Damian Lawler

Use of continuous turbidity sensor in the prediction of fine sediment transport in the turbidity maximum of the Trent Estuary, UK

Results from continuous monitoring of turbidity and water level at Burringham, on the tidal River Trent, UK, are presented for the period 18 May 1997 to 9 February 1998. These measurements, together with detailed readings of velocity and suspended sediment concentration over an individual tidal cycle near the opposite bank at Derrythorpe, help to describe the mechanisms and behaviour of the turbidity maximum (TM). It is demonstrated that there is a distinct pattern of fine sediment movement that reflects a predictable system response to changing hydraulic features. It is shown that the TM in this system is highly mobile, and its location depends on antecedent fresh water flow, and tidal range. Approximate representative flood and ebb tide suspended sediment concentrations of up to 13 g/l over this nine-month period have been derived from the data and plotted against fresh water flow and tidal range, in order to show the relationship between these parameters. Three semi-empirical polynomial regression models have been tested for goodness of fit against available data. It was found that a partitioning approach, whereby data are grouped into different categories depending on antecedent fresh water flow, yielded the lowest standard error for the period analysed. Analysis of detailed observations of suspended sediment concentration and velocity measured over an individual tidal cycle also help to elucidate the mechanism of tidal pumping within this system. These results also help to give an estimate of the relative magnitude of suspended sediment fluxes during typical low fresh water flow conditions. It is estimated that for low fresh water flow conditions, a typical spring tide can mobilise at least an order of magnitude more sediment than a neap tide.

Large-Scale Climatic Controls on New England River Flow

Abstract Understanding atmospheric drivers of river flow variability necessitates clear knowledge of the process chain linking climate and hydrology, yet the nature of such linkages remains poorly understood for the New England region of the northeastern United States. This research gap is addressed through a composite analysis of large-scale climatic controls on monthly high and low river flow in New England for 1958–2001, based on 40-yr ECMWF Re-Analysis (ERA-40) data. Analysis is focused on climate fields at the North Atlantic spatial scale, with particular attention given to the influence of the North Atlantic Oscillation (NAO). High (low) river flow is shown to be characterized by greater (lower) geopotential height throughout the year, and from December to April, higher (lower) temperature. Wind speed is inversely associated with river flow in all months, with wind direction more southerly (northerly) under high (low) flow situations. Relative vorticity differences reveal more cyclonic circulation c...

Measuring sediment exchange rates on an intertidal bank at Blacktoft, Humber Estuary, UK

Results from a suite of Photo Electronic Erosion Pins (PEEPs) and manual pins installed on an intertidal bank at Blacktoft, near the confluence of the Rivers Trent and (Yorkshire) Ouse, UK are presented for summer 1997 (1 May-28 September). These reveal a pattern of erosion and deposition, which can be related to variations in tidal range, freshwater flow and wind speed over the period. During spring tides, greater resuspension of bed sediment leads to a greater availability of sediment in the water column for deposition on the bank. High wind speeds cause greater erosion of material from the bank due to wind-induced wave action. These processes of sediment exchange are also modified by the effects of biological activity on the sediment and of consolidation. It was demonstrated that the mean daily change in elevation of the upper part of the bank at Blacktoft was approximately 11 mm, which is two-three-fold less than the equivalent figure measured by a similar method at Burringham on the River Trent. It is thought that this difference is due to the effects of a greater concentration of suspended sediment settling onto the banks at Burringham, which are also subject to greater erosion due to their steeper slope. Results from a longer and more widespread survey of eight other intertidal banks in the Trent-Ouse Estuary system suggest that deposition and erosion occur in phase on all intertidal banks within the study area. Intertidal banks towards the upstream end of the system show much less variation in bank level than those further downstream.

Dynamics of erosion and deposition events on an intertidal mudbank at Burringham, River Trent, UK

Measurements using an automatic bank level monitoring technique [the photoelectronic erosion pin (PEEP) system] over a 70-day period between 16 March and 27 May 1997 have revealed a complex pattern of erosion and deposition on an intertidal mudbank on the River Trent at Burringham. Comparison of mean daily changes in bank elevation at upper and lower bank positions suggest that wave activity induced by high wind speeds causes erosion, while high tidal range leads to deposition as a result of higher suspended solids concentrations. A greater variability in mean daily erosion and deposition events at the lower bank compared with the upper bank appears to indicate that higher bed shear stresses, as well as a greater availability of sediment for settling, owing to higher concentrations and a greater depth of water, lead to a more dynamic exchange of material at this position. The PEEP data also show longer term trends in sedimentation, with the mean deposition for the period exceeding mean erosion. Manual erosion pin measurements at a lower frequency over a longer, seven-month period confirm this, and also highlight the advantage of the PEEP system in monitoring events at a finer temporal resolution. Copyright

Sediment and Solute Yield from the Jökulsá á Sólheimasandi Glacierized River Basin, Southern Iceland

This chapter discusses change and variability in suspended sediment and solute concentration, load and yield for the Jokulsa a Solheimasandi glacial river system in southern Iceland. Using a combination of low-frequency Icelandic Hydrological Survey data for the 1973–1988 period and the author’s results from intensive monitoring of water quality in the 1988 melt season, variations are examined at three timescales: inter-annual, seasonal and diurnal. The combined yield of suspended sediment and dissolved material is 14,5001 km-2a-1, equivalent to an erosion rate of 5.4 mm a-1, which is one of the highest values recorded anywhere. Slight restrictions on suspended sediment concentration, however, possibly associated with longer-term exhaustion effects, may now exist. One reason for caution in the interpretation of these estimates, however, is the pronounced variability, at all timescales, of runoff and sediment output from this basin, particularly in relation to the low-frequency data available. High seasonality of flow and sediment output typical of glaciofluvial systems occurs here, and a clear peak in total flux from the system emerges in the July-September period, when discharge, suspended sediment loads and solute loads all reach their maxima.

The impact of cattle access on ecological water quality in streams: Examples from agricultural catchments within Ireland

Unrestricted cattle access to rivers and streams represent a potentially significant localised pressure on freshwater systems. However there is no consensus in the literature on the occurrence and extent of impact and limited research has examined the effects on aquatic biota in the humid temperate environment examined in the present study. Furthermore, this is one of the first times that research consider the potential for cattle access impacts in streams of varying water quality in Northern Europe. We investigated the effects of cattle access on macroinvertebrate communities and deposited fine sediment levels, in four rivers of high/good and four rivers of moderate water quality status which drain, low gradient, calcareous grassland catchments in Ireland. We assessed the temporal variability in macroinvertebrates communities across two seasons, spring and autumn. Site specific impacts were evident which appeared to be influenced by water quality status and season. All four high/good water status rivers revealed significant downstream changes in community structure and at least two univariate metrics (total richness and EPT richness together with taxon, E and EPT abundance). Two of the four moderate water status rivers showed significant changes in community structure, abundance and richness metrics and functional feeding groups driven in the main by downstream increases in collectors/gatherers, shredders and burrowing taxa. These two moderate water status rivers had high or prolonged livestock activity. In view of these findings, the potential for some of these sites to achieve at least high/good water quality status, as set out in the EU Water Framework Directive, may be compromised. The results presented highlight the need for additional research to further define the site specific factors and livestock management practices, under different discharge conditions, that increase the risk of impact on aquatic ecology due to these cattle-river interactions.

A systematic quality assessment of Environmental Impact Statements in the oil and gas industry

The global economy relies heavily on oil and gas resources. However, hydrocarbon exploitation projects can cause significant impacts on the environment. But despite the production of numerous Environmental Impact Statements (EISs) to identify/mitigate such impacts, no study has specifically assessed the quality of EISs for both onshore and offshore oil and gas projects, with tested hypotheses. To address this research gap, our paper, for the first time, develops a modified Lee and Colley evaluation model to assess the quality of 19 sampled oil and gas project EISs produced from 1998 to 2008 in Nigeria. Our findings show that Project Description and Communication of Results are the main areas of strength. However, Environmental Impact Prediction, and Project Decommissioning, were among the key areas requiring attention. A key finding, though, is that Mann-Whitney tests suggest that there is no evidence that the quality of EISs for the latter period (2004-2008) is higher than that of the earlier period (1998-2004). We suggest that periodic systematic review of the quality of submitted/approved EISs (c. every 3-5years) should be established to monitor trends in EIS quality and identify strong and weak areas. This would help to drive continual improvement in both the EIA processes and the resultant EISs of technical engineering projects. Such reviews have the potential to illuminate some of the underlying problems of, and solutions to, oil and gas exploration, production and transportation, and their related environmental impacts. This suggested change would also be useful internationally, including for the burgeoning exploration and production of unconventional hydrocarbon resources.

Evaluating the relationship between biotic and sediment metrics using mesocosms and field studies.

An ongoing research challenge is the detection of biological responses to elevated sediment and the identification of sediment-specific bioassessment metrics to evaluate these biological responses. Laboratory mesocosms and field observations in rivers in Ireland were used to evaluate the relationship between a range of biological and sediment metrics and to assess which biological metrics were best at discerning the effects of excess sediment on macroinvertebrates. Results from the mesocosm study indicated a marked decrease in the abundance of sensitive taxa with increasing sediment surface cover. % EPT (Ephemeroptera, Plecoptera, Trichoptera) and % E abundances exhibited the strongest negative correlation with sediment surface cover in the mesocosm study. The field study revealed that % EPT abundance was most closely correlated with % sediment surface cover, explaining 13% of the variance in the biological metric. Both studies revealed weaker relationships with a number of other taxonomy-based metrics including total taxon abundance, total taxon richness and moderate relationships with the Proportion of Sediment-sensitive Invertebrates metric (PSI). All trait-based metrics were poorly correlated with sediment surface cover in the field study. In terms of sediment metrics, % surface cover was more closely related to biological metrics than either re-suspendable sediment or turbidity. These results indicate that % sediment surface cover and % EPT abundance may be useful metrics for assessing the effect of excessive sediment on macroinvertebrates. However, EPT metrics may not be specific to sediment impact and therefore when applied to rivers with multiple pressures should be combined with observations on sediment cover.

Interannual to interdecadal variability of winter and summer southern African rainfall, and their teleconnections

This study examines for the first time the changing characteristics of summer and winter southern African rainfall and their teleconnections with large-scale climate through the dominant time scales of variability. As determined by wavelet analysis, the austral summer and winter rainfall indices exhibit three significant time scales of variability over the twentieth century: interdecadal (15–28 years), quasi-decadal (8–13 years), and interannual (2–8 years). Teleconnections with global sea surface temperature and atmospheric circulation anomalies are established here but are different for each time scale. Tropical/subtropical teleconnections emerge as the main driver of austral summer rainfall variability. Thus, shifts in the Walker circulation are linked to the El Nino–Southern Oscillation (ENSO) and, at decadal time scales, to decadal ENSO-like patterns related to the Pacific Decadal Oscillation and the Interdecadal Pacific Oscillation. These global changes in the upper zonal circulation interact with asymmetric ocean-atmospheric conditions between the South Atlantic and South Indian Oceans; together, these lead to a shift in the South Indian Convergence Zone and a modulation of the development of convective rain-bearing systems over southern Africa in summer. Such regional changes, embedded in quasi-annular geopotential patterns, consist of easterly moisture fluxes from the South Indian High, which dominate southerly moisture fluxes from the South Atlantic High. Austral winter rainfall variability is more influenced by midlatitude atmospheric variability, in particular the Southern Annular Mode. The rainfall changes in the southwestern regions of southern Africa are determined by asymmetrical changes in the midlatitude westerlies between the Atlantic and Indian Oceans.

Towards the Implementation of SEA — Learning from EIA for Water Resources

The main purpose of SEA is to facilitate early and systematic consideration of potential environmental impacts in strategic decision-making’ (Finneveden et al. 2003 p.92). In short, it is to take a longer-term and more holistic view of environmental effects and sustainability than is possible for the project-based foci of EIA. It was made official in the EU in July 2001 under the SEA Directive, with a margin of discretion allowed for member states to propose their own procedures, integration timescales and legislative frameworks, although 21 July 2004 was the published application date (Risse et al. 2003). SEA deals with plans, policies and programmes, although the SEA Directive focuses on plans and programmes. Of additional relevance to water resources is the Water Framework Directive (see also Chap. 35) which place responsibilities on governments, environmental protection agencies and regulators to ensure an appropriate quality and quantity of water for a nation’s human population and its ecosystems. This has led to many recent papers from the EU dealing with sustainable watershed management (e.g. Hedo and Bina 1999; Tsakiris 2002). This normally includes some kind of Environmental Assessment (EA) process. This chapter proposes that we can use lessons learned from project EIA to improve the implementation of SEA. The principle of what is termed here ‘EIA-SEA experience linkage’ is evident in EA studies. For example, Noble (2004) implicitly took this approach in the case of the role of assessment panels in SEA, and Finnveden (2003) comments explicitly on the useful transfer of EIA principles to SEA policy development, although the applicability of EIA methods may be less straightforward. The chapter is timely, given the lack of current methodological guidance for SEA components, and it is hoped that it can contribute to the development of SEA principles, approaches, methods and tools that will undoubtedly take shape over the next ten years.