Episodic Increases In Stream Acidity, Catchment Flow Pathways And Hydrograph Separation
type: CreativeWork
description: A positive correlation between stream discharge and stream acidity is common in areas affected by Surface Water Acidification (SWA). This has led to conceptual models of SWA in which low flow is less acid because of slow weathering reactions during a long transit time through the catchment. Acid storm runoff was considered to be primarily precipitation routed through the catchment too rapidly for weathering to occur. The predictions of SWA models are sensitive to the proportions of short and long transit time water reaching the stream. Those proportions, however, are poorly defined by the rainfall and runoff data customarily used to calibrate hydrological models. Isotope Hydrograph Separation (IHS) divides storm runoff into components of new rainwater and "pre-event water" which was in the catchment prior to a storm event. Such data can be used to improve the calibration of SWA model hydrology, but IHS usually shows pre-event water rather than precipitation to be the major component of storm runoff. If IHS is correct, then models of SWA need to be revised to include a larger proportion of pre-event water in acid storm runoff. This may alter the predictions of SWA models significantly. Doubts about the validity of IHS, though, made it unclear whether that revision was warranted. IHS is based on several assumptions, one of which is that pre-event water can be assigned a single, static δ18O value. The possibility of spatial variability in the δ18O of pre- event water, coupled with changing flow pathways during the storm hydrograph, made that assumption questionable. The rapidity with which stream discharge and chemistry react to rainfall could also be taken to suggest that IHS overestimates the component of pre-event water in the storm hydrograph. This thesis seeks to test whether the results of IHS are adequate grounds for revising the hydrological concepts upon which the understanding of SWA is based. Using detailed field investigations at Loch Fleet in Scotland and …
abstract: A positive correlation between stream discharge and stream acidity is common in areas affected by Surface Water Acidification (SWA). This has led to conceptual models of SWA in which low flow is less acid because of slow weathering reactions during a long transit time through the catchment. Acid storm runoff was considered to be primarily precipitation routed through the catchment too rapidly for weathering to occur. The predictions of SWA models are sensitive to the proportions of short and long transit time water reaching the stream. Those proportions, however, are poorly defined by the rainfall and runoff data customarily used to calibrate hydrological models. Isotope Hydrograph Separation (IHS) divides storm runoff into components of new rainwater and "pre-event water" which was in the catchment prior to a storm event. Such data can be used to improve the calibration of SWA model hydrology, but IHS usually shows pre-event water rather than precipitation to be the major component of storm runoff. If IHS is correct, then models of SWA need to be revised to include a larger proportion of pre-event water in acid storm runoff. This may alter the predictions of SWA models significantly. Doubts about the validity of IHS, though, made it unclear whether that revision was warranted. IHS is based on several assumptions, one of which is that pre-event water can be assigned a single, static δ18O value. The possibility of spatial variability in the δ18O of pre- event water, coupled with changing flow pathways during the storm hydrograph, made that assumption questionable. The rapidity with which stream discharge and chemistry react to rainfall could also be taken to suggest that IHS overestimates the component of pre-event water in the storm hydrograph. This thesis seeks to test whether the results of IHS are adequate grounds for revising the hydrological concepts upon which the understanding of SWA is based. Using detailed field investigations at Loch Fleet in Scotland and …
author: Bishop, Kevin Harold
license: https://www.repository.cam.ac.uk/bitstreams/c3adcf34-3f41-493b-a9f6-4e354ecb5e3e/download
license: http://purl.org/NET/rdflicense/allrightsreserved/
date published: 1991-10-31
date modified: 2026-07-22T22:24:18Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.120776