UNIT – II
ABSTRACTION FROM PRECIPITATION 16. Write short note on rainfall hyetograph.
The instantaneous rainfall intensity is usually denoted by (i) and expressed in mm/ hrs. A graph showing the variation of rainfall intensity with time is called a rainfall hyetograph.
17. Define rainfall mass curve.
A graph showing the cumulative depth of rainfall against time is known as the rainfall mass curve. 18.Define point rainfall or station rainfall.
The rainfall obtained from a single rain gauge station is known as the point rainfall or station rainfall 19.Define Normal rainfall
The normal rainfall is the average value of rainfall at a particular date, month or year over a specified 30 year period. It is recomputed every decade.
20.What is a DAD curve ?
The average depth of rainfall are plotted against the areas up to the encompassing Isohyets. The curves of maximum depth verses area , with duration are called DAD curves.
21.Define PMP.
It has been defined as that depth of precipitation which for a given area and duration can be reached but not exceeded under known meteorological conditions.
22.List out the methods available for estimating missing data. i. Interpolation from isohyetal maps.
ii. Arithmetic average method. iii. Normal ratio method. iv. Inverse distance method. v. Regression method.
23.Write down the approaches used for estimating the PMP. Basically two approaches are used for estimating the PMP. They are i. Meteorological Methods
ii. The statistical study of rainfall data.
24.Explain W index
This is refined version of o index. It includes depression storage and interception from total losses. It is the average infiltrating rate during the time rainfall intensity exceeds the capacity rate.
W = P – Q – S / tf where W = Average rate of infiltration P = Total storm rainfall
Q = Total storm runoff
S = Volume of depression storage
Tf = Total time during which rainfall intensity is greater than W
25.What is an infiltrating capacity curve?
The infiltrating rates are plotted against their time intervals as a bar diagram.By joining the mid points of the bars we get the approximate infiltration capacity curv
26. Define Transpiration ratio?
Transpiration ratio = Weight of water transpired / Weight of dry matter produced The average value of transpiration ratio being 700
I = Inflow
UNIT – III
HYDROGRAPHS 1. Define runoff?
The portion of the precipitation which appears in the surface either perennial or intermittent in nature is called runoff. The unit of runoff is cumecs.
2. Enlist the components of runoff?
i) Channel precipitation ii) Direct runoff iii) Overland flow iv) Base flow v) Inter flow
3. What is direct runoff?
That part of the runoff which enters the stream immediately after precipitation 4. Explain base flow
The flow reaches a stream essentially as ground water flow is called base flow. 5. What is perennial stream.
A perennial stream is one which always carries some flow. There is considerably some amount of groundwater throughout the layer.
6. What is an ephemeral stream?
A stream which becomes dry soon after the end of the precipitation. There will not be any base flow contribution.
7. What is meant by precipitation excess?
That part of precipitation which contributes directly to the surface runoff. 8. Define a flow mass curve?
It is the plot of cumulative discharge volume against time plotted in chronological order. 9. Define basin lag(Time lag)
Basin lag is defined as the time from the center of rainfall to the hydrograph peak. 10. What are the basic assumptions of unit hydrograph theory?
(i) the time invariance (ii) The linear response
11. Write short notes on drainage density?
Drainage density = Length of the channel / Area of the basin 12. Define hydrograph?
It is a graph drawn between discharge against time. It consists of direct runoff and base flow. 13. Define unit hydrograph?
It is defined as the hydrograph if direct runoff resulting from an isolated rainfall of unit duration occurring uniformly over the basin and produces unit runoff.
14. What are the methods to determine the unit hydrograph? Unit hydrograph developed by the following two methods i) Method of Super position ii) S-curve technique
15. Write short notes on method of super position?
If a D-h unit hydrograph is available and it is easy to develop hydrographs of nD-h where n is an integer. It is easily accomplished by superimposing n-unit hydrograph with each separated from the previous on D-h.
16. Define S-curve technique?
It is a curve obtained from the summation of infinite series of D-h unit hydrograph spaced by D-h apart. A smooth curve is obtained resulting to S shape curve called S-curve hydrograph.
17. Define Synthetic unit hydrograph?
Unit hydrographs derived from empirical equations are called synthetic unit hydrograph. The following three parameters are used for development of synthetic unit hydrograph.
18. Define instantaneous unit hydrograph?
If the duration of effective rainfall approaches zero, the unit hydrograph may be called as instantaneous unit hydrograph.
19. What are all the applications of unit hydrograph?
i) Once unit hydrograph is developed for a basin and it can be used to obtain direct runoff hydrograph for any storm event on the basin.
ii) If the unit hydrograph is applied to max. probable precipitation on the basin, then the max. probable precipitation is obtained.
20. What are all the advantages of instantaneous unit hydrograph over direct unit hydrograph?
i) The advantage of IUH over DUH is that it eliminates the problem of unit duration and the restriction of uniform distribution of rainfall in time.
ii) The use of IUH is better suited for the needs of theoretical investigations on the rainfall-runoff relationship.
21. Define stream density?
The stream density of a basin is expressed as the no.of streams per sq.km. 22. Define drainage density?
It is expressed as the total length of all stream channels per unit area of the basin. 23. Define concentration time?
The time required for the falling rain at the most distant point in a drainage area to reach stream outlet is called concentration time.
24. Define overland flow?
When a storm occurs, a portion of rainfall infiltrates in to the ground and some portion may
evaporate. The rest flows as a thin sheet of water over the land surface which is termed as overland flow.
25. Define effective precipitation?
The part of the precipitation that contributes entirely to the direct runoff may be called effective precipitation or effective raindfall
26. Define isochrones?
The line joining the points of equal travel time of rainfall is called isochrones. It is helpful in deriving hydrographs.
27. State Virgin flow?
It is a stream flow which is unaffected by the artificial diversions, storage or other works of man in or on the stream channels.
28. Define surface runoff?
It is the part of runoff which travels over the ground surface through channel to reach the basin outlet.
29. Define subsurface runoff?
PART B
What are the diffident procedures used for the base flow separation?
6. What do you understand by unit hydrograph? How is it derived? Explain its use in construction of flood hydrograph resulting from two or more periods of rainfall
Explain briefly about the O - Index and W - Index.