24. Read the texts again and make notes under the following headings. Then use your notes to talk about hydrology.

1. Hydrology as a scientific discipline.

2. Hydrologic (water) cycle.

3. Subsurface water.

4. The work of hydrologists.

UNIT III RESERVOIRS

1. Complete the sentences with the words from the list below.

useful storage, the water-surface profile, storage capacity, dead storage, inflow

1) _______ is the most important physical characteristic of any reservoir.

2) _______ is the storage volume between the minimum and normal pool levels.

3) _______ is water held below minimum pool level.

4) The computation of the _______ provides information on the water level at various points.

5) Yield may vary from year to year and is dependent upon _______ .

2. Find the translation of the following terms and memorize their meaning.

channel	relation
(in)variable	storage reservoir
to effect	conservation reservoir
a stock tank	distribution reservoir
to determine	computation
permeable	pressure grouting
run-off	multipurpose
firm yield	fractured rock
safe yield	pool level
to increase	to flow out
to seal	natural conditions
inflow	to flood
to meet the requirements	consumer
water-surface profile	to create
pond	storage
dead storage	to conserve
useful storage	to occur
storage capacity	useful life
leakage	constant

3. Read the text to get the gist of it. Answer the following questions.

a) Do the main functions of reservoirs depend on their sizes?

b) What should the reservoir’s banks be made of?

Text A

D

Picture 1 (The Jung Hua Dam on the Da Han River in Taoyuan Country, Taiwan)

ams are built in the river channels to create reservoirs for storing water. Rivers in natural conditions never carry a constant amount of water. In dry summer and in winter it is very small but in spring the water in the rivers is so high that it flows out of the rivers and floods their banks, whereas water consumers require a constant amount of water invariable during the whole year. To meet these requirements the run-off of the rivers must be controlled. The control of the river run-off can be effected by creating a reservoir. There are some types of the reservoirs: storage (conservation) reservoirs and distribution reservoirs. Stock tanks or small ponds may also conserve water. Whatever the size of the reservoir, its main functions are to regulate the flow of water and to provide storage of water, their most important physical characteristic being storage capacity.

Capacity of reservoirs constructed in natural conditions must usually be determined from topographic surveys.

T

Picture 2 (Gelmersee reservoir in Switzerland)

he storage volume between the minimum and normal pool levels is called the useful storage. Water held below minimum pool level is dead storage. In multipurpose reservoirs the useful storage may be subdivided into conservation storage and flood-control storage. Reservoir banks are usually permeable and water enters the soil when the reservoir fills and drains out as the water level is lowered. This bank storage effectively increases the capacity of the reservoir. But if the walls of the reservoir are of badly fractured rock, permeable volcanic material or limestone, serious leakage may occur. This leakage may result in a loss of water. If leakage occurs through a few channels or within a small area of fractured rock, then it is quite possible to seal this area by pressure grouting. If the area of leakage is large the cost of grouting may be too great.

The computation of the water-surface profile is an important part of reservoir design since it provides information on the water level at various points along the length of the reservoir.

Docks, houses, roads and bridges along the banks of the reservoir must be located above the water level.

Probably the most important aspect of storage-reservoir design is an analysis of the relation between yield and capacity. Yield is dependent upon inflow and it may vary from year to year. Most water-storage reservoir must have safe and firm yield, i.e. the maximum quantity of water which can be guaranteed during a critical dry period.