hydraulic modeling to evaluate the structure’s hydraulic performance under various return periods. The design flow may be estimated via either a rainfall-runoff model or regression equations (in ungauged watersheds), or stationary frequency analysis of streamflow data, if available. The most common are: areas not covered due to either the absence of a rain gauge, or rain gauges no longer in service, or the rain gauges are mostly pluviometers (not pluviographs). The latter limits the ability to: (a) try to understand the real (measured) rainfall’s behavior during a day (its temporal distribution) and (b) derive, for instance, Intensity-Duration-Frequency (IDF) curves directly from registered time increments of daily rainfall (from pluviographs). Synthetic IDF curves are typically derived [1,2,3], which often need multiannual 24-h maximum rainfall (P24h-max ) as one of the main inputs to later estimate the rainfall (intensity) value associated with a selected return period: the design rainfall
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