REFORM - WP3

Large river regulation and rehabilitation in Europe – six selected case studies

tom.buijse@deltares.nl — Fri, 04 Dec 2015 12:08:11 +0000

Large rivers have been selected as one of the satellite topics both within WP3 and WP4, because of their particular features which could not be analysed in the case study catchments framework. Large rivers are considered rivers with a catchment larger than 10,000 km² and > 100 m³/s. This encompasses rivers such as the Danube, Rhine, Rhône, Ebro, Vistula but also major tributaries such as the Sava, Narew, and Main rivers. Most fulfil major socio-economic functions, which will remain strongly modified and thus direct the options for rehabilitation. Because of their multifunctional use, large rivers can often only be partially rehabilitated or mitigated to achieve Good Ecological Potential according to the Water Framework Directive. This report addresses both hydrological modifications and restoration (rehabilitation, mitigation) following a DPSIR approach for six case studies that are spread across Europe

The historical trajectory of driving forces, river regulation (100 – 200 years) and rehabilitation (20 years) is used to underpin and illustrate the state-of–the-art regarding the effectiveness and potential of large river rehabilitation. For this, experiences and case studies from various large rivers in Europe are presented. For each case study the following information is given:

General characteristics of the river (stretch);
Description of historical state or reference condition(s) used in the rehabilitation project;
Functions of the river (stretch): for which socio-economic functions is the river used, and what are the resulting pressures for its ecological functioning?
The effects of identified pressures on hydromorphology and ecology;
Mitigation and rehabilitation measures; what measures have been taken or planned to improve the hydromorphological and ecological status of these rivers?
Ecological effects of measures.

The six case studies are representatieve of various European conditions with regard to climate, hydromorphological characteristics and catchment size. The case studies are situated in three biogeographical regions and six countries, viz. Atlantic region: River Trent (UK) and Delta Rhine (Netherlands), Continental region: Middle Vistula (Poland), Lower Danube and Po River (Italy) and Mediterranean region: Ebro (Spain). All these rivers can be characterized as large rivers (viz. catchment area larger than 10,000 km²), although they differed strongly in climatic zone, river length, catchment size, discharge, slope and river style. Large rivers can be considered as unique ecosystems and results are difficult to generalize. Still these case studies together give a good impression on the present regulation and rehabilitation of large rivers in Europe.

The case studies share but also differ substantially in drivers and associated pressures. Both flood protection and navigation are important drivers for the occurrence of many pressures. The rivers Trent, Po, Ebro and Delta Rhine have a large number of drivers and associated pressures, while the Danube Delta and middle Vistula are less impacted. For the majority no information was available regarding the extent of drivers and pressures.

There was a general pattern in the chronological sequence of the impact of drivers and associated pressures. The primal drivers for early regulation of all rivers were flood protection (embankments) and agriculture (deforestation). For most, these forms of river regulation started already centuries ago. Navigation became an important driver during the 19^th century requiring further channelisations. As a result, the occurrence of highly dynamic habitats strongly declined caused by stabilisation of the river bed (by groynes, bank protection) as well as by deepening of the main channel. Of our case studies, only the river Vistula in Poland is currently not regulated for navigation purposes, and – hence – large parts of the main channel of the river have not been channelised. More recently, especially after the Second World War, many dams were constructed in the rivers, which resulted in a decreased longitudinal connectivity, thereby impeding conditions for migratory fish and other species. Additionally, the hydrological regime of rivers was strongly altered and sediment supply to downstream sections was strongly reduced. Especially the rivers Trent, Po, Ebro and Lower Danube have been severly impacted by the construction of dams.

For the majority of the case studies, only limited information was available regarding the impacts of pressures on hydromorphology and ecology. Large rivers are impacted by multiple stressors which complicate to identify the primal causes for degradation. It seems that the sequence of drivers (and associated pressures, see above) have initiated major transition points for ecological processes and biota along large rivers. We discuss the effects briefly in respect to the time line of occurrence of these drivers and pressures.

There are some striking differences in the restoration measures taken. Along the lowland stretches of large rivers, such as the Lower Danube and the Delta Rhine, measures focus on restoring lateral connectivity gradients between main channel and floodplains. Because of constraints imposed by navigation, only a limited number of measures are taken that improve conditions for lateral migration to rejuvenate riparian zones and bar and island formation, because these will affect navigational depth in the main channel. Along the river Trent and Po (and to some extent, the Delta Rhine), measures are taken that increase variation in width and depth of the main channel, which variation is an important variable for the occurrence of several hydromorphological processes. Restoring conditions for island and shoal formation will only be carried out along the river Vistula where navigation is not an important driver.

In summary, along relatively intact river stretches, such as the Vistula and Danube delta only a limited amount of measures can already improve ecological conditions. In highly regulated rivers such as the river Trent and Delta Rhine having extensive and diverse pressures a large number of measures are required and have been taken or planned. By contrast, the Mediterranean Rivers Ebro and Po are also highly regulated, but along these rivers only a small number of measures are planned at present.

3.5_Satellite topic Large Rivers 09 Nov 2015-def.pdf

Work packages:

Deliverables:

Document type:

Report

File status:

Final

Policy Brief:

Guidance to detect impact of HyMo degradation on riparian ecosystems

tom.buijse@deltares.nl — Mon, 24 Aug 2015 10:19:29 +0000

The aim of this deliverable is to address the impact of hydromorphological degradation on floodplain and riparian ecosystems, with specific focus on vegetation, fish and invertebrate responses and to provide guidance on how to identify those impacts.

An introductory chapter summarises the research context and reviews the lessons for managers and stakeholders. Based on the results of the analyses, and the river styles typology developed in Work Package 2 of REFORM, a generic process is recommended for assessing the impact on floodplain and riparian ecosystems, incorporating our key findings. It also highlights the usefulness and limitations of existing EU Directives in providing a suitable legislative framework.

Assessments of instream impacts on riverine ecosystems make use of multi-site datasets, riparian and floodplain ecosystems are not subject to this type of extensive monitoring; hence, the results presented here are based primarily on case studies from across Europe.

A key finding is that impacts to hydromorphological processes and that these impacts can take years to fully manifest themselves. The results can be dramatic with changes in river style and loss of riparian forest as unpredicted outcomes of human intervention.

We spotlight vegetation, unlike other biota, it has a very direct influence on fluvial geomorphological and hydrological processes, by stabilising sediments and influencing flood conveyance. A number of case study contributions address various forms of this key interaction. A short summary chapter is provided to link these findings to this particular theme. Use of the vegetation-process model developed in WP2 is recommended to compare the post impact role of the physical processes of vegetation with the ‘natural’ conditions. This model is used in all the vegetation case studies and helps explain why impacts can take time to become fully manifested.

In three Italian case studies, on the Magra, Panaro and Aurino rivers, the channels narrowed and the beds encised following a variety of impacts including gravel mining and catchment scale deforestation. This altered the patterns of riparian vegetation and tree growth. The three case studies also highlight the complexity of the relationships occuring between riparian vegetation and river hydromorphology in impacted rivers and how human disturbances may become dominant in structuring such relationships. The case study examples confirm that plant diversity alone cannot be considered a valid and exhaustive indicator to assess the health of a river system and its functioning.

For the two Spanish case studies aerial photographic data was available before and after damming of the rivers. After damming, vegetation encroachment on downstream gravel bars stabilised the banks and the channel changed from braided to single threaded. Similar effects of flow regulation have been reported on other rivers. In the River Porma, the vegetation composition and structure changed from one dominated by young pioneer species to a mature forest with a dense overstory of late-seral species near the channel banks. In the case of the River Guadalete, the flow regulation reduced the recruitment potential of native species and favoured the exotic species Eucalyptus camaldulensis. As a direct consequence of flow regulation, areas affected by fluvial disturbances under pre-dam conditions have turned into areas dominated by hydrologic processes with negligible sediment dynamics during inundation. Based on these results key indicators of change are proposed.

In Austria, the River Traun is regulated via a flood protection dam that cuts off the river from its floodplain and side arms and wet areas of the riparian forest have dried up. The river is deeply encised, and this has caused a significant lowering of the groundwater table with a consequent loss of riparian forests. The River Traun study site is representative of a large number of European rivers where the typical shruby pioneer vgetation and softwood riparian forests have disappeared and been replaced by mainly hardwood riparian forests that constitute the largest part of the remaining European riparian forests.

In Poland, the low energy river Narew is one of the few remaining anastomising river systems in northern Europe. This river type was once common and widespread but is now confined and regulated across much of its historic distribution. The Narew has been subject to flow regulation in parts of its catchment. The analysis of inundation duration for the period 1978-2009 shows that the vulnerability to changes in the flood regime, induced by damming upstream, is habitat dependent and related to the duration of flooding. In the case of wetlands sedge Phalaris and Carex-Phalaris communities, their natural inundation periods are relatively short. These communities were affected by the change in the flood frequency, while other communities were unaffected. The study demonstrated that natural (or semi-natural) lowland river valleys can be quite resistant to a single pressure, in this case flood frequency changes.

We also provide primary research on invertebrates and fish responses to riparian degradation. In Scotland, three rivers subject to varying degrees of flow regulation were studied, two of which are Special Areas of Conservation. The response of riparian invertebrates to flood inundation on mid-channel islands was studied. Overall, the insensitivity of these riparian invertebrate assemblages to flow peak or intensity floods suggests that the community structure is resilient. High abundance of Carabidae indicates a system unaffected by floods, suggesting that the system is hydrologically impaired. More important environmental factors were the size and habitat structure of the riparian habitat. The semi-natural habitat in the surrounding landscape provided a source of colonists.

Swedish streams in catchments with natural (forest) and degraded (agriculture) riparian zones were compared. Degradation of the riparian zones had important effects on in-stream hydromorphology (riffle and pool sections) and instream invertebrate communities (changes in species traits composition). The agricultural streams characterised by long stretches of pool habitat are less likely to support insects with traits favouring greater dispersal than forested streams with a higher abundance of riffles. This in turn affects the subsidy of energy and nutrients to the riparian zone, in the form of aquatic insects emerging as adults and dispersing into the riparian zone. This implies that the few short riffle habitats in the agricultural landscape are important for the transfer of high quality food to terrestrial/riparian consumers.

In the Danube Delta, Romania, fish communities have been significantly affected, locally, by loss of connectivity between the main stems of the river and floodplain lakes. The lakes have high species diversity due to the co-occurrence of rheophilic, eurytopic and limnophilic forms. Analysis of long-term data on commercial fishing and the history of hydrotechnical works indicates negative changes in the catch, which correlates well with the blocking of canals to alleviate siltation and nutrient inputs. Alternative solutions should now be considered. Reliable long-term commercial fishery data on migratory anadromous and potamodromous fish species can be used to indicate and explain effects of historical changes in the lateral or longitudinal connectivity of river systems. From a management point of view, maintaining the existing connectivity gradient in the delta lakes is vital for biodiversity conservation and economic needs.

3.4 Guidance to detect impact of HyMo degradation on riparian ecosystems.pdf

Work packages:

Deliverables:

D3.4 Guidance on how to identify impacts of hydromorphological degradation on riparian ecosystems

Document type:

Report

File status:

Final

Policy Brief:

Evaluation of candidate biological indicators of hydrological and morphological degradation

tom.buijse@deltares.nl — Sun, 28 Jun 2015 09:34:03 +0000

Work Package 3 of REFORM focuses on the impacts of hydromorphological changes on river and floodplain ecosystems. The main research objectives of deliverable 3.3 are:

To establish empirical relationships between the biota, flow dynamics, substrate complexity/habitat heterogeneity and sediment dynamics.
To select and develop candidate indicators for WFD quality elements that quantify impacts of hydrological and morphological degradation in rivers.
To develop novel biological indicators capable of diagnosing hydromorphological stressors in a multiple stressor environment.
To advise on the design of monitoring programs to detect hydrological and morphological degradation.
To address the importance to quantify uncertainty in biology based hydromorphological assessment and discuss the implications of uncertainty for monitoring and assessment.

The empirical relationships between biota, flow dynamics, substrate complexity and sediment dynamics are investigated in chapter 1. The performance of existing indicators/metrics to assess hydromorphological degradation has been determined in a case study of the Regge catchment in the Netherlands and a study of Danish streams (Chapter 2). Novel designs for developing ‘new’ diagnostic metrics to solve issues related to multiple stressors including hydromorphological stress are presented in Chapter 3. Subsequently chapter 4 describes how monitoring programs can be designed to assess hydromorphological degradation using biological indicators. Finally, chapter 5 adresses the importance to quantify uncertainty with its implications for monitoring when assessing the ecological status of river systems.

Conclusions and recommendations:

Empirical relationships

Invertebrates– The experiment described in chapter 1.1 showed that the effects of patchiness and flow on lowland stream caddisflies are species-specific. The wide range of effects found in the experiment indicates that small-scale heterogeneity in the form of substrate patchiness is an important driver of the community patterns in streams and that change in substrate composition or spatial arrangement of patches due to natural or anthropogenic disturbances could have considerable effects on macroinvertebrate populations.

The experimental addition of fine sediment (chapter 1.2) to the substrate affected oxygen penetration, nutrient concentrations (ammonium, nitrate, nitrite and SRP), and both benthic and hyporheic invertebrate assemblage structure. Different flow rates also affected these attributes. Nevertheless, the hypothesis that higher flows would ameliorate any effects of added fines, although generally supported for oxygen penetration, was not supported for benthic or hyporheic invertebrates (no interaction between flow type and sediment treatment). However, the rates of flow used in the mesocosms did not appear to reach the threshold required to remove fines or alter sediment dynamics.

Periphyton– Experimental results (chapter 1.3) support the assumption that fine sediment has the potential to confound investigations of other stressors on periphyton in river environments, including phosphorous concentration (Jones et al. 2014). Under reduced phosphorous conditions the chlorophyll-a and ash-free dry weight concentrations were lower with sediment treatment. Whereas, under control conditions, the sediment treatment showed increased chlorophyll-aand ash-free dry weight concentrations. This is an interesting result, and clearly needs further study, as it has potential implications for management and other studies involving phosphorous reduction in river systems.

Performance of existing indicators

Macroinvertebrates– River zonation preferences (upstream vs downstream species) have the potential to indicate hydrological and/or morphological stress (chapter 2.1). Although overlap between samples of different quality classes is apparent, locations of good hydrological or morphological quality are dominated by upstream or rhithral species, whereas downstream or potamal species are more abundant in locations of poor hydrological or morphological quality.

Macrophytes- The Danish Stream Plant Index (DVPI) declined with increased frequency of weed cutting (chapter 2.2). A significant relationship was found also between DVPI and stream morphology (channel sinuosity and profile) in small streams. Such a relationship was not detected in middle-sized and large streams most likely reflecting that weed cutting often correlates with the degree of channelization, thereby making it difficult to distinguish these two types of impacts in these stream types.

Novel metrics

Macroinvertebrates- AMOEBE provides an appealing visual tool for water managers to diagnose the cause of stream degradation, including morphological and hydrological degradation (chapter 3.1). Because AMOEBE is a diagnostic tool it makes it easier to decide on appropriate restoration measures when a stream fails to meet the ecological quality objectives. Apart from AMOEBE, macroinvertebrate traits, that are indicative of low and high fine sediment conditions, have been identified (chapter 3.4). This indicates the potential to develop a biological trait-based index for fine sediment stress. It further validates the incorporation of the metric percentage of silt dwelling species in the AMOEBE, and also offers potential for improvement of AMOEBE in the future.

Fish- For fish the overall shape of size spectra was identified as a potential novel metric for assessing impacts of hydromorphological pressures and restoration projects.

Diatoms- Results suggest, in line with deliverable 3.1, that the TDI scoring system, developed to assess the degree of eutrophication, is robust to hydromorphological stress (percentage cover of fine sediment). Furthermore, no relationship between motility (proposed metric of sediment stress based on phytobenthos) and sediment stress could be detected. However, the strong influence of fine sediment on diatom community composition indicates the potential for a robust metric relating diatoms to fine sediment.

Designs for monitoring

The results from chapter 1, 2 and 3 suggest it is possible to develop indices for fish, macroinvertebrates and diatoms that can indicate (hydrolo)morphological degradation. Results described in deliverable 2.2 clearly demonstrate the importance of both aquatic and riparian vegetation as a key physical control of river form and dynamics and a crucial component of river restoration. This, in combination with the diagnostic tool AMOEBE descibed in chapter 2, is a first step in the development of stressor specific bioassessment methods.

Uncertainty

Based on current literature it is very difficult to gain insight on the extent to which different sources of variation (i.e., natural spatial, natural temporal, and within-site variation) contribute to overall variation (Vlek, 2014). Also, information on variability varies depending on the metric, ecological status and stream type studied and the monitoring techniques applied. It is, therefore, unlikely that data on variation/uncertainty can be applied universally. So, instead of providing quantified information on variation/uncertainty, chapter 5 provides guidelines to develop a biological assessment system that is both affordable and provides managers with meaningful results.

3.3 Evaluation of candidate hydromorphology indicators.pdf

Work packages:

Deliverables:

D3.3 Evaluation of candidate indicators for case studies including uncertainty

Document type:

Report

File status:

Final

Policy Brief:

Understanding biological responses to degraded hydromorphology and multiple stresses

tom.buijse@deltares.nl — Fri, 06 Mar 2015 12:33:53 +0000

The aim of this deliverable is to conceptually model and empirically test the response of biota to the effects of both hydromorphological pressures acting in concert with one another or with other types of pressures. Best use is made of existing large national monitoring datasets (Denmark, UK, Finland, France, Germany, Austria & WISER datasets), case studies and modeling to provide evidence of multiple stressors interacting to alter river biota (Biological Quality Elements: BQE).

In-stream river plants. The evidence from analyzing plant traits, from UK, German and Danish data is that macrophytes can indicate hydromorphological degradation. One can also gain insights into how different hydromorphology and other stressors are interacting. Channelised sites are not only physically altered but require ongoing maintenance in the form of vegetation management (riparian and in-stream) and dredging which impact on macrophyte traits. The observed interactions between eutrophication and different hydromorphological pressures are explored. There was also evidence that macrophytes may have a role in accumulating/retaining heavy metals in polluted rivers; a fact which requires consideration during the physical restoration of such systems.

Fish. The sensitivity of species with different physical habitat affinities is considered. The response of fish to over 100 years of hydromorphological degradation at three Austrian case study systems is described. Here the complex nature of hydromorphological impacts on hydromorphological processes is emphasised. In a second study the possibility of creating models which link pressure to processes to fish occurrence is explored. As a pressure may affect more than one hydromorphological process it is important to understand and clear define how pressures interact on physical processes at scales that fish respond to.

Invertebrates. Existing invertebrate metrics are problematic. To explore alternatives we aimed to elucidate general patterns between the assessment of habitats/biotopes and the diversity of macroinvertebrates using a standardised biomonitoring sampling methodology. We use a high quality dataset that includes a pre-defined gradient in hydromorphological degradation. In addition to identity-based diversity metrics and traits were used. There was some evidence that traits held some potential but sampling methods also need to be revised.

Joint (BQE) Biota Analysis.Analysis of a very large European data set covering Finland, Denmark and France examined the relative sensitivity of macrophytes, diatoms and invertebrates to nutrient and hydromorphological stresses. Analysis at the community level suggested that nutrient impacts were more detectable than hydromorphological stressors. This finding is not surprising for Finland where hydromorphological degradation is rather low. Sites subject to multiple-stresses tended to have the most common species. There are differences in sensitivity between BQEs at community level; primary producers appear more sensitive to diffuse pollution than invertebrates. The challenges in using monitoring data to identify known causal interactions between biota and multiple stressors are discussed.

Weir removal. This intervention is now widely advocated across Europe as a means of improving ecological status. The benefits of weir removal are obvious, for example its removal facilitates upstream migration of anadromous fish; but in multi-stressor environments there may also be unforeseen disadvantages. The removal of a weir from a British weir is modeled and checked against empirical data. The results indicate that the weir creates conditions for denitrification and its removal increases the load of N exported downstream. The cumulative impact of widespread weir removal should be considered carefully in terms of the gross export of rivers to coastal areas where catchments suffer from eutrophication.

Stressor interactions.A clear conclusion from the evidence available across all biotic groups is that irrespective of whether or not hydromorphological stressors and other forms of stress interact synergistically or antagonistically to alter natural river biota assemblages, each stressor on its own can and do have detrimental impacts. Therefore when remediating damaged sites it is important to understand that while it may be possible to improve system status by tackling one stressor good ecological status is unlikely to be achieved without tackling all significant stressors in systems subject to multiple stress.

Future Directions. Monitoring data are designed to detect change at individual sites through time and can miss some crucial hydromorphological impacts. Revision of some of the monitoring metholodologies can help, however adherence to monitoring data alone will not supply knowledge and system understanding. Common sense indicates an alternative approach for some WFD operational and investigative monitoring are well designed, replicated field ‘experiments’ elucidate cause-effect relationships on case study systems and are used to complement monitoring data, see WP4 for examples.

3.2 Biological_responses_to_degraded_HyMo_and_multiple_stress.pdf

Work packages:

Deliverables:

D3.2 Understanding biological responses to degraded hydromorphology sediment dynamics and multiple stress

Document type:

Report

File status:

Final

Policy Brief:

Impacts of hydromorphological degradation and disturbed sediment dynamics on ecological status

tom.buijse@deltares.nl — Thu, 28 Nov 2013 13:40:12 +0000

The purpose of WP3 is to address degraded river systems. The aim of the first deliverable D3.1 was to begin the development of metrics which indicate the impact of hydromorphological degradation on biota using existing data. The output, an informed choice of key metrics, aims to support the stakeholder decision making processes and their ability to target desired project goals. These indicators of degradation should be viewed as an interim solution while a more comprehensive and tested approach is produced from WP2 and the final system developed will be an integral part of WP6.

Background

The purpose of WP3 is to address degraded river systems and under D3.1 to specifically look at impacts of hydromorphological degradation on ecological status using existing data. The aim of the work was to begin the development of metrics which indicate the impact of hydromorphological degradation on biota. The authors were conscious of the need of stakeholders to both evaluate current condition but also evaluate the success of river rehabilitation projects.

HYMO indicators of degradation

A possible approach for developing a method of evaluating the ecological and morphological conditions of a river influenced by human intervention is presented. The method is based on a source pool of detailed physical parameters and indicators (metrics) that are linked to the data and outputs of other work packages (WP1 & WP2) within the REFORM Project. Depending on the focus of an evaluation (to choose from morphology, vegetation, benthos and/or fish), experts can use these approaches to identify a subset of key indicators from this pool. When using the approach an evaluation is performed comparatively between the benchmark condition of the river and the river condition affected by human intervention. The output, an informed choice of key metrics, aims to support the stakeholder decision making processes and their ability to target desired project goals. These indicators of degradation should be viewed as an interim solution while a more comprehensive and tested approach is produced from WP2 and the final system developed will be an integral part of WP6. The impact of hydromorphological degradation on individual biological Quality elements is reviewed in the subsequent chapters.

Brief overall conclusions

· There is an acknowledged need among stakeholders that new hydromorphological metrics are required to facilitate site remediation and for reporting at national and European levels.

· Pressure/ impact data were assembled from across Europe. The task was challenging, but useful information was gathered.

· For each major hydromorphological pressure, the physical response gradients of rivers was summarised as diagnostic diagrams.

· For the first time we provide evidence that metrics indicating HYMO impact could be developed from monitoring data on fish and macrophytes.

· For the first time we demonstrate the potential to derive metrics sensitive to fine sediment.

· We provide evidence that phytobenthos (diatoms), invertebrates and macrophytes have the potential to be used in combined metrics.

· We found that many existing macroinvertebrate metrics lack specificity and can provide false positive responses to HYMO pressure, suggesting that disentanglement of multi-stressor responses is critical to good diagnosis.

· There is evidence that aquatic habitats protected under the Habitats Directive will be increasingly vulnerable to hydrological pressures with the changing climate.

· Frequently, overlooked topics such as sediment quality and groundwater issues ought to supplement or be included in HYMO assessments due to their potential for explaining variance in biological datasets.

· Land-use data on a spatial scale beyond the reach scale (corridor and catchment) relates to site-specific macroinvertebrate metrics and could be a more robust way of assessing impacts.

3.1 Impacts of HyMo degradation on ecology.pdf

Work packages:

Deliverables:

D3.1 Impacts of hydromorphological degradation and disturbed sediment dynamics on ecological status