Analysis of Regional Flood Frequency on the Nene and the Great Ouse

Although the series of gauging records for British rivers are neither numerous Lnor (with few excepti ns) long, some f them appear adequate fo use n certain kinds of analysis. In particular, a preliminary study of the hydrometric statistics pub? lished in the ' Surface water year-books'1 indicates that flood-flow frequencies can be obtained for a region which includes large parts of two distinct river-systems. The region comprises 1811 square miles, of which 1180 are drained by the Great Ouse above Brownshill Staunch (grid reference 52/369727) and 631 by the Nene above Orton (grid reference 52/166972). Records from nine gauging-stations have been analysed to give the relationships between catchment area and flood-frequency for floods of recurrence-intervals up to 10 years. In this context, the term flood does not necessarily imply a discharge sufficient to inundate the floor of a valley, but merely means a high discharge. The floods discussed here are annual floods, i.e., the highest discharges in individual water years.2 The recurrence-interval is the average interval in which a flood of a given size (in units of discharge) will occur as an annual maximum. Thus the 5-year flood?the flood with a recurrence-interval of 5 years?can be expected to occur as the annual maximum once in a given 5-year period. Since not all the gauging-stations supply continuous records (Table I), it has been necessary to use records of maximum daily discharges; i.e., records of the highest mean daily discharges recorded in single years. Momentary peak discharges would be more to the purpose, but it will be shown that a simple relationship connects maximum daily and momentary peak discharges on the Nene, where a correcting factor can be employed. The techniques of analysis described in what follows are familiar to hydrologists and are standard practice in the U.S. Geological Survey.3 They include (1) the adjust? ment of available records to a base-period by interpolation of missing figures, (2) computation of recurrence-intervals for floods of given magnitudes at each station, (3) testing for homogeneity of records, and (4) graphing of the relationship of catch? ment area to floods of selected recurrence-interval for the region as a whole. 1. Adjustment of records to a base-period.?When some of the series of available records are short or broken (Table I), missing figures can be interpolated. Interpolated values have no reality, but interpolation is useful in making the actual records easy to handle, and is especially convenient when short series include both very high and very low annual floods. As will be shown, adjusted and unadjusted series give almost identical results, so that (in this instance at least) the increased convenience obtained by interpolation is not gained at the expense of accuracy. Interpolation is effected in the following manner: one station, normally a station with an unbroken record for the base-period, is selected as a station of reference; the highest annual discharges recorded at other stations are plotted, year for year, against the corresponding discharges at the station of reference; on each graph a line is drawn

Archaeology · Flood myth · Geography · Physical geography · Hydrology and Drought Analysis · Hydrology and Sediment Transport Processes · Hydrology and Watershed Management Studies

• George Harry Dury, 1916–1996

  Open Access•Trevor Langford–Smith•Australian Geographical Studies•1997

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• Some Results of a Magnitude‐frequency Analysis of Precipitation

  Open Access•G H Dury•Australian Geographical Studies•1964

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