Date of Award

1-1-2016

Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy

Department

Civil, Structural, & Environmental Engineering

Second Advisor

Dr Joseph Harrington

Third Advisor

Dr Jerry Murphy

Abstract

This thesis presents the results of new and original research on suspended sediment (SS) and nutrient concentrations and loads on the Rivers Bandon and Owenabue in the south of Ireland. It addresses the knowledge gap in SS and nutrient concentration data and in particular SS load/yield estimation methods. A comprehensive database of SS and nutrient concentrations has been established. An investigation into the relationship between water discharge and sediment and nutrient transport is presented and new original relationships between turbidity and suspended sediment concentration (SSC) and nutrients are developed. Turbidity-based suspended sediment loads (SSL) are estimated from the continuous turbidity record using the developed relationships with annual loads of 9.7 tonnes per square kilometre per year (t km‘‘ year’') and 18 t km'^ year ' estimated for the Rivers Bandon and Owenabue, respectively. Rating curves are developed to assess their accuracy compared to the turbidity-based SSL for the first time in an Irish context. Generally, rising stage and winter rating curves explain the variation in sediment concentration well (r‘ > 0.4), but winter and falling stage curves are not a good fit. Rating curves are shown to provide acceptable estimates of SSL at the large (annual) scale on both rivers, without the need for stage or seasonal rating curve separation. The variation in SSC between and within storm events is found to be large and over 73% of the total annual load is transported when flows are above the 10% exceedance flow rate on both rivers, indicating that stonn-based events are critical to load delivery. The sediment associated nutrient transport in the two rivers is also examined, with brief surges in particulate forms of nitrogen and phosphorus observed at the onset of the events analysed. These are accompanied by decreases in the dissolved forms of the monitored nutrients. Turbidity is used as a surrogate for phosphorus concentrations, as it correlates well with most of phosphorus species concentrations. Nitrogen does not correlate well with turbidity or SSC, and loads are estimated using an averaging estimator (interpolation). The particulate fraction of nutrient transport is found to be 25% and 35% of the respective total nitrogen and total phosphorus yields on the River Bandon, and 41% and 52% on the River Owenabue. The total portion of SSL consisting of particulate nutrients is estimated to be in excess of 10% on both the River Bandon and the River Owenabue.

Access Level

info:eu-repo/semantics/openAccess

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