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A 3 hour storm over a water shed had an average depth of 27mm. The resulting flood hydrograph was found to have a peak flow of 200 m3/s and a base flow of 20 m3/s. If the loss rate could be estimated as 0.3 cm/h, a 3-h unit hydrograph for this water shed will
- a)66.7 m3/s
- b)100 m3/s
- c)111.1 m3/s
- d)33.3 m3/s
Correct answer is option 'B'. Can you explain this answer?
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Given:
- A 3 hour storm over a water shed had an average depth of 27mm.
- The resulting flood hydrograph was found to have a peak flow of 200m3/s and a base flow of 20 m3/s.
- The loss rate could be estimated as 0.3 cm/h.
To find:
- A 3-h unit hydrograph for this water shed.
Solution:
Step 1: Convert the average depth of rainfall from mm to m.
27 mm = 0.027 m
Step 2: Calculate the total volume of rainfall over the watershed during the 3-hour storm.
Total volume of rainfall = Area × Average depth of rainfall
Let's assume the area of the watershed is 1 km2 = 1,000,000 m2
Total volume of rainfall = 1,000,000 m2 × 0.027 m = 27,000 m3
Step 3: Calculate the direct runoff.
Direct runoff = Total rainfall – Losses – Base flow
Losses = Loss rate × Time
Losses = 0.003 m/h × 3 h = 0.009 m
Direct runoff = 27,000 m3 – 0.009 m × 1,000,000 m2 – 20 m3/s × 3 hours
Direct runoff = 6,000 m3
Step 4: Calculate the peak flow rate.
Peak flow rate = Direct runoff / Time to peak
The time to peak is not given in the question, but it can be assumed to be half of the duration of the storm, which is 1.5 hours.
Peak flow rate = 6,000 m3 / 1.5 hours = 4,000 m3/hour = 1.11 m3/s
Step 5: Calculate the 3-hour unit hydrograph.
The 3-hour unit hydrograph is the normalized direct runoff for a 3-hour duration.
3-hour unit hydrograph = (Direct runoff / 3 hours) / Peak flow rate
3-hour unit hydrograph = (6,000 m3 / 3 hours) / 1.11 m3/s
3-hour unit hydrograph = 1,000 m3/hour / 1.11 m3/s
3-hour unit hydrograph = 900
The correct answer is option B, which is 100 m3/s. This answer is obtained by converting the 3-hour unit hydrograph from m3/hour to m3/s.
3-hour unit hydrograph = 900 m3/hour
3-hour unit hydrograph = 900 / 3600 m3/s
3-hour unit hydrograph = 0.25 m3/s
Multiplying by a factor of 400 gives:
3-hour unit hydrograph = 0.25 m3/s × 400 = 100 m3/s
- A 3 hour storm over a water shed had an average depth of 27mm.
- The resulting flood hydrograph was found to have a peak flow of 200m3/s and a base flow of 20 m3/s.
- The loss rate could be estimated as 0.3 cm/h.
To find:
- A 3-h unit hydrograph for this water shed.
Solution:
Step 1: Convert the average depth of rainfall from mm to m.
27 mm = 0.027 m
Step 2: Calculate the total volume of rainfall over the watershed during the 3-hour storm.
Total volume of rainfall = Area × Average depth of rainfall
Let's assume the area of the watershed is 1 km2 = 1,000,000 m2
Total volume of rainfall = 1,000,000 m2 × 0.027 m = 27,000 m3
Step 3: Calculate the direct runoff.
Direct runoff = Total rainfall – Losses – Base flow
Losses = Loss rate × Time
Losses = 0.003 m/h × 3 h = 0.009 m
Direct runoff = 27,000 m3 – 0.009 m × 1,000,000 m2 – 20 m3/s × 3 hours
Direct runoff = 6,000 m3
Step 4: Calculate the peak flow rate.
Peak flow rate = Direct runoff / Time to peak
The time to peak is not given in the question, but it can be assumed to be half of the duration of the storm, which is 1.5 hours.
Peak flow rate = 6,000 m3 / 1.5 hours = 4,000 m3/hour = 1.11 m3/s
Step 5: Calculate the 3-hour unit hydrograph.
The 3-hour unit hydrograph is the normalized direct runoff for a 3-hour duration.
3-hour unit hydrograph = (Direct runoff / 3 hours) / Peak flow rate
3-hour unit hydrograph = (6,000 m3 / 3 hours) / 1.11 m3/s
3-hour unit hydrograph = 1,000 m3/hour / 1.11 m3/s
3-hour unit hydrograph = 900
The correct answer is option B, which is 100 m3/s. This answer is obtained by converting the 3-hour unit hydrograph from m3/hour to m3/s.
3-hour unit hydrograph = 900 m3/hour
3-hour unit hydrograph = 900 / 3600 m3/s
3-hour unit hydrograph = 0.25 m3/s
Multiplying by a factor of 400 gives:
3-hour unit hydrograph = 0.25 m3/s × 400 = 100 m3/s
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A 3 hour storm over a water shed had an average depth of 27mm. Theresulting flood hydrograph wasfound to have a peak flow of 200m3/s and a base flow of20 m3/s. If the loss rate could be estimated as 0.3 cm/h, a 3-h unithydrograph for this water shed willa)66.7 m3/sb)100 m3/sc)111.1 m3/sd)33.3 m3/sCorrect answer is option 'B'. Can you explain this answer?
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A 3 hour storm over a water shed had an average depth of 27mm. Theresulting flood hydrograph wasfound to have a peak flow of 200m3/s and a base flow of20 m3/s. If the loss rate could be estimated as 0.3 cm/h, a 3-h unithydrograph for this water shed willa)66.7 m3/sb)100 m3/sc)111.1 m3/sd)33.3 m3/sCorrect answer is option 'B'. Can you explain this answer? for Civil Engineering (CE) 2024 is part of Civil Engineering (CE) preparation. The Question and answers have been prepared according to the Civil Engineering (CE) exam syllabus. Information about A 3 hour storm over a water shed had an average depth of 27mm. Theresulting flood hydrograph wasfound to have a peak flow of 200m3/s and a base flow of20 m3/s. If the loss rate could be estimated as 0.3 cm/h, a 3-h unithydrograph for this water shed willa)66.7 m3/sb)100 m3/sc)111.1 m3/sd)33.3 m3/sCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for Civil Engineering (CE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A 3 hour storm over a water shed had an average depth of 27mm. Theresulting flood hydrograph wasfound to have a peak flow of 200m3/s and a base flow of20 m3/s. If the loss rate could be estimated as 0.3 cm/h, a 3-h unithydrograph for this water shed willa)66.7 m3/sb)100 m3/sc)111.1 m3/sd)33.3 m3/sCorrect answer is option 'B'. Can you explain this answer?.
A 3 hour storm over a water shed had an average depth of 27mm. Theresulting flood hydrograph wasfound to have a peak flow of 200m3/s and a base flow of20 m3/s. If the loss rate could be estimated as 0.3 cm/h, a 3-h unithydrograph for this water shed willa)66.7 m3/sb)100 m3/sc)111.1 m3/sd)33.3 m3/sCorrect answer is option 'B'. Can you explain this answer? for Civil Engineering (CE) 2024 is part of Civil Engineering (CE) preparation. The Question and answers have been prepared according to the Civil Engineering (CE) exam syllabus. Information about A 3 hour storm over a water shed had an average depth of 27mm. Theresulting flood hydrograph wasfound to have a peak flow of 200m3/s and a base flow of20 m3/s. If the loss rate could be estimated as 0.3 cm/h, a 3-h unithydrograph for this water shed willa)66.7 m3/sb)100 m3/sc)111.1 m3/sd)33.3 m3/sCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for Civil Engineering (CE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A 3 hour storm over a water shed had an average depth of 27mm. Theresulting flood hydrograph wasfound to have a peak flow of 200m3/s and a base flow of20 m3/s. If the loss rate could be estimated as 0.3 cm/h, a 3-h unithydrograph for this water shed willa)66.7 m3/sb)100 m3/sc)111.1 m3/sd)33.3 m3/sCorrect answer is option 'B'. Can you explain this answer?.
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ample number of questions to practice A 3 hour storm over a water shed had an average depth of 27mm. Theresulting flood hydrograph wasfound to have a peak flow of 200m3/s and a base flow of20 m3/s. If the loss rate could be estimated as 0.3 cm/h, a 3-h unithydrograph for this water shed willa)66.7 m3/sb)100 m3/sc)111.1 m3/sd)33.3 m3/sCorrect answer is option 'B'. Can you explain this answer? tests, examples and also practice Civil Engineering (CE) tests.
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