Hydro-morphodynamic connectivity and ecosystem design in a changing environment

This joint Sino-German research project is funded by the DFG and the NSFC in the framework of long-standing efforts to foster scientific collaboration between China and Germany. More information on funding sources will be available on the DFG’s GEPRIS platform.

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Fig. 1 The Rhine in Germany on the left (image: Sebastian Schwindt, 2016) and the Yellow River on the right (image source: Jin Zhang/Xinhua News Agency, 2016).

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Motivation

Water resources engineering fragmented many rivers on earth and disrupted the continuity of aquatic ecosystems. The Yellow River in China and the Rhine in Germany emblematically testify the evolution that came along with industrialization in the last two centuries. The landscape around the two rivers changed from braided and varied pattern to monotonous navigable streams, which are split by multi-purpose dams. In the coming decades, global change is expected to enhance the destruction of aquatic habitats even more with severe consequences for the food security. Thousands of river restoration projects are currently in progress worldwide to mitigate the risks of ecosystem loss and global change. However, the communication between different domains of expertise and also between regions is often lacking. This project is building green bridges between hydrologists, engineers, ecomorphologists, as well as between China and Germany. Hydrological analyses of fluvial landscapes will be performed to guide ecologically friendly dam releases and river restoration actions toward robustness against global change.

Collaboration & Goals

The collaboration of the Chinese North China Electric Power University (NCEPU) and Yantai University (YPU) with the German University of Stuttgart will leverage the establishment of a two-fold approach in two different environmental setups. The two-fold approach involves a hydrological optimization of ecological sustainable dam releases by the research team based in China and an ecomorphological design optimization for river restoration performed at the University of Stuttgart. The project profits from prior studies on the Yellow River and the Rhine conducted by the two research teams. Both rivers created morphologically similar fluvial landscape pattern, but in hydrologically and geologically different environments and different legacy.

Methods Overview

This project uses data from both the Yellow River and the Rhine to optimize hydrological connectivity and sustainable ecosystem restoration actions. The role of computers in the design of ecosystems has become increasingly important in recent years and powerful numerical models have now set the standard for planning interventions at rivers. However, objective, parametric descriptions of fluvial landscapes are lacking. Such parameters are required to sustainably design ecosystems for target species in a changing climate. This project takes up the challenge of defining relevant hydrological connectivity and morphodynamic parameters to manage and re-design fluvial landscapes sustainably. The parametric description of fluvial ecosystems will enable a unique coupling of numerical modelling and new river design algorithms via feedback loops. Such feedback loops will involve hydro-climatic regimes and ecomorphological connectivity parameters. This Sino-German collaboration will endow its results with global relevance by merging expertise and complementary hydrological-morphological analyses.

Background

Affected by global change and multiple stresses of human activities, such as dam construction, channelization, and urbanization, 47% of the earth’s surface has experienced irreversible changes [1], [2]. For example, more than three thousand dams fragment the Chinese Yellow River watershed and hinder fish migration [3]. On the other side of the world, the German Rhine was “corrected” for navigation purposes already at the beginning of the 19th century [4] with dramatic consequences for the aquatic ecosystem [5], [6]. While energy production and agriculture still depend on past river “corrections”, their impacts on the ecosystem increasingly endanger food security. In addition to the anthropogenic influenced changes (legacies) of rivers, the predicted hydro-climatic change is expected to amplify the stress on flora and fauna [7]. The Yellow River and the Rhine represent two characteristic waterways with legacy that had devastating consequences for the fluvial ecosystems. Their legacies and the hydro-climatic change will impose similar challenges in both watersheds, where extended drought periods and intensified floods are expected [8]. However, the sustainable employment of hydrological control structures (e.g., dams) and nature-based engineering can mitigate the consequences of the expected climate change. Large dams at the Yellow River provide storage capacities that enable the imposition of so-called “environmental flows”, which describe quantities, quality and pattern of discharge fluctuation required to sustain fluvial ecosystems [9]. In the absence of storage capacity for environmental flow control, fluvial ecosystems can be sustained through direct, local measures on the river reach scale (~up to 100 channel widths). Such measures involve terraforming and nature-based engineering features with indigenous vegetation and aim at the simultaneous enhancement of aquatic habitat and flood safety [10]. Both the Yellow River and the Rhine were subject of many scientific studies and this project aims to combine existing and new findings from both fluvial environments. A team of leading researchers based at the North China Electric Power University (Beijing) and Yantai University (Yantai) focused their research on the ecosystem of the Yellow River. The researchers found, for example, that since the construction and operation of the 154-m tall Xiaolangdi dam in the lower reaches of the Yellow River in the year 2000, original habitats were destroyed, the fish population reduced by more than 50% and the abundance of phytoplankton as well as zooplankton reduced by 60% and 88%, respectively [3]. The dam construction particularly endangers mollusks, benthic fish and zooplankton [11]. Also the wetlands of the Yellow River are affected by Xiaolangdi dam and studies have shown that the compensation for wetlands loss amounts to 66 million yuan per year (~8.5 million EUR) [12]. In addition to damming, global warming has led to drastic changes in the water cycle, with significant alterations of runoff pattern and increased extreme hydrological events in the region. Today, the runoff of the Yellow River has disproportionally decreased compared with the sediment discharge. While extreme flood and drought events both have occurred more frequently, the total runoff of the Yellow River into the Bohai Sea has decreased by 50% which can be attributed to a regional decrease in precipitation [13]. Reservoir management with ecologically beneficial discharge hydrographs and environmentally friendly sediment flushing are potential solutions to recover the ecosystem at the Yellow River. However, the prior characterization of dynamic, self-maintaining, and regenerating “healthy” habitats in the Yellow River is necessary. In general, a “healthy” river state is described by hydraulic, ecological, and morphological diversity [14], which can also be parametrically expressed [15]. Several approaches exist for the parametric description of hydrological and morphodynamic healthy ecosystems, but they often imply subjective expert assessments. Researchers from the University of Stuttgart have conducted comprehensive studies on parametric and objective ecosystem assessments to reduce vulnerability caused by subjective assessments. The researchers used for example structure-from-motion [16], biological index-driven habitat analyses [17], [18], fuzzy logic [19], [20], and numerically driven river restoration feature planning [18], [21]. Numerical modelling plays a key role in the parametrization of fluvial ecosystems and the group of researchers around Prof. Silke Wieprecht (Institute for Modelling Hydraulic and Environmental Systems IWS at the University of Stuttgart) set benchmarks in hydro-morphodynamic modelling in combination with habitat suitability modelling [17], [20], [22]. However, the translation of morphodynamic modelling and ecosystem characterizations into the generation of new aquatic habitats represents a great challenge for researchers worldwide. The collaboration of researchers from China and Germany has the potential to leverage this challenge with their expertise in eco-hydrology and ecomorphology, respectively. To enable this collaboration, the Rhine offers suitable study sites in Germany for knowledge transfer from and to the Yellow River in China. The knowledge transfer becomes possible and meaningful because of similarities in the fluvial landscape pattern, but interesting dissimilarities in the river’s sediment budget as an artefact of two different hydro-geological environments. Table 1 lists the main differences between the Yellow River and the Rhine, which will enable complementary insights to broaden the significance of the project results to many other rivers in the world.

Table 1: Comparison of the framework and legacies at the Yellow River and the Rhine.

River feature

Yellow River

Rhine

Channel bed

Aggrading (sediment surplus)

Incising (sediment deficit)

Channel banks

Increasingly rigid (engineered)

Rigid with local scarification in progress (restoration projects)

Floodplains

Subject to current industrial development

Industrial legacy

The highly erosive watershed of the Yellow River and sparse vegetation supply much sediment that causes sedimentation problems in downstream river reaches. Even though the Yellow River is strongly modified by dams, large amounts of fine sediment are still transported and deposited in downstream reaches (corresponds to a transport-limited-system with sediment surplus). In contrast, the Rhine is a sediment supply limited system (because of multiple dams in the river course) and requires thousands of tons of sediment injections every year to sustain its geomorphic stability [23]. The latest engineering efforts in China aimed at reinforcing the river banks to prevent flooding of the alluvial plains of the Yellow River, whereas restoration efforts at the Rhine currently scarify rigid banks more and more in river reaches where navigation is not affected [24]. The restoration efforts at the Rhine follow a two-century long industrialization with sealing of natural grounds and channelization that damaged the fluvial ecosystem and simultaneously increase navigation as well as flood safety [25]. In the framework of restoration efforts at the Rhine, the IWS has had the opportunity to perform several research projects in the last decades. Table 2 chronologically lists the most recent projects with resulting data products at the Rhine. Figure 2 maps the position of the IWS projects at the Rhine.

From 2013 to 2017, the IWS (University of Stuttgart) analyzed sediment cores at the Upper Rhine between the barrages at Marckolsheim and Rhinau at the French-German border [26] down to Iffezheim [27]. The sediment cores were examined in the so-called SETEG flume and a highly sophisticated measurement method, called PHOTOgrammetric Sediment Erosion Detection (PHOTOSED) [28]. The SETEG flume and PHOTOSED method determine the depth-dependent erosion stability and the critical bed shear stress [29]. In addition, the sediment core samples provide data on grain size, bulk density, biological substrate characteristics, and contaminates. These data represent valuable input for this collaborative project, where numerical models may be build, calibrated, and validated with the information on bed shear stress and grain size distributions. Moreover, the sediment and water probes provide data on suspended and bed load of the Upper Rhine.

Since 2019, the IWS is investigating the evolution of water depths of the Rhine in the context of river engineering interventions since the early 19th century, which aimed at improving the navigation conditions on the river [4]. The engineering actions caused channel erosion and deteriorated the ecological state of the Rhine. Further engineering interventions have been carried out more recently with the goal of improving the ecomorphological condition of the Rhine again. In particular, the IWS studies the effects of hydraulic engineering structures (e.g., longitudinal and transverse structures such as dikes) and ecological measures on the hydraulics of the Rhine within the framework of a project funded by the German Federal Institute for Hydraulic Engineering (BfG). Through the project with the BfG, the IWS has access to large amounts of data from the BfG with information on hydraulic structures, hydrological analyses, riverbed elevations and water levels. The result of the BfG project includes a detailed student project that documents engineering interventions at the Upper, Middle and Lower Rhine between Lake Constance and the estuary in the Netherlands [30]. These data and the literature review will be available for this collaborative project. An additional collaborative project with the BfG is currently under preparation to investigate hydro-morphological indicators that classify both natural and strongly impaired water bodies regarding the habitat suitability.

Objectives

This project seeks a multi-objective river ecosystem design model to meet the needs of river health and socioeconomic development in the light of global change. It focuses on exploring the response relationship of hydro-morphodynamic river ecosystem adjustments and how those can be optimized to mitigate hydro-climatic change. The global objective is to establish robust hydrological and hydro-morphodynamic design schemes for the adaptation of fluvial ecosystems to attenuate impacts caused by extreme droughts and floods. This superordinate objective is achieved by breaking it down to three specific objectives.

Objective 1: Synthesize Existing Methods

The first sub-objective consists of a synthesis of existing methods and data for ecosystem enhancement. The focus will be on hydrological, hydraulic, and morphodynamic parameters (including connectivity characterizations) and approaches. Within the first year, the comprehensive literature review and data assessment produces a river database of hydrological, hydraulic, ecological, and morphodynamic parameters characterizing both the Yellow River and the Rhine.

Objective 2: Generate Novel Models

The second sub-objective is a parametric, morphodynamic optimization of fluvial landscapes. The research team based in China optimizes fluvial ecosystems by adjusting discharge hydrographs (e.g., by imposing environmental flow schedules) to build a hydrological connectivity optimization scheme. At the University of Stuttgart, we focus on morphological adaptations such as resilient, adaptive terraforming and nature-based engineering. The optimization aims at the application of parametric characteristics of high quality aquatic habitat previously identified in the literature (first sub-objective) to build a morphodynamic ecosystem optimization scheme.

Objective 3: Integrate Novel Hydro-Morphological Models

The third sub-objective is to combine and test our jointly developed design schemes and algorithms for hydro-morphodynamic optimization and hydrological connectivity of aquatic habitat. The tests include the previously defined hydro-climatic change scenarios (longer drought periods and amplified floods). Moreover, we develop programmatic tools that can be used in central Europe as well as in Asia for the development of ecologically healthy rivers under different constraints and hydro-climatic uncertainty. Thus, we consider the different environmental constraints at the Yellow River and the Rhine (see table top of the page). We analyze the preparedness of rivers for hydro-climatic change scenarios with the constraints of different sediment budgets (aggrading or incising rivers), and different degrees of freedom for instream and floodplain river restoration (flow regulation or morphological impairment).

Work program & Principle

Milestones

The three-years work program starts in 2021 and annual milestones are to planned to be implemented for achieving the three objectives:

    1. GET STARTED

    • Literature review

    • Data acquisition & creation of a database

    • Model preparation

    1. GENERATE MODELS

    • Decision on hydro-climatic scenarios (based on literature and data review)

    • Development of an ecomorphodynamic optimization scheme (team IWS)

    • Development of an eco-hydrological connectivity optimization scheme (team NCEPU/YPU)

    • Deliverables: Morphodynamic and hydrologic connectivity ecosystem optimization

    1. SYNTHESIZE & TEST MODELS

    • Aggregation of eco-hydrological and ecomorphodynamic optimization scheme

    • Model synthesis and publication of digital products

workflow

The first project phase involves a detailed literature and data review. The literature review will focus on the ecosystem of the Rhine, its past evolution, target species and restoration activities. We will identify all possible data resources (e.g., flow series, hydraulic data, habitat suitability curves, substrate classifications, and existing terrain models), which are needed for numerical models of the Rhine and ecosystem optimization algorithms. An analysis of the hydro-climatic environment of the Rhine will mostly use existing data and classifications of the current flow regime, as well as an assessment of hydro-climatic change scenarios with their consequences for extreme hydrological events. The hydro-climatic analysis will consider extreme events in the shape of extended drought periods and amplified flood events. During longer periods of drought, lateral riparian habitats are expected to dry out. In contrast, during major flood peaks, greater hydraulic forces must be assumed, which can have destructive effects on habitats. Our project partners from the North China Electric Power University (NCEPU) and the Yantai University (YPU) will perform a similar literature review on the Yellow River. However, while we are looking at possibilities to optimize fluvial landscapes, the NCEPU/YPU research team in Beijing will investigate ecosystem improvements through modifications of discharge releases from dams (hydrological connectivity optimization). Their literature review encompasses the spatio-temporal evolution of hydrological connectivity, the assessment of climate change scenarios and human impact on the Yellow River basin, and the analysis of the current longitudinal hydrological connectivity of the Yellow River. Based on the available datasets, we identify two to three study sites at the Rhine, each about 2-3 km long, which we then model numerically. After the establishment and the numerical, hydraulic-morphodynamic modelling of the current state of the selected sites, we improve and newly develop landscape modelling schemes and algorithms (e.g., similar to River Architect [18]) to enhance the habitat quality for target species. We identify climate change scenarios and agree on relevant scenarios within the entire Sino-German research team. The climate change scenarios constitute alternate (drought and flood) hydrographs (upstream boundary conditions) that we are modeled with a current-state morphology. With the model results, we analyze how river landscapes can be modified to provide robust habitat in the case of prolonged drought and emphasized floods. The researchers based in China have already developed models and methods needed for the numerical and physical analyses of the Yellow River in the past. The study on the Yellow River contributes the hydrological counterpart to our morphodynamic optimization. As a result, the Chinese research team will benefit from the morphodynamic ecosystem optimization scheme produced by the IWS and the IWS will benefit from the hydrological connectivity model elaborated by the Chinese research team.

Software

We use exclusively open-access and open-source software for the following purposes:

Moreover, we have a strong commitment to open-access publishing of any results. All codes and algorithms will be provided on publicly available git repositories and referenced on this website at the time of publishing.

Instructions for getting ready to use models, codes, and algorithms provided are available at the online learning platform hydro-informatics.github.io, which represents the baseline for online teaching contents of IWS’ hydro-morphodynamics research group

References

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