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J12HYD-E1

The University of Nottingham DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL ENGINEERING A LEVEL 2 MODULE, AUTUMN SEMESTER 2012-2013 HYDROLOGY AND HYDROGEOLOGY Time allowed TWO Hours

Candidates may complete the front cover of their answer book and sign their desk card but must NOT write anything else until the start of the examination period is announced Answer ALL questions Only silent, self contained calculators with a Single-Line Display or Dual-Line Display are permitted in this examination. Dictionaries are not allowed with one exception. Those whose first language is not English may use a standard translation dictionary to translate between that language and English provided that neither language is the subject of this examination. Subject specific translation dictionaries are not permitted. No electronic devices capable of storing and retrieving text, including electronic dictionaries, may be used. DO NOT turn examination paper over until instructed to do so

ADDITIONAL MATERIAL:

Handout for Question 5(a)

INFORMATION FOR INVIGILATORS: Question papers should be collected in at the end of the exam – do not allow candidates to take copies from the exam room.

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2 J12HYD-E1 Please define the symbols and state clearly the units when answering the following questions

1.

2.

Sketch a hydrologic cycle and indicate in the sketch the major components of the hydrologic cycle.

(a)

[10]

The historical data at Lake Hefner indicates that the rate of evaporation can be well estimated using the following equation: The rate of water evaporation (mm per day) = N x u x (es-ed) where:

u is the wind speed at 2 m above the water surface in m s-1 es is the saturation vapour pressure at the water surface temperature in mb ed is the vapour pressure of air in mb N is the empirical mass transfer coefficient used to estimate evaporation and N=0.291/A0.05, where A is the surface area in km2

You are provided with the following data: ฀ ฀

฀ ฀

(b)

(c)

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Surface area of the Lake (A) = 10 km2 The saturation vapour pressure at the average water surface temperature (es) = 17 mb The average vapour pressure of the air above the reservoir (ed) = 13 mb The average wind speed above the water surface (u) = 20 km per hr

Estimate the annual evaporation from the surface of a reservoir.

[6]

You are working as a hydrologist in a city with high water demand. List three measures that may be used to help minimising evaporation.

[3]

Give three methods to estimate areal precipitation and comment on the accuracy.

[6]

3 J12HYD-E1

3.

(a)

Explain how a weir may be used to measure the flow rate in a stream.

[6]

(b)

The annual record of peak flood flows for a river is presented in Table 1. Determine the mean and standard deviation for the given data set.

[6]

Table 1: the annual record of peak flood flows for a river

(c)

Month

Day

Year

Dec Apr Sep Apr Dec Jan Mar Mar Apr Apr Feb Apr Apr Dec Feb Mar Mar Jul Mar Mar Jan

31 18 21 28 24 19 24 8 17 9 26 24 13 25 23 13 15 31 4 19 31

1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992

The Weibull equation is now a commonly used formula to estimate the probability for unspecified distributions. The equation states that the probability of values being equal to or larger than the ranked value can be estimated as:

P where:

(d)

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Flow rate (m3 s-1) 43 547 125 259 200 218 186 155 233 82 102 269 414 113 385 271 204 68 129 377 64

m n฀ 1

n = the number of records m = the rank of descending values

Basing on the data set in Table 1, estimate the once in five years flood.

[8]

The design capacity of a river dam is 400 m3 s-1. Estimate the risk of the flooding in the next five years based on the data set given in Table 1.

[5]

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4 J12HYD-E1

4.

(a)

(b)

5.

(a)

(b)

Explain the following hydrological terms (a) catchment (b) watershed (b) drainage basin (d) divide.

[6]

List four descriptive parameters that may be used to describe watershed characteristics.

[4]

The height of the water table (in metres) in three boreholes is shown in the map below. Determine the hydraulic head gradient, and plot on the SEPARATE HANDOUT SHEET the direction of groundwater flow.

[10]

Two water reservoirs are situated 45 metres apart. The water level in both reservoirs remains constant with the water level in reservoir B being 17 metres lower than reservoir A. A sandstone horizon intercepts both reservoirs. The properties of the sandstone horizon are: Thickness = 5 metres Porosity = 12% Permeability k = 2 X 10-3 metres per sec

(c)

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Use Darcy’s law to calculate the volumetric water flow rate per unit width within the sandstone aquifer.

[5]

Following part (b), the water in reservoir A may be contaminated. Use the volumetric flow rate determined in part a) to calculate the time taken for a trace of the contaminant to first appear in reservoir B following a contamination event in reservoir A.

[5]

5 J12HYD-E1 6.

(a)

The flow rate to a well through an unconfined aquifer under steady condition (Q = flow rate, R = distance of monitoring wells from pumping well, H height of water table, k = aquifer permeability) can be found as:

Q

k

 H H  2 2   ln R2 R 1

The flow rate to a well through an unconfined aquifer under steady condition (Q = flow rate, R = distance of monitoring wells from pumping well, H = height of water table, m = aquifer thickness, k = aquifer permeability) can be determined as:

  k   2  m H 2   H1 Q     ln R2 R 1 A confined artesian aquifer is being pumped by a fully penetrating well to determine its permeability. The equilibrium flow rate is recorded as 454 m3 per hr. The thickness of the aquifer is 100 ft. The drawdown in observation wells is noted as 3 ft and 9 ft at distances 100 ft and 10 ft, respectively, from the pumped well. Calculate the permeability of the aquifer (1 ft = 0.3048 metre). [10]

(b)

Explain hydrostatic equilibrium developed along coastal areas, and how excessive groundwater pumping may cause salt water intrusion and contamination of an aquifer. You are encouraged to use diagrams to illustrate your answer.

[10]

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END

J12HYD-E1 Handout for Question 5

5.

The height of the water table in metres in three boreholes is shown in the map below. Calculate the hydraulic head gradient and the direction of flow

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[10]...