GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER-VII (NEW) EXAMINATION - WINTER 2018
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Subject Code: 2174001
Subject Name: Irrigation and Water Resources Engineering
Date: 15/11/2018
Time: 10:30 AM TO 01:00 PM
Total Marks: 70
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Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
Q.1
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(a) A river reach has a flood wave passing through it. At a given instant the storage of water in the reach was estimated as 15.5 ha.m. What would be the storage in the reach after an interval of 3 hours if the average inflow and outflow during the time period are 14.2 m3/s and 10.6 m3/s respectively ? [03]
(b) Prepare the flowchart for the steps followed in determining areal mean rainfall for a particular catchment using a GIS tool (QGIS), correlate with the term project carried out and present the flowchart accordingly? [07]
(c) The average monthly streamflow values in a river are 150, 200, 420, 400, 350, 290, 320, 230, 250, 210, 180 and 100 (m3/s). Prepare a flow duration curve for this river using this data and answer the following. [04]
- What is the value of firm power corresponding to 90% dependable flow?
- What is the value of 75% dependable flow?
- What is the dependability of 300 m3/s?
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Assume 80% efficiency and 100m head available for hydropower generation.
Q.2
(a) Distinguish between [04]
- Field Capacity, permanent wilting point and Available water for the crop
- F-index and W-index.
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(b) There are 6 raingauge stations available to calculate the rainfall characteristics of a catchment whose shape can be approximately described by straight lines joining the following coordinates (distances in kilometers): (30,0), (80,10), (110,30), (140,90), (130,115), (40,110),(15,60): Coordinates of the raingauge stations and annual rainfall recorded in them in the year 2011 are given below: [10]
| Station | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|
| Co-ordinates | (40,50) | (50,0) | (90,30) | (90,90) | (90, 140) | (40,80) |
| Annual Rainfall (cm) | 156 | 136 | 128 | 102 | 85 | 128 |
Determine the average annual rainfall (areal mean precipitation) over the catchment using
- Thiessen mean method (Thiessen polygon method), and
- arithmetic mean method.
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Compare the methods based on the results obtained.
OR
(c) The mass curve of rainfall in a storm of total duration 270 minutes is given below: [10]
| Time since start in Minutes | 0 | 30 | 60 | 90 | 120 | 150 | 180 | 210 | 240 | 270 |
|---|---|---|---|---|---|---|---|---|---|---|
| Cumulative Rainfall (mm) | 0 | 6 | 18 | 21 | 36 | 43 | 49 | 52 | 53 | 54 |
- Draw the hyetograph of the storm at 30 minutes time step.
- Plot the maximum intensity-duration curve for this storm.
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Q.3
(a) List out the important assumptions made in the Unit Hydrograph (UH) Theory of modeling the effective rainfall-runoff process? [03]
(b) Enlist the various Recording types of Rain-gauges and Explain any one of them with a neat sketch? [04]
(c) The record of annual rainfall at station A covering a period of 22 years is given below: [07]
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| Year | Annual rainfall (mm) | Year | Annual rainfall (mm) |
|---|---|---|---|
| 1960 | 1300 | 1971 | 900 |
| 1961 | 840 | 1972 | 1020 |
| 1962 | 760 | 1973 | 1080 |
| 1963 | 890 | 1974 | 600 |
| 1964 | 1120 | 1975 | 750 |
| 1965 | 960 | 1976 | 1200 |
| 1966 | 800 | 1977 | 1600 |
| 1967 | 1250 | 1978 | 850 |
| 1968 | 1430 | 1979 | 1060 |
| 1969 | 890 | 1980 | 830 |
| 1970 | 780 | 1981 | 950 |
- Estimate the annual rainfall with return periods of 10 years and 50 years.
- What would be the probability of an annual rainfall of magnitude equal to or exceeding 1000 mm occurring at Station A?
- What is the 75% dependable annual rainfall at station A?
OR
Q.3
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(a) Discuss the factors that affect the evaporation from a water body? Explain the methods to reduce Evaporation Losses? [03]
(b) Discuss the current practice and status of rainfall recording in India? [04]
(c) The Infiltration capacity data obtained in a flooding type double ring infiltrometer test is given below: [07]
| Time since start (minutes) | 5 | 10 | 15 | 25 | 45 | 60 | 75 | 90 | 110 | 130 |
|---|---|---|---|---|---|---|---|---|---|---|
| Cumulative infiltration depth (cm) | 1.75 | 3.00 | 3.95 | 5.50 | 7.25 | 8.30 | 9.30 | 10.20 | 11.28 | 12.36 |
- Plot the cumulative infiltration vs time.
- Obtain the best values of the parameters in Green-Ampt’s equation to represent this data set.
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Q.4
(a) What is a Storm Hydrograph, mention its components with a neat sketch? [03]
(b) The infiltration capacity in a catchment is represented by Horton’s equation as fp = 3.0+e-2t Where fp is in cm/h and t is in hours. Assuming the infiltration to take place at capacity rates in a storm of 60 minutes duration. Estimate the depth of infiltration in 1) the first 30 minutes and ii) the second 30 minute of the storm. [04]
(c) Given a 2-hour Unit Hydrograph ordinates, find the 3- hour Unit Hydrograph for the catchment? Mention by which approach a 3-hour Unit Hydrograph would be constructed and what is the justification for the same? [07]
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| Time(Hours) | 0 | 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 22 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2-Hour UH(m3/s) | 0 | 20 | 60 | 150 | 120 | 90 | 70 | 50 | 32 | 20 | 10 | 0 |
OR
Q.4
(a) Define Perennial river, Intermittent river and Ephemeral river? [03]
(b) The infiltration capacity of soil in a small watershed was found to be 6 cm/h before a rainfall event. It was found to be 1.2 cm/h at the end of 8 hours of storm. If the total infiltration during the 8 hours period of storm was 15 cm, estimate the value of the decay coefficient Kf, in Horton’s infiltration capacity equation? [04]
(c) A storm with 10 cm of precipitation produced a direct runoff of 5.8 cm. The duration of the rainfall was 16 hours and its time distribution is given below. Estimate the F — index of the storm. [07]
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| Time from start (h) | 0 | 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 |
|---|---|---|---|---|---|---|---|---|---|
| Cumulative Rainfall (cm) | 0 | 0.4 | 1.3 | 2.8 | 5.1 | 6.9 | 8.5 | 9.5 | 10 |
Q.5
(a) Define Crop Period, Duty and Delta in terms of Irrigation water demand? [03]
(b) What is Duty? Derive a relationship between Duty and Delta? [04]
(c) Wheat is sown in an area in the Indo-Gangetic plain in the beginning of December and is harvested after four months, in the beginning of April. The reference evapotranspiration for these months are estimated as: December: 2.3 mm/d, January: 2.5 mm/d, February: 3.0 mm/d, and March: 5.9 mm/d. Estimate the total water requirement (delta), using the crop factor method, and compare with the delta from Table 2 (Given in Appendix). Also compute the duty of canal water? Refer to Table 1 given in Appendix for crop factor for different stages of Wheat growth? [07]
OR
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Q.5
(a) Define: Base Period, Kor Period and Culturable Command Area in terms of Irrigation water demand? [03]
(b) Describe the use of flow mass curve to estimate the storage requirement of a reservoir to meet a specific demand pattern. What are the limitations of flow mass curve? [04]
(c) A small catchment has an area of 68 ha and consists of Type-C soil. The land cover is 50% good condition parks, 10% commercial and business area, 30% residential, and 10% roads/paved areas. Assuming normal moisture conditions, determine the volume of direct runoff from a design storm of total rainfall of 200 mm from this catchment. What would be the values of runoff volumes if the past 5- day total rainfalls were 20mm and 60 mm, respectively, assuming growing season in the catchment? [07]
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Appendix
Table 1: Crop factor for different stages of growth
| Crop | Wheat | Potato | Tomato | |||
|---|---|---|---|---|---|---|
| Stage | Period (Days) | Crop Factor | Period (Days) | Crop Factor | Period (Days) | Crop Factor |
| Initial | 15 | 0.35 | 25-30 | 0.45 | 30-45 | 0.45 |
| Development | 25-30 | 0.75 | 30-35 | 0.75 | 40-45 | 0.75 |
| Mid-Season | 50-65 | 1.15 | 30-50 | 1.15 | 40-70 | 1.15 |
| Late-season | 30-40 | 0.45 | 20-30 | 0.85 | 25-30 | 0.80 |
| Total | 120-150 | - | 105-145 | - | 135-180 | - |
Table 2: Water requirement of some crops
| Crop | Base Period (days) | Delta (cm) | Kor Period (days) | Kor depth (cm) |
|---|---|---|---|---|
| Wheat | 120 | 40 | 28 | 12 |
| Rice | 120 | 125 | 20 | 30 |
| Potato | 105 | 75 | 25 | 25 |
| Sugarcane | 320 | 200 | 40 | 35 |
Table 3: AMC Classification in SCS-CN Method
| AMC Type | Cumulative rainfall over past five days (mm) | |
|---|---|---|
| Dormant Season | Growing Season | |
| I | <13 | <36 |
| II | 13 to 28 | 36 to 53 |
| III | >28 | >53 |
Some Important relationships:
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- S = 254 (1000/CN - 10)
- ER = (P-Ia)2 / (P+S)
- CN(I) = (4.2CN(II)) / (10-0.058CN(II))
- CN(III) = (23CN(II)) / (10+0.13CN(II))
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