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presented. In common with the Ed50 data in Table 3.3, the generally negative correlation coefficients are indicative of a systematic intra-storm trend, rather than a random variation through the hydrograph.

Mann-Whitney U-test analysis of the statistical significance of the intra-storm variability in the EPSD is summarized in Table 3.5. Using this test it is possible to identify if the EPSD of replicate measurements from two sample sets have been taken from a common statistical population. Accordingly, for each storm event, comparisons were made between the values of the mean and median EPS, as well as the degree of sorting for all possible pairs of the replicate sample sets comprising the periodic intra-storm deployments of the Par-Tec equipment. The data presented in Table 3.5 demonstrate that, for all the study sites, the EPSD measured during each periodic intra-storm deployment was in the majority of cases statistically significantly different in all three tested parameters from the EPSD measured during the remaining periodic deployments in the storm event.

3.4.4 Inter-Storm and Seasonal Variability in the EPSD and Associated DOA

From the data presented in Table 3.2 it is evident that there is significant inter-storm variability of both the EPSD and DOA of fluvial suspended sediment in the study area. At every study site, each storm event is characterized by a unique mean storm-period value of Ed5o, and intra-storm range in Ed5o and DOA, with an inter-storm range in the mean storm-period Ed50 of between 4.1 xm (Upper Exe) and 29.4 xm (Culm). Similarly, with only one exception (R. Culm 13/09/93 and 25/05/94), the mean storm-period value of the DOA is unique to each event, with an inter-storm range of between 14.4% (Upper Exe) and 66.3% (Culm).

Mann-Whitney U-test analysis of the statistical significance of the inter-storm variability in the EPSD is summarized in Table 3.6. For each study site, all possible comparisons were made between the intra-storm periodic data sets for the mean

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