Raymond Flynn - Academia.edu (original) (raw)

Papers by Raymond Flynn

Effective implementation of the Water Framework Directive requires a reappraisal of conventional ... more Effective implementation of the Water Framework Directive requires a reappraisal of conventional approaches to water quality monitoring. Quantifying the impact of domestic wastewater treatment systems (DWWTS) in Irish catchments is further complicated by high levels of natural heterogeneity. This paper presents a numerical model that couples attenuation to flow along different hydrological pathways contributing to river discharge; this permits estimation of the impact of DWWTS to overall nutrient fluxes under a range of geological conditions. Preliminary results suggest high levels of attenuation experienced before DWWTS effluent reaches bedrock play a significant role in reducing its ecological impact on aquatic receptors. Conversely, low levels of attenuation in systems discharging directly to surface water may affect water quality more significantly, particularly during prolonged dry periods in areas underlain by low productivity aquifers (>60% of Ireland), where dilution capacity is limited.

Biology and environment, 2016

Environmental Earth Sciences, Jun 13, 2023

European geosciences union general assembly, Apr 1, 2011

Environmental Earth Sciences, Apr 1, 2022

Research Square (Research Square), Dec 12, 2022

Across the Island of Ireland, hard rock aquifers which are found to underlie over 65% of Ireland ... more Across the Island of Ireland, hard rock aquifers which are found to underlie over 65% of Ireland (Robins and Misstear, 2000) are commonly referred to as poorly productive bedrock aquifers (PPA), characterised by low well yields (GSI, 2006). Despite their limited role in water supply, PPAs are found to contribute significantly to the maintenance of river baseflow levels, especially in upland catchments during sustained dry periods (Comte et al., 2012). Typically, these units are considered to be devoid of intrinsic matrix porosity: instead, the flow of groundwater is confined to secondary porosity generated through interconnected fractures and fissures. Previous studies have highlighted the challenges in characterising PPA systems due to the heterogeneity of geological structures at micrometre–metre (cf. Neuman, 2005) and regional scales (km to 10s km, cf. Krasny, 2002). This is particularly the case in hard rock environments where the permeability of bedrock is largely dictated by t...

Residential on-site wastewater treatment systems (OSWTS), where contaminated wastewater discharge... more Residential on-site wastewater treatment systems (OSWTS), where contaminated wastewater discharges to the subsurface, act as the dominant means of domestic wastewater disposal in rural Ireland; septic tanks constitute the most common technology employed. The objective of this study was to determine the effectiveness of a number of non-invasive geophysical techniques, employed in conjunction with hydrogeological data, for characterising the three dimensional extent of a contaminant plume generated by septic tank effluent discharging to glacial-till subsoils at a test site within the Milltown Lake Catchment, Co. Monaghan, Republic of Ireland. It was found that the integrated use of three geophysical techniques, electromagnetics, electrical resistivity tomography and seismic refraction with existing hydrogeological and water quality data, significantly improved our understanding of the contaminant plume and associated subsurface contaminant pathways. The geophysical results, when combi...

Orr, A., Yang, L., Cachandt, G., Nitsche, J., Archbold, M., Deakin, J., Ofterdinger, U., & Flynn,... more Orr, A., Yang, L., Cachandt, G., Nitsche, J., Archbold, M., Deakin, J., Ofterdinger, U., & Flynn, R. (2017). The Influence Of Hydrogeological Setting On Nitrate Fate And Transport In Irish And British Aquifers And The Implications For Catchment Management. In International Association of Hydrogeologists Irish Group Annual Conference 2017: Proceedings (pp. 111-117). (Proceedings of the 37th Annual Groundwater Conference (International Association of Hydrogeologists, Irish Group)). International Association of Hydrogeologists (Irish Group).

Journal of Hydrology: Regional Studies, 2021

Hydrological Processes, 2021

Water Resources Research, 2019

Field data of topography, water levels, and peat hydraulic conductivity collected over a 28‐year ... more Field data of topography, water levels, and peat hydraulic conductivity collected over a 28‐year period have revealed the impacts of marginal drainage on uncut raised bog ecohydrology and its peat properties. Drainage of the regional groundwater body has induced changes in the hydraulic properties of deep peat, with peat compression decreasing hydraulic conductivity and storativity while simultaneously introducing localized secondary porosity and effective storage. Where peat has increased in hydraulic conductivity, there is a corresponding decline in vertical hydraulic gradients and significant localized increases in recharge to the underlying substrate. Repeated topographic surveys show intense localized areas of peat consolidation (>5%) where it is underlain by highly permeable (>10 m/day) glacial till deposits. More widely, continued subsidence (4–6 mm/year) of the bog surface has been measured over 900 m from the bog margin, resulting in the progressive loss of approximat...

Ecological Engineering, 2017

$Research paper thumbnail of The influence of bedrock hydrogeology on catchment-scale nitrate fate and transport in fractured aquifers$

Science of The Total Environment, 2016

Environmental Pollution, 2010

Hydrogeology Journal, 2017

Water, 2021

This study investigated the saltwater upconing mechanism in fractured coastal aquifers. Head-indu... more This study investigated the saltwater upconing mechanism in fractured coastal aquifers. Head-induced saline intrusion was initiated into three narrow sandbox aquifers containing individual horizontal discontinuities placed on different positions. Subsequently, using a peristaltic pump, freshwater was abstracted from the aquifers’ center, triggering saltwater upconing. Progressively larger pumping rates were applied until critical conditions, resulting in the wells’ salinization, were achieved. Advanced image analysis algorithms were utilized to recreate the saltwater concentration fields and quantify the extent of the saline wedges with a high accuracy. A numerical model was successfully employed to simulate the laboratory results and conduct a comprehensive sensitivity analysis, further expanding the findings of this investigation. The impact of the fractures’ length, permeability and position on the upconing mechanism was identified. It was established that the presence of high pe...

Increased water consumption combined with the effects of sea level rise and change in rainfall pa... more Increased water consumption combined with the effects of sea level rise and change in rainfall patterns have intensified seawater intrusion in coastal aquifers. Sandbox setups have been utilized over the years to recreate saline intrusion on a laboratory scale and study the mechanisms of this phenomenon. Recreating saltwater concentration fields from light intensity values is a widely applied image analysis practice in such investigations. The current paper investigates the effect of image colour depth and resolution on this procedure. Glass beads of three different diameters were utilized to recreate three homogeneous and one heterogeneous aquifer in a sandbox setup. High resolution images of saltwater intrusion were acquired using a digital camera. From these images, new ones with modified colour depth (16-bit and 8-bit) and smaller resolution were reconstructed. Deriving regression coefficients for the 16-bit experimental images was 36% ~ 51% faster than doing so for their equiva...