River Restoration Research Articles

Performance of an environmentally‐aligned, low maintenance flood alleviation scheme on the Burn of Mosset, Forres, Scotland

AbstractFlooding of the town of Forres, Scotland prompted the implementation of a flood alleviation scheme (FAS) featuring a low earth‐fill dam constructed upstream of the town to create a flood retention area, limiting peak discharges entering the urban area. Flow through the dam is controlled by a weir, and it was recognised that if coarse sediment, large wood, and/or debris collected at the weir this could adversely affect its performance. To ensure reliable operation of the weir, the “Burn Management Works” (BMW) were designed to reconnect the embanked, elevated river channel to its floodplain, naturally retaining coarse sediment, large wood, and debris upstream of the dam. The FAS became operational on August 28, 2009 and impounded floodwater for the first time just 1 week later. Here, we report the results of monitoring of the BMW performed between 2011 and 2018. We find that the BMW have fulfilled their primary, flood alleviation functions by retaining large amounts of sediment and large wood without the need for maintenance. In so doing, the BMW has evolved from the single‐thread, trapezoidal, pilot channel constructed through the initially dry pasture, to the shifting mosaic of anastomosed channels, ponds, wetlands, and scrublands that now comprise the fully‐connected floodplain. In parallel, local interest groups have transformed this flood defence asset into a bird and wildlife area that is enjoyed by the community. Lessons learned from the BMW can inform other projects seeking to use nature‐based solutions to deliver sustainable flood risk management while simultaneously achieving goals for river restoration and community engagement.

Environmental information disclosure and public choice decisions for urban river restoration: A comparative study between Brussels (Belgium) and Guangzhou (China)

Worldwide environmental information disclosure (EID) has been widely promoted as a policy approach to establish transparent governments, enhance public environmental awareness, and foster participatory environmental governance. While information disclosure and transparency are inherently incentivised within democratic regimes, how and through what pathways an increased flow of environmental information in the absence of democracy could lead to favourable public support for environmental/ecological projects remain under-investigated. Particularly, there exists very limited literature which compares how EID is associated with public environmental choices between different sociopolitical contexts. Taking Brussels (Belgium) and Guangzhou (China) as a comparative case, this study examines the association between citizens' perceived trustworthiness of various environmental information sources and their choice decisions regarding urban river restoration initiatives in contrasting socialpolitical contexts. Latent class modelling of two paralleled discrete choice experiments unveils a consistent classification of three distinctive groups for each city and also the combined sample, including Enthusiastic Supporters (Class 1, who are cost-insensitive and supportive of all proposed changes), Pragmatic Supporters (Class 2, who are cost-sensitive, prefer some changes they favour), and Non-Supporters (Class 3, who are unwilling to support the proposed initiatives). Incorporating respondents' trustworthiness in information sources as covariates in class membership likelihood function, respondents' membership is found to be associated solely with the most trusted information source, i.e., social contacts in Guangzhou, third parties in Brussels, and social contacts for the whole sample. Holding trust toward the most-trusted information source can increase the probability of being a member of Class 1, otherwise, more likely being a member of Class 3. Taken together with the insignificance of the variable denoting a respondent's city in explaining class membership, this study reveals that the variations in the EID levels (matured vs. emerging) and sociopolitical contexts (democratic vs. non-democratic) cannot significantly shape citizens' environmental decisions. Instead, it is respondents' perceived trustworthiness of information outlets that plays a positive role in their supportive decisions. These analytical results offer new insights about the role of EID in environmental governance and call for instilling institutional trust in China and relational trust in Belgium for facilitating effective communication and pro-environmental behaviours across the whole community.

River habitat assessment and restoration in high dam flood discharge systems with total dissolved gas supersaturation

The success of river habitat restoration relies on accurate assessment proxies. However, determining how to quantitatively assess the impact of multiple stressors during flood discharge from high dams in riverine ecosystems and where and how to implement more reliable recovery interventions remain challenges. Here, we developed a bottom-up mechanistic framework for assessing the effects of total dissolved gas supersaturation (TDGS) and hydrodynamics on fish habitat quality and applied it to the downstream river reach of the Xiangjiaba Dam in Southwest China. The results showed that the available habitat area of river sturgeon was the smallest, while Chinese sucker had the largest available habitat area among the three target species under all discharge scenarios. Although the TDGS levels were evenly mixed laterally, the habitat suitability index indicated that the suitable habitats were primarily within both sides of the river reach under all scenarios, which is contrary to findings based on the traditional TDGS risk assessment model. The traditional TDGS risk assessment model overestimates the impact of dams on habitats. This divergence reflected the sensitivity of the habitat assessment to fish habitat preferences, fish tolerance to TDGS and the biological response of fish under TDGS. Additionally, the priority areas for restoration can be identified by habitat suitability index with lower values. We simulated twenty-four schemes and found that interventions such as stone groups, ecological spur dike, water-retaining weir and river dredging can enhance habitat suitability for fish species under multiple stressors, providing novel insights into where and how to mitigate the impact of TDGS. Our findings offer a transferable framework for the quantitative evaluation of fish habitat and implementation of restoration management during dam flood discharge periods, thus providing a new perspective for biodiversity conservation and habitat restoration in dam-regulated rivers with TDGS around the world.

On the Prediction of the Characteristic Times of River Meander Cutoff Sequence: Theoretical Model and Comparison With Laboratory and Field Observations

AbstractRiver meander dynamics inevitably interferes with a number of human activities and productive processes. Therefore, investigating the involved physical processes and modeling their space‐time evolution represent a crucial requirement in terms of sustainable river management and restoration planning. In the present study, a deterministic integral‐differential equation that governs river‐bend growth and death in the absence of natural or anthropic forcing is for the first time derived and solved by resorting to cardinal fluid‐mechanical equations such as Navier‐Stokes’ in the Lamb‐Oseen version. The related 1‐D model, which accounts for morphology and sedimentology via the meander migration rate and its radius of curvature, proves to be able to grasp the periodic nature of the phenomenon. Additionally, it exhibits an overall very good agreement with field pre‐cutoff and post‐cutoff observations, as well as with the outcome of an ad hoc‐designed laboratory experiment that simulated near‐cutoff conditions. Hence, it may represent a fast and easy tool to monitor river bend hydro‐geomorphological evolution, particularly when the signs of the incipient instability suggest quantifying the time left to its routine exploitation and to timely plan, where needed, suitable management and restoration interventions.

Rivers under pressure: Interdisciplinary feasibility analysis of sustainable hydropower

AbstractGlobal biodiversity loss is most severe in freshwaters, particularly in river ecosystems. Hydropower is one of the main culprits. While being promoted as a carbon free source of renewable energy, hydropower disrupts the flow, habitats, and biota of rivers. Environmental policies and programs seek to mitigate the damage hydropower causes. Any policy action aiming at making the utilization of our rivers more sustainable must be ecologically, economically, and legally feasible. We show that the interdisciplinary feasibility of mitigation measures divides existing facilities into three categories (i) large facilities in which biodiversity mitigation measures are needed but electricity generation and balancing the electricity grid should remain as their main focus, (ii) small facilities in which dam removal and full scale river restoration measures can be taken by assisting the facilities to seize operations, preferably just before their next big investments, and (iii) medium facilities where benefits and trade‐offs associated with alternative paths should be analyzed case‐by‐case to determine the most feasible path forward. Policy action is feasible in all three categories but in different ways: requiring fish passes in the case of large facilities, helping remove dams and restoring the rivers in the case of small facilities, and focusing cost–benefit analysis efforts on the non‐trivial group of the medium sized facilities.

Evaluation of water quality using water quality index, synthetic pollution index, and GIS technique: a case study of the river Gomti, Lucknow, India.

The river Gomti, one of India's most polluted rivers, passing through Lucknow, Uttar Pradesh, India, has been selected for this study. An attempt has been made to assess its water quality status by combining the water quality index (WQI) and synthetic pollution index (SPI). Further, the data integration with the geographic information system (GIS) along with twelve water quality parameters for the seven sampling stations (S1 to S7) over 5years (2013-2017) has been performed. The study area showed a variation of WQI from 78.993 to 249.388 and SPI from 0.868 to 2.096 in 5years. The map interpolated through GIS revealed that the WQI falls into the category of severely polluted (76-100) and unsuitable for human consumption (> 100), while SPI lies in the category of moderately polluted (0.5-1.0) and severally polluted (1.0-3.0). The BOD and COD were found to significantly influence the WQI and SPI scores. With the constant release of waste effluents into the river, all selected parameters increased from S1 to S7. Based on the study, effective wastewater management is immediately required to improve water quality and support any sustainable river restoration plan.

Flood Routing Model Coupled with Dynamic Leakage Losses for Ephemeral Rivers with Large Potholes.

Ephemeral rivers commonly occur in regions with a shortage of water resources, and their channel configuration tends to change substantially owing to long drying times and artificial sand extraction. During short-term water conveyance, water storage in large potholes and leakage along the dry riverbed retards the flow, which is detrimental for the river landscape and ecological water demand. The objective of this study is to evaluate the flow process corresponding to a certain release scheme. A coupled dynamic leakage loss and flood routing model was established to predict the flood routing distance for dry rivers with potholes and strong leakage. The model mainly includes three sub-models of flow dynamics, dynamic leakage loss and water balance along multiple cross sections of the river channel. The water head was dominated by flow velocity and the overflow from potholes. The model was applied to Yongding River, a typical ephemeral river in northern China, and the model parameters were calibrated and verified using monitoring data from ecological water releases into the Yongding River in 2019 and 2020, thus, making the model more stable and reliable. Finally, the model was used to evaluate the impact of cross section optimization and pothole treatment on the flow process. This study can provide scientific guidance for ecological water conveyance and the ecological restoration of ephemeral rivers.

A possible role for river restoration enhancing biodiversity through interaction with wildfire

AbstractBackgroundHistorically, wildfire regimes produced important landscape‐scale disturbances in many regions globally. The “pyrodiversity begets biodiversity” hypothesis suggests that wildfires that generate temporally and spatially heterogeneous mosaics of wildfire severity and post‐burn recovery enhance biodiversity at landscape scales. However, river management has often led to channel incision that disconnects rivers from their floodplains, desiccating floodplain habitats and depleting groundwater. In conjunction with predicted increases in frequency, intensity and extent of wildfires under climate change, this increases the likelihood of deep, uniform burns that reduce biodiversity.Predicted synergy of river restoration and biodiversity increaseRecent focus on floodplain re‐wetting and restoration of successional floodplain habitat mosaics, developed for river management and flood prevention, could reduce wildfire intensity in restored floodplains and make the burns less uniform, increasing climate‐change resilience; an important synergy. According to theory, this would also enhance biodiversity. However, this possibility is yet to be tested empirically. We suggest potential research avenues.Illustration and future directionsWe illustrate the interaction between wildfire and river restoration using a restoration project in Oregon, USA. A project to reconnect the South Fork McKenzie River and its floodplain suffered a major burn (“Holiday Farm” wildfire, 2020), offering a rare opportunity to study the interaction between this type of river restoration and wildfire; specifically, the predicted increases in pyrodiversity and biodiversity. Given the importance of river and wetland ecosystems for biodiversity globally, a research priority should be to increase our understanding of potential mechanisms for a “triple win” of flood reduction, wildfire alleviation and biodiversity promotion.

Freshwater fish biodiversity restoration in floodplain rivers requires connectivity and habitat heterogeneity at multiple spatial scales

With a sixth mass extinction looming and freshwater biodiversity declining at unprecedented rates, evaluating ecological efficacy of river restoration efforts is critical in combatting global biodiversity loss. Here, we present a comprehensive study of the functioning for fishes of 46 river restoration projects in the river Rhine, one of the world's most heavily engineered lowland rivers. Floodplains with permanent, either one- or two-sided lateral connectivity to the main channel, favour total fish abundance, and are essential as nursery areas for riverine fishes. Habitat heterogeneity had a strong positive effect on species richness but was negatively related with fish abundances. However, the effects of environmental variables varied between ecological groups and spatial scales. Surprisingly, richness of critical rheophilic fishes declined with large-scale habitat heterogeneity (~1000 m), while it increased at small scales (~100 m), possibly because of the presence of unfavourable habitats for this ecological group at larger scales. Clearly, there is no one-size-fits-all design for river restoration projects. Whether a river section is free-flowing or impounded dictates the scope and efficacy of restoration projects and, within a river section, multiple complementary restoration projects might be key to mitigate freshwater fish biodiversity loss. An essential element for success is that these projects should retain permanent lateral connection to the main channel.

Hydrological simulation and assessment of the optimal parameters of the water replenishment of the floodplain lake and old riverbed on the Uzh river

One of the tasks in modern approach of the water resources management is improving environment health by the way of the river restoration. On the urban area it is impossible to provide full river restoration, but at the same time it is possible to create the environment close to natural. In our work on the example of the river Uzh located inside the city provides the assessment of the restoring possibility of the part of the floodplain by water replenishment of the old riverbed during the vegetation season. Flood control dyke construction interrupted the connection between old riverbed and river and as a result floodplain lake became muddy, silted up and lost its attractive form. To assess the possibility of the floodplain lake replenishment, the simulation of some scenarios were carried out: natural condition, water replenishment during flood, pumping water, raising water level in the river Uzh near the lake. The connection of the lake and the old riverbed with the river will improve slightly the storage capacity of the lake and allows to provide the depth of up to 1.0 m in the lake during flood, but the water will be absent in the old riverbed during the dry season. Hydraulic calculation showed that replenishment during spring floods and pumping water were not possible due to high hydraulic conductivity of the gravel and pebble soils. The old riverbed replenishment is possible by raising water level in the river Uzh, which will ensure the free water flow into the lake and into the old riverbed during the dry season.

How do geomorphic characteristics affect the source of tree water uptake in restored river floodplains?

AbstractAlpine rivers and their floodplains have been highly modified by human activities during the last decades. River restoration projects aim to counteract these negative impacts and to restore ecosystem services provided by riparian habitats. We studied two recently restored river sites in the Ahr/Aurino and Mareit/Mareta Rivers (Italian Alps) to investigate how geomorphic conditions, soil moisture, and groundwater level affect the source of water used by grey alder (Alnus incana (L.) Moench). We compared the isotopic composition (δ2H) of tree sap at different locations (low terraces formed during bed incision and recent floodplains formed after restoration) with that of potential water sources, that is, groundwater, soil water, and rainfall. The monthly variation in the isotopic composition of rainfall was reflected in both shallow and deeper soil water, as well as in the isotopic composition of sap. The redistribution of precipitation and groundwater in the soil differed between the post‐restoration floodplain sites and the post‐incision terraces, leading to a different relation between the sap water, soil water, and groundwater isotopic composition. The results show that transpiration of A. incana trees growing on recent floodplains is mostly supported by stream‐fed soil water, whereas trees growing on terraces mainly use precipitation‐fed soil water. These marked, morphology‐related differences in the source of transpiration water of grey alder highlight how channel degradation still affects the ecohydrological processes in Alpine fluvial corridors. Nonetheless, large restoration interventions—in terms of channel widening—can enable the self‐formation of new floodplain areas characterized by stream water‐fed riparian ecosystems.

Integrating geospatial techniques and field survey to assess the changing nature of meander movements and meander geometry of Raidak-I River in the Himalayan foothills, West Bengal

Channel migration and resultant meander movements are the two important fluvial processes found in the riparian environment of a river basin. The present research explores the changing nature of the meander movements and meander geometry of the Raidak-I River in the Himalayan foothill region using geospatial tools. The study incorporated Landsat data (satellite imageries) for the years 1972, 1980, 1988, 2004, 2012 and 2021 and the whole study has been segmented into five periods i.e., 1972–1980, 1980–1988, 1988–2004, 2004–2012 and 2012–2021 to examine which type of meander movement dominates in the Raidak-I River within a particular time frame and how the nature of the meander movements is being changed over time. Bank lines of different periods have been superimposed with the help of the overlay analysis method in ArcGIS software (Version 10.8) to obtain the results. Furthermore, Arc-Extension tools have also been used to measure the meander geometry. Twelve active river bends have been identified to study meander geometry of sinuosity indices, meander length, meander width, meander-ratio, channel width and radius of curvature from 1972 to 2021. Initially, lateral movements predominated but, in the late-stage, rotational movement became much more prominent, which indicates dynamicity of the river channel in recent time. The cross-sectional study revealed that a convex bank has frequently been replaced with a concave bank and vice versa. The study finds human intervention – especially the construction of embankments – is the main reason behind such meander dynamics. The method we have used here is very simple, and thus can be considered for any part of the world and is very beneficial for identifying suitable sites for embankment construction, river restoration and channel management.

Surface water quality in the upstream of the highly contaminated Santiago River (Mexico) during the COVID-19 lockdown.

The Santiago River (Jalisco) is a major waterway in western Mexico and has received considerable attention due to its severe pollution. Understanding the impact of reduced human activity on water quality in the Santiago River during the COVID-19 lockdown (April–May 2020) is critical for river management and restoration. However, there has been no published study in this context, presenting a significant knowledge gap. Hence, this study focuses on determining if the nationwide COVID-19 lockdown influenced or improved surface water quality in a 262-km stretch of the Santiago River upstream. Data for 15 water quality parameters collected during the lockdown were compared to levels obtained in 2019 (pre-lockdown), 2021 (unlock), and the previous eleven years (2009–2019). The values of turbidity, BOD, COD, TSS, f. coli, t. coli, nitrate, sulfate, and Pb decreased by 4–36%, while pH, EC, total nitrogen, and As increased by 0.3–21% during the lockdown compared to the pre-lockdown period, indicating a reduction in organic load in the river due to the temporary closure of industrial and commercial activities. An eleven-year comparison estimated a 0–38% decline in pH, TSS, COD, total nitrogen, sulfates, nitrates, and Pb. The unlock-period comparison showed a significant rise of 3–37% in all parameters except As, highlighting the potential repercussions of restoring activity along the Santiago River. Estimated water quality indices demonstrated short-term improvements in river water quality during the lockdown when compared to other time periods investigated. According to factor analysis, the main pollution sources influencing river water quality were untreated household sewage, industrial wastewater, and agricultural effluents. Overall, our analysis showed that the COVID-19-imposed lockdown improved the water quality of the Santiago River, laying the groundwork for local officials to identify pollution sources and better support environmental policies and water quality improvement plans.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12665-022-10430-9.

Dryland river restoration via carnivore reintroduction: Nonnative fauna dominate diets of river otters reintroduced to the Upper Rio Grande

Dryland rivers often harbor abundant populations of nonnative species that threaten native fauna and negatively alter ecosystem structure and function. Native semiaquatic carnivores, such as river otters (Lontra canadensis), that could predate nonnative fauna have been extirpated from many dryland rivers. During 2008–2010, river otters were reintroduced to the Upper Rio Grande (URG), a principal dryland river in the arid southwestern USA that has been colonized by dozens of nonnative fish and invertebrates. We conducted a scat-based food habits study and investigated whether otter reintroduction could be useful for managing nonnative aquatic fauna via predation. Across seasons, nonnative crayfish and fish were the dominant prey items in otter scats; crayfish frequency of occurrence was highest (61–95%), followed by nonnative suckers (7–26%) and trout (3–28%). After accounting for heterogeneous sampling effort between seasons, multi-level models estimated 0.77–0.93 probabilities that scats contained crayfish, compared to 0.05–0.21 and 0.03–0.14 probabilities for suckers and trout, respectively. Reintroducing river otters, and possibly other semiaquatic carnivores, to degraded dryland rivers might be an effective conservation action for controlling nonnative faunal populations within the biomic approach to river restoration, which could reestablish trophic cascades that improve ecosystem structure and function.

Initial ecological restoration assessment of an urban river in the subtropical region in China

Rivers in urbanised cities are often polluted, black, and odorous, with poor water quality and deteriorated ecology. Despite many river restoration studies, assessments of ecological responses to river restoration practices remain scant. Benthic animals are useful biological indicators showing the change and succession of river ecosystems; however, previous studies have mainly focussed on a few target species without considering overall ecosystem integrity. Here, we used a multi-index biological assessment method, benthic index of biological integrity (B-IBI) to assess ecological responses to river restoration of the Shahe River in subtropical region of China. Spatiotemporal changes in the macrobenthos community structure after restoration were monitored to explore species succession. We found that the number of macrobenthos species increased from 16 to 42, with the emergence of some pollution-sensitive species during the restoration period. Molluscs showed widespread recovery, and their relative proportions almost doubled from 12.5% to 24.4%. Oligochaetes and chironomids were the pioneer species in the recovering communities, while gastropod molluscs and pollution-sensitive aquatic insects were transitional species that first settled during the initial recovery period. Based on our survey data, 25 candidate metrics were selected, and five core metrics (total taxa, Simpson diversity index, percentage of crustaceans and molluscs, percentage of predators, and percentage of collector-gatherers) were identified after screening to establish the B-IBI. Our analysis revealed a distinct improvement in the overall health of the river, with the proportions of “excellent” and “good” sites increasing from zero to 28.6% and from 14.3% to 42.9%, respectively. A correlation analysis indicated that water flow, molluscs, and total phosphorus content were the three drivers of ecological recovery in the Shahe River. Overall, our study demonstrates the importance of governance and restoration of rivers in tropical and subtropical cities, and provides valuable evidence that can guide the design and evaluation of river restoration works.

Response of macroinvertebrate community to water quality factors and aquatic ecosystem health assessment in a typical river in Beijing, China

Healthy aquatic ecosystems can offer basic ecological services for the sustainable development of humans and society. Water quality greatly influences the macroinvertebrate community in aquatic ecosystems and can alter the aquatic ecosystem's health status. However, the quantitative relationship between macroinvertebrate community and water quality factors in rivers remains unclear, particularly in urban rivers, which are strongly affected by human activities. Therefore, a new framework for the quantitative analysis between macroinvertebrate community and key water quality driving factors was developed in the study, meanwhile, the aquatic ecosystem health conditions were evaluated and validated by different methods. The framework was applied to a typical urban river, the North Canal River, which is regarded as the “mother river” of Beijing. Combined with the redundancy analysis (RDA) and the threshold indicator taxa analysis (TITAN), the water quality driving factors and their indicator species were identified and the corresponding response threshold was determined. Based on the benthic index of biotic integrity (B-IBI), the multi-metric rapid bioassessment method, and the biological monitoring working party (BMWP) score, the aquatic ecosystem health condition in the basin was comprehensively evaluated. The results show that fluoride, biochemical oxygen demand, ammonia-nitrogen and total phosphorus were the key water quality driving factors influencing the community structure of macroinvertebrates. Four indicator species of ammonia-nitrogen were identified by the TITAN method with a threshold range of 1.09–6.94 mg L−1, and three indicator species of total phosphorus were identified with a threshold range of 0.48–1.27 mg L−1. According to the results of the aquatic ecosystem health assessment, the river ecosystem was generally unhealthy and the upstream was better than downstream; the health condition in the mountainous areas of Changping district was the best, while that in Chaoyang district and the central city area was the worst. The framework could provide a strong basis for ecological restoration and pollution control of the urban rivers and become an important tool for the rehabilitation of aquatic ecosystems.

Fish Habitat Reclamation Based on Geographical Morphology Heterogeneity in the Yangtze River and the Short-Term Effects on Fish Community Structure

Human alterations, such as hydropower development, are intensive and have negative impacts on fish and ecological environment. However, fish habitat restoration projects based on geographical morphology have not yet been reported in the Yangtze River. To explore engineering measures used to restore fish habitat structure and function, a mesoscale fish habitat restoration project was designed and constructed, which included restructuring of habitat topography in the fluctuating area. Three-dimensional computational fluid dynamics (CFD) models were used to simulate and predict the project’s effect on the hydromorphology prior to construction, and an Acoustic Doppler current profiler (ADCP) was deployed to test and verify actual flow field improvement. Short-term effects on fish species sorting and their main ecological traits were examined. The results showed that vorticity and flow heterogeneity in the river reach increased, suggesting that the restoration projects created flow conditions favourable to indigenous fishes. Thus, pre-optimization using computer simulation is an essential and scientific procedure that could be used to increase the probability of river restoration success. The promotion of habitat diversity had strong effects on fish aggregation, especially for the rare and endemic fish species targeted. Fish abundance, catch biomass and species richness increased by 98.1%, 62.7% and 22.5%, respectively. There were significant differences (p < 0.05) in species number and catch abundance before and after the project. The number of rare and endemic fish species increased from four to nine species. Overall, this research provides evidence that the promotion of habitat hydraulic morphology heterogeneity accelerates the recovery of fish diversity and biomass.

The Dutch Rhine branches in the Anthropocene – Importance of events and seizing of opportunities

The Rhine branches in the Netherlands have been profoundly altered by human interventions in the past 2000 years. Three examples are elaborated to show that these alterations often result from specific events and the seizing of opportunities: the creation of a new Rhine bifurcation at Pannerden, the Room-for-the-River programme, and the mitigation of riverbed scour in the Rhine-Meuse estuary. This makes historical inquiry one of the keys to understanding geomorphological developments in the Anthropocene. For river restoration it holds the lesson that plans can be prepared in ordinary times and then be implemented at the right moment by seizing the opportunities offered by events.

Lower Havelniederung - Most Significant River Restoration Project in Europe

Lower Havelniederung - Most Significant River Restoration Project in Europe

Morphological adjustments of the lower Orba River (NW Italy) since the mid-nineteenth century

A multi-temporal and multi-scale analysis based on historical data collection and review, maps and aerial photograph interpretation, field observations, topographic surveys, and GIS investigations was performed to (i) examine the morphological evolution of lower Orba River since the mid-nineteenth century, (ii) identify its controlling factors, and (iii) correctly interpret ongoing hydrogeomorphic conditions under a river management perspective. The riverbed experienced overall slight and non-homogeneous morphological adjustments, along with some horizontal displacements, up to the early twentieth century (Phase 0). Subsequently, two phases of channel degradation were identified. The first, from the 1920s to the 1950s (Phase 1), is characterized by slight narrowing (12.3%), the beginning of incision, and rare and little lateral migration. The second, between the 1950s and the years around 2010 (Phase 2), displays significant channel incision (mostly from the 1950s to the 1970s, from 0–1 m to 4–5 m), weak narrowing (21.0%), and only minor horizontal displacements. Over the last decade (Phase 3), widespread slight channel widening (3.4%, up to 25.7% at the reach scale) associated with the absence of a generalized bed-level variation trend was observed. The study reach has exhibited a single-thread or transitional channel since the mid-nineteenth century. Channel incision was mainly caused by extensive in-channel sediment extractions primarily carried out between the 1950s and the early 1980s at the reach and catchment scales. The long-term presence of widespread channelization works was recognized as the main reason why overall little riverbed planform adjustments occurred during the whole period investigated. The most recent dynamics were triggered by floods and were interpreted as the river response to human-induced alterations. The riverbed changes that occurred during the twentieth century match the channel adjustments commonly experienced by Italian single-thread and transitional channels as a response to various types of human disturbances. However, the detected morpho-evolutionary phases of the Orba River are only partially in agreement with those reported in the literature for other Italian rivers affected by similar anthropogenic pressures, as some differences exist in timing and magnitude of prevalent channel adjustments. An overall slight potential for channel recovery, priorities for rehabilitation, and the main objectives for the next-decades management were identified. This research provides insights into the medium- and short-term morphological evolution of Italian rivers, and its outcomes represent an essential piece to drive river management towards sustainable and effective river restoration and risk mitigation measures framed within a larger, multidisciplinary, and objective-based context. A wide spectrum of both consolidated and newly developed GIS-based planform metrics was considered to assess the channel morphological evolution in detail, providing an operative reference framework for future investigations.