English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The objective of this paper is the generalization of IDF-formula for Litani River Basin-Lebanon following Bell (1969) & Chen (1969). Generalization is the use of a basic rainfall intensity at specific duration and frequency (i.e P1hr, T=10 years) to get the depth or Intensity of rainfall at different durations and return periods. This method is beneficial in developing countries where short duration rainfall data are not currently available. In this paper, a generalized IDF formula was developed based on a basic value of rainfall intensity as 100-year and 24 hours . Five available weather stations at Litani River Basin in Lebanon were used to gather different metrological conditions which may represent typical Mediterranean basin as well. In the first step of the research the SCS Type II distribution was used to derive short duration rainfall data from the available daily records. The derived data was used to get the Intensity-Duration Ratios & the Intensity Frequency ratios at each of the five stations upon which average ratios were obtained and optimized using least square method to get the “Chen” generalized formula parameters: = ( ) ( + ). The intensity values obtained by the generalized formula were validated by comparing to the original values which was obtained previously using frequency analysis. The results show a strong correlation with Average Mean Percentage Error “MAPE” of 4.38% at Tyre, 1.63% at Qaroun, 1.86% at Lebaa, 1.82% at Zahle and 3.98 % at Reyak station. The lack of adequate weather stations as well as sub-hourly and hourly rainfall data means that it is not possible to predict rainfall intensities over long return periods at several locations in Lebanon. In the second step of this paper, sub-hourly rainfall records, collected using four raingauages for a period of 3 years, were used to derive a generalized IDF formula based on (d=24hrs, T=2 years) rainfall intensity. Because the intensity-duration and the intensity-frequency ratios obtained from 3 years’ data are not fully representative for the ratios which Bell & Chen equations were built on (more than 20 years of historical records), the obtained generalized formula, which is based on only 3 years’ data, was considered to be correlated to the formula obtained in step 1 (based on 23 years daily records & SCS Type II distribution) by 3 function as follows: = F1 ∗ F2 ∗ ( ) F3 ∗ (μ + h). Where F1, F2 & F3 represent the correlation functions between & generalized IDF equations. ijas.ideasspread.org International Journal of Applied Science Vol. 4, No. 1; 2021 12 Published by IDEAS SPREAD • F1 = ∶ is the average ratio between the intensity I (T=100 Years, d=24 hours) and the measured raingauge intensity I (T=2 Years, d=24 hours) at each station. • F2 represent the relationship between the intensity-duration ratio obtained from 3 years’ gauge data and that obtained from 23 years recording data (using SCS Type II distribution). ( 23 ) = 2 ∗ (2 ) = 2 ∗ ( ) • F3 represent the relationship between intensity-frequency ratios obtained from 3 years’ gauge data and that obtained from 23 years recording data (using SCS Type II Distribution). (2 ) = 3 ∗ ( 23 ) = 3 ∗ (μ + h) The results show a strong correlation with Average Mean Percentage Error “MAPE” of 6.3% at Tyre, 3.67% at Qaroun, 4.12% at Lebaa, 4.21% at Zahle and 8.62 % at Reyak station. This method is beneficial in developing countries through which 3 years of available sub-hourly and hourly rainfall data could be used to develop IDF relationships.

Generalization of Intensity-Duration-Frequency Formula for Litani River Basin-Lebanon