Lag Time and Hydrograph Form in the Upper Feshie Catchment

Abstract

This study presents findings relating to the hydrological response of the Lower Eidart and the Upper Feshie which are neighbouring sub-catchments of the Feshie catchment. These catchments have contrasting physical characteristics where the Lower Eidart has >59% mineral soil and >27% blanket peat which contrast with the Upper Feshie which has >65% blanket peat and a further 10% peaty soil.

The Vbar method has been used to calibrate the stage-discharge rating equation at the outlet of each of these gauged catchments beyond current empirical gaugings. The extended rating curve applied to a year of continuous time series gauge data to compare the hydrological response of these catchments.

Analysis of lag time to peak discharge found that the Lower Eidart catchment peaked 23 minutes sooner than the Upper Feshie, which is statistically insignificant based on a Mann-Whitney Wilcoxon Test of Difference (P= 0.1171). It was also found that both the Lower Eidart and Upper Feshie have a remarkably similar hydrological response to both frontal and convective rainfall based on the creation of a median hydrograph for these catchments. Lower Eidart was found to have a higher antecedent flow prior to the synthesised median hydrograph. The higher antecedent flow may contribute to the lower peak discharge observed in the time series (11.8 m³/s) when compared with Upper Feshie which had a peak discharge of 20.2 m³/s. The higher baseflow observed in the time series is consistent with existing literature in the area, however, is contradictory to the Bfihost estimation found in the FEH catchment descriptors.

The Vbar method may be applicable to other upland catchments where empirical gauging data is sparse, in the context of water management and monitoring, especially where manual gaugings are not safe at higher flows.

Date of Award	2022
Original language	English
Awarding Institution	University of Dundee
Supervisor	Andrew Black (Supervisor)