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TitleHydrology in Practice
TagsSun Atmosphere Of Earth Evaporation Atmosphere Water Vapor
File Size14.5 MB
Total Pages628
Table of Contents
                            Book Cover
Preface to the Second Edition
Preface to the Third Edition
1. The Hydrological Cycle, Hydrometeorology and Climate
2. Hydrometric Networks and Catchment Morphometry
3. Precipitation
4. Evaporation
5. Soil Moisture
6. River Flow
7. Groundwater
8. Water Quality
9. Data Processing
10. Precipitation Analysis
11. Evaporation Calculations
12. River Flow Analysis
13. Rainfall-Runoff Relationships
14. Catchment Modelling
15. Stochastic Hydrology
16. Flood Routing
17. Design Floods
18. Urban Hydrology
19. Water Resources
20. River Basin Management
Appendix—Statistical Formulae
Author Index
Subject Index
Document Text Contents
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Page 314

UK only a 150 m3s 1 peak may be expected from the same drainage area. (The Findhorn
record in Scotland would not be worth plotting on the USA graph!) Thus, when making a
general appraisal of peak records, such a relationship of peak discharge to catchment area
should be made according to climatic region. The USA has been divided into 17 flood
regions (Crippen and Bue, 1977), and such subdivisions in the UK have been made for
more detailed studies of flood events (NERC, 1975). A world-wide relationship between
maximum floods and catchment area has been published by Rodier and Roche, 1984
(Fig. 12.4(b)).

Some hydrologists prefer to convert the absolute peak discharges into relative values
per unit area for plotting against catchment area, thus giving

Fig. 12.4 (a) Maximum flood

River flow analysis 299

Page 315

Fig. 12.4 (b)

an inverse relationship and a declining curve with increased catchment area. Sample
values from the UK are shown in Table 12.3. These have been taken from Boorman et al.
(1990). They demonstrate the contrast between the exceptional discharges from small
areas (<10 km2) evaluated after the events and the peak flows at formal river gauging

Numerous empirical formulae given in the hydrological literature have been derived
from the relationship between peak discharges and catchment areas, with the coefficients
specifically determined for particular countries or climatic regions. In attempting to use
such formulae to obtain peaks for ungauged catchments, the hydrologist must guard
against applying them to inappropriate conditions and areas.

12.2 River Regimes

In Table 12.1, the monthly mean discharges for the River Thames in 1973 exhibit a
distinctive seasonal pattern, with the highest values occurring in the winter months. The
expected pattern of river flow during a year is known as the river regime. (This term may
also be applied to the absolute range of flow in a river and has been used in outdated flow
theories.) Flow records for 20–30 years are required to provide a representative pattern,
since there may be considerable variations in the seasonal discharges from year to year.
The averages of the monthly mean discharges over the years of record calculated for each
month, January to December, give the general or expected pattern, the flow regime of the

Hydrology in practice 300

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