Hydro Essay

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HYDROLOGY BEng (Hons) Civil Engineering May 2012 ASSIGNMENT 1 (Chapter 1 & 2) 1) A catchment area of 140 km2 received 120 cm of rainfall in a year. At the outlet of the catchment the flow in the stream draining the catchment was found to have an average rate of 2.0 m3/s for 3 months, 3.0 m3/s for 6 months and 5.0 m3/s for 3 months. a) What is the runoff coefficient of the catchment? b) If the afforestation of the catchrnent reduces the runoff coefficient to 0.50, what is the increase in the abstraction from precipitation due to infiltration, evaporation and transpiration, for the same annual rainfall of 120 cm? 2) Estimate the constant rate of withdrawal from a 1375-ha reservoir in a month of 30 days during which the reservoir level dropped by 0.75 m in spite of an average inflow into the reservoir of 0.5 Mm3/day. During the month the average seepage loss from the reservoir was 2.5 cm, total precipitation on the reservoir was 18.5 cm and the total evaporation was 9.5 cm. 3) A catchment has four sub-areas. The annual precipitation and evaporation from each of the sub-areas are given below: Sub-area | Area (Mm2) | Annual precipitation (mm) | Annual evaporation (mm) | A | 10.7 | 1030 | 530 | B | 3.0 | 830 | 438 | C | 8.2 | 900 | 430 | D | 17.0 | 1300 | 600 | Assume that there is no change in the groundwater storage on an annual basis and calculate for the whole catchment the values of annual average: (i) precipitation, and (ii) evaporation. What are the annual runoff coefficients for the sub-areas and for the total catchment taken as a whole? 4) A catchment area has seven raingauge stations. In a year the annual rainfall recorded by the gauges are as follows: Station | P | Q | R | S | T | U | V | Rainfall (cm) | 130.0 | 142.1 | 118.2 | 108.5 | 165.2 | 102.1 | 146.9 | For a 5% error in the

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