Effect of the Non-Stationarity of Rainfall Events on the Design of Hydraulic Structures for Runoff Management and Its Applications to a Case Study at Gordo Creek Watershed in Cartagena de Indias, Colombia

Abstract

Abstract:The 24-h maximum rainfall (P 24h-max ) observations recorded at the synoptic weather station of Rafael Núñez airport (Cartagena de Indias, Colombia) were analyzed, and a linear increasing trend over time was identified. It was also noticed that the occurrence of the rainfall value (over the years of record) for a return period of 10 years under stationary conditions (148.1 mm) increased, which evidences a change in rainfall patterns. In these cases, the typical stationary frequency analysis is unable to capture such a change. So, in order to further evaluate rainfall observations, frequency analyses of P 24h-max for stationary and non-stationary conditions were carried out (by using the generalized extreme value distribution). The goodness-of-fit test of Akaike Information Criterion (AIC), with values of 753.3721 and 747.5103 for stationary and non-stationary conditions respectively, showed that the latter best depicts the increasing rainfall pattern. Values of rainfall were later estimated for different return periods (2,5,10,25, 50, and 100 years) to quantify the increase (non-stationary versus stationary condition), which ranged 6% to 12% for return periods from 5 years to 100 years, and 44% for a 2-year return period. The effect of these findings were tested in the Gordo creek watershed by first calculating the resulting direct surface runoff (DSR) for various return periods, and then modeling the hydraulic behavior of the downstream area (composed of a 178.5-m creek's reach and an existing box-culvert located at the watershed outlet) that undergoes flooding events every year. The resulting DSR increase oscillated between 8% and 19% for return periods from 5 to 100 years, and 77% for a 2-year return period when the non-stationary and stationary scenarios were compared. The results of this study shed light upon to the precautions that designers should take when selecting a design, based upon rainfall observed, as it may result in an underestimation of both the direct surface runoff and the size of the hydraulic structures for runoff and flood management throughout the city.

Analysis of the Behavior of Daily Maximum Rainfall within the Department of Atlántico, Colombia

“…Overall, the Gumbel distribution was the best fit in 63.2% of the 19 rain gauges analyzed, while GEV was the best fit in only 36.8%. These results represent a shift from the findings by González-Álvarez et al [45], where GEV was best in 53.8% of the 13 rain gauges assessed. This is due to the fact that the Gumbel distribution was the best CDF among the new additional six rain gauges analyzed in this study.…”

“…The non-stationary frequency analysis was performed according to the methodology proposed by Obeysekera and Salas [1,43,44], which uses (a) the GEV function by varying the location parameter over time and maintaining the constant parameters of scale and shape (called GEVmu), and (b) a definition of the return period (Tr) according to the geometric distribution given by Equation (20), where Pj is the is the time-varying exceedance probability, and j represents the year to be projected [1,45]. The GEVmu function was already tested by Gonzalez-Alvarez et al [45] in the Colombian Caribbean region, where a sensitivity analysis showed that varying the shape and/or scale parameters did not bring any improvement in the performance of either GEV or Gumbel distributions.…”

Isohyetal Maps of Daily Maximum Rainfall for Different Return Periods for the Colombian Caribbean Region

“…Scatter plots of the multiannual series of P 24h-max of each rain gauge revealed that there might be 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 or decreasing trend line over time, which may indicate (a) a change in the rainfall pattern due to, among others, anthropogenic factors and (b) that a non-stationary frequency analysis is more suitable for the rainfall data of those rain gauges at a local level [66,67]. Figure 3 shows the scatter plot and the trend lines of the rain gauges Puerto Giraldo and Los Campanos located in the department of Atlántico.…”

Selection of Hydrological Probability Distributions for Extreme Rainfall Events in the Regions of Colombia

“…In recent years, due to the influence of global warming as well as changes in the magnitude and patterns of extreme precipitation events, it is necessary to periodically update the magnitudes of the maximum rainfall that are used to design hydraulic works [7]. In particular, extreme weather events such as floods, droughts and storms can increase in frequency over time [8][9][10]; thus, it is necessary to determine probability functions that best represent current trends in the data.…”