Dear Mr. Achar,1. Methodology – The topographical sheets from survey of India were obtained to determine the drainage area from which rain water will reach into Jaisalmer city. The contours and natural drainage channels were marked on the topographical sheets. The catchment area has been calculated using ‘tracing graph paper’. The total drainage area was determined as 120 square km. The Jaisalmer city, existing drains and various proposed alignments of new drains were visited and discussions were held with the Collector Jaisalmer, officials of the Municipal Board, PWD (B&R), Railway department & BSF. The study also revealed that the Railway station & Jaisalmer-Jodhpur railway line are the lowest level portion in the city. Thus the natural drainage of the city is along the railway line. The rain water from all sides of city has a natural flow towards railway station. Thereafter I visited the natural drainage channel below the catchment area upto its outfall into a river. The survey of the proposed drains and natural drainage channel upto river was got done. Longitudinal sections and cross sections were prepared upto river. With the help of L-sections and X-sections, the design of drains and their cross drainage structures were designed. 2. Estimation of peak rainfall intensity by Statistical method The return period peak rainfall intensity and peak floods are estimated by statistical analysis, using available hydrological data at or around the site of the project./ structure. The statistical analysis is done to calculate peak rainfall intensities. Daily rainfall data of Jaisalmer city is available for the period year 1980 to 2007. Using this data, one day peak rainfall during a year has been identified. These peaks have been used for arriving at 1/2/5/10/25/50/100 year return period 24-hourly rainfall intensity by Gumbel Method, Least square method and Bell’s method. For one year return period only Bell’s formula is applicable. The Gumbel method is applicable for a storm having return period of 5 years or more. As per para 4.3 of IRC: SP: 50 – 1999, return period of one year has been adopted for estimation of run off from the catchment 3. Software used – Microsoft excel sheet was used for the calculations. No particular software was used. I understand, I have replied to your query. Do you have any other question? Regards Yogesh Agrawal

Published by

Dear Mr. Achar,

1. Methodology – The topographical sheets from survey of India were obtained to determine the drainage area from which rain water will reach into Jaisalmer city. The contours and natural drainage channels were marked on the topographical sheets. The catchment area has been calculated using ‘tracing graph paper’. The total drainage area was determined as 120 square km. The Jaisalmer city, existing drains and various proposed alignments of new drains were visited and discussions were held with the Collector Jaisalmer, officials of the Municipal Board, PWD (B&R), Railway department & BSF. The study also revealed that the Railway station & Jaisalmer-Jodhpur railway line are the lowest level portion in the city. Thus the natural drainage of the city is along the railway line. The rain water from all sides of city has a natural flow towards railway station. Thereafter I visited the natural drainage channel below the catchment area upto its outfall into a river. The survey of the proposed drains and natural drainage channel upto river was got done. Longitudinal sections and cross sections were prepared upto river. With the help of L-sections and X-sections, the design of drains and their cross drainage structures were designed.

2. Estimation of peak rainfall intensity by Statistical method

The return period peak rainfall intensity and peak floods are estimated by statistical analysis, using available hydrological data at or around the site of the project./ structure. The statistical analysis is done to calculate peak rainfall intensities. Daily rainfall data of Jaisalmer city is available for the period year 1980 to 2007. Using this data, one day peak rainfall during a year has been identified. These peaks have been used for arriving at 1/2/5/10/25/50/100 year return period 24-hourly rainfall intensity by Gumbel Method, Least square method and Bell’s method. For one year return period only Bell’s formula is applicable. The Gumbel method is applicable for a storm having return period of 5 years or more. As per para 4.3 of IRC: SP: 50 – 1999, return period of one year has been adopted for estimation of run off from the catchment

3. Software used – Microsoft excel sheet was used for the calculations. No particular software was used.

I understand, I have replied to your query. Do you have any other question?

Regards

Yogesh Agrawal