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In the study area, the rainfall analysis shows that local distribution, short durations, and high intensities are the most distinctive features of these rainfall events (Figure 5). The annual average rainfall in the Abu Arish area does not exceed 211 mm (Tables 2 and 3). Temporally, most rainfall events occur in April and between July and October. Spatially, the eastern mountainous area has more rainfall than the western plain area, and the sloping land of the eastern area causes a sharp drop in the watershed's ability to conserve water, especially in the eastern part as ground slopes vary between 52 and 82° (Figure 4(b)). Statistical frequency analyses of 46 years’ (1963–2009) available data show a highly erratic trend in rainfall patterns, with both positive and negative deviations from the mean value (Tables 2 and 3, and Figures 5 and 6). From these analyses, projections were made for annual 1 day maximum rainfall, and 2–5 day consecutive maximum rainfall, corresponding to return periods. The area has a recorded maximum rainfall of 126 mm (Tables 2 and 3, and Figures 6 and 7). IDF curves were developed using Gumbel frequency analysis techniques, where c, m, and e parameters are 411.10, 81.0, and 0.76, respectively (Figure 7). The 10 minute rainfall intensity varies between 80 and 160 mm/hr for 2 and 100 year return periods. IDF curves like these are a useful aid when designing drainage works for any project and facilitate the design of safe and economical flood control measures.
Table 2

Statistics of the 24 hr rainfall depths (mm) at Abu Arish metrological station

Number of observations46  
Minimum (Max6.90 Median  38.5 
Maximum (Min126.00 Coefficient of variation (Cv0.54 
Mean  41.10 Skewness coefficient (Cs1.42 
Standard deviation (σ) 22.30 Kurtosis coefficient (Ck5.82 
Number of observations46  
Minimum (Max6.90 Median  38.5 
Maximum (Min126.00 Coefficient of variation (Cv0.54 
Mean  41.10 Skewness coefficient (Cs1.42 
Standard deviation (σ) 22.30 Kurtosis coefficient (Ck5.82 
Table 3

Twenty-four hour rainfall depths estimated for different return periods at Abu Arish metrological station

Return period (years)5102550100
24 hr rainfall height (mm) 57.18 70.23 86.76 98.95 111.13 
Return period (years)5102550100
24 hr rainfall height (mm) 57.18 70.23 86.76 98.95 111.13 
Figure 5

Annual rainfall of Saudi Arabia (National Center for Atmospheric Research 2008).

Figure 5

Annual rainfall of Saudi Arabia (National Center for Atmospheric Research 2008).

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Figure 6

Twenty-four hour rainfall depths and cumulative probability (Gumbel) at Abu Arish.

Figure 6

Twenty-four hour rainfall depths and cumulative probability (Gumbel) at Abu Arish.

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Figure 7

IDF curves computed by Gumbel method at Abu Arish area (2–100 years).

Figure 7

IDF curves computed by Gumbel method at Abu Arish area (2–100 years).

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