488 HYDROLOGY
intensities. Storm patterns, durations, and movements can be
studied. The storm movement can be crucial for a large river
for it is not unknown for storms to move downstream at a
rate similar to the fl ood wave movement, so that consider-
able reinforcement of the fl ood can take place. On northern
rivers like the Mackenzie, which fl ows to the north, snow-
melt and ice breakup occur from south to north, resulting in
build up of ice jams and fl oods. There is also the question of
combination of rare events such as rain on snow or several
consecutive storms. Concerning rain on snow, it is notice-
able that the snow-covered areas are the ones which mainly
contribute to run-off, probably because the snowmelt has
already primed the soil and also because the 100% humidity
of the warm air during rain can produce considerable con-
densation melt.
The calculation of fl ood run-off from such storm or melt
patterns requires a run-off simulation calculation of the type
previously discussed. The resulting fl ood fl ow may be modi-
fi ed by the reservoir storage until maximum permissible
reservoir stage is reached. From then on the spillway must
be capable of passing the total fl ood, less any fl ow passed
through the turbines or diverted to irrigation.
A third approach, which is often of comfort to the
designer, is to compare the design fl ood with that used
on other similar rivers. Careful comparison and cross-
correlation may help to confi rm the reasonableness of the
fi nal design values.
Standard project fl oods^1 can be determined by simi-
lar processes and used for the design of other aspects of a
scheme, such as downstream diking and channel protection
schemes. In this case the resulting damage from failure may
not be so widespread and may not endanger life. It is not
unusual for such design fl oods to be only a fraction of the
value of a spillway design fl ood, perhaps half.Complex SystemsUsually a complex water resource system involves the oper-
ation of storage or even several storages. Such operation
aims to minimize fl ood risk at one extreme and drought risk
at the other end of the scale. The scheme must satisfy vari-
ous complex demands for such uses as hydro-power, irriga-
tion, fi sheries requirements, water supply, water quality, and
navigation. Recreation is also now a demand of increasing
importance and imposes limitations regarding water levels
on beaches or in marinas. Water intakes and wastewater
effl uent lines set additional limitations. Water quality also
sets demands on minimum fl ows, water temperature, lake
levels, etc.
An important aspect of river basin behavior which has
long been neglected is the effect of the alteration of run-
off pattern on the ecological balance and erosion patterns
downstream. Hydrological studies can supply the biologi-
cal ecologists with information on how fl ood levels and
seasonal run-off patterns will change with given schemes
so that harmful effects can be recognized before damage
is done.Added to this complexity is the question of run-off fore-
cast accuracy which can greatly infl uence the effi ciency of
water utilization. In the evaluation of such schemes hydrology
is seen in its most necessary and challenging role. The hydrol-
ogist is called on to develop accurate forecasts of run-off. He
also must simulate the total system behavior and then subject
the system to sequences of run-off patterns generated from the
characteristics of the recorded data. The resulting performance
of the system is then analyzed from the economic viewpoint
and, frequently, projections must be made into the future to
estimate eventual demands and trends and system capability.
In this type of problem the whole technical capability of the
hydrologist is utilized and as techniques and data improve so
the confl icting requirements of water use, water quality, recre-
ation, and fl ood control can be better reconciled.REFERENCESTextbooks and Reference Books- Chow, V.T., Handbook of Hydrology, McGraw-Hill.
- Linsley, Kohler, and Paulhus, Hydrology for Engineers, McGraw-Hill.
- Bruce, and Clark, Introduction to Hydrometeorology, Pergamon.
- Henderson, Open Channel Flow, MacMillan.
- Viessman, Knapp, Lewis and Harbaugh, Introduction to Hydrology,
2nd Edition, IEP Series, Dun-Donnelley, 1977. - Meinzer (Ed.), Hydrology, Dover.
- Maas et al., Design of Water Resource Systems, Harvard.
Statistics- Moroney, M.J., Facts from Figures, Pelican.
- Parl, B., Basic Statistics, Doubleday College Courses, Refs. 1,2,3.
- Kendall, M.G., A Course in Multivariate Analysis.
- Fisher, and Tippett, Limiting forms of the frequency distribution, Cam-
bridge Phil. Soc., Vol 24, 1927–28. - Gumbel, Applications of extreme statistics, lecture 4, applied math-
ematics series 33, U.S. Nat. Bureau of Standards. - Matalas, N.C., and M.A. Benson, Effect of interstation correlation on
regression analysis. J. of Geophys. Res., 66 , No. 10, pp. 3285–3293,
Oct. 1961. - Snyder, W.M., Some possibilities for multivariate analysis in hydrolog-
ical studies, J. of Geophys. Res., 67 , No. 2, pp. 721–729, Feb. 1962. - Wallis, J.R., Multivariate statistical methods in hydrology—A com-
parison using data of known functional relationship. Water Resources
Research, 1 , No. 4, pp. 447–461, 1965.
Runoff- Sherman, L.K., Streamflow from rainfall by the unit-graph method,
Eng. News. Rec., 108 , pp. 501–505, April 7, 1932. - Nash, J.E., The form of the instantaneous unit hydrograph, Intern.
Assoc. of Sci. Hydrology, Pub. 45, 3 , pp. 114–121, 1957. - Dooge, J.C.I., A general theory of the unit hydrograph, J. Geophys.
Research, 64 , No. 1, pp. 241–256, 1959. - Singh, K.P., A non-linear approach to the instantaneous unit hydro-
graph, Ph.D. thesis, University of Illinois, 1962. - Snyder, W.M., Hydrologic Studies by electronic computers in TVA,
Proc. A.S.C.E. HY 2, pp. 1–10, Febr. 1960. - Snyder, W.M., Matrix operations in hydrograph computations, Tennes-
see Valley Authority, Res. Paper No. 1, 10 pages, Knoxville, Tennessee,
Dec. 1961. - Laurenson, E.M., Storage analysis and flood routing in long river
reaches, J. Geophys. Res., 64 , No. 12, pp. 2423–31, Dec. 1969.
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