River hydraulics, morphology, and vegetation (River HMV) are the key physical processes that govern the shape, size, and habitats of river systems. River hydraulics, refers the the mechanical properties of moving water and morphology describes how the landscape changes. Here, we include vegetation as it has significant impacts on both instantaneous and evolutionary hydraulic and morphologic conditions.
The complex interrelationship between River HMV processes has been studied for decades, yet they are still not well understood individually, let alone combined. What is known, is that when one or more of these processes is modified in river systems, the river and it's ecosystem will respond. World wide, the most prolific modifications to river systems include dams, irrigation draw, sediment mining, deforestation, and floodplain construction.
Whether for the protection of lives, property, or economical purposes, rivers have been heavily modified for township development, industries, water storage and hydropower, and farming.
Plagued by river modifications of the past, and facing a future of increased demand for water and energy, our rivers need restoration, protection, and innovations.
Over the past centuries, we have gained much knowledge on the environment and natures power. While we have historically tried to corral and command nature, we have time and again learned that our best designs and engineering have serious shortcomings - typically environmental degradation. We are currently seeing a greater awareness and respect for how nature got it right. As a result, new innovations and solutions to age-old problems are being tackled with new technologies that enable us to study nature better and new approaches that try to restore and mimic nature. Below, we discuss the innovative solutions that stand to best improve our current conditions.
New Technologies Furthering Our Knowledge
Data: Faster, Cheaper, and Sometimes Better. River restoration projects and research, like all land development projects, rely on topographic data. This has historically come from ground surveys and more recently by remote sensing from manned aircraft that produce digital elevation maps from technologies like LiDAR or Photogrammetry. In terms of applications available today, new methods of remote sensing are providing high resolution datasets at more affordable costs than were possible by previous platforms. These are in newly available software and hardware.
The adoption of geomatic technologies (e.g. GPS, LiDAR, etc.) has driven a profound increase in the dimensionality of topographic datasets and used within river science, and geomorphology more broadly. However, recent advances in computer vision and image analysis have led to a novel photogrammetric techniques called Structure-from-Motion (or SfM). SfM is a powerful tool as it has proven an effective tool to generate high-quality topographic elevation models at low-cost. This is exciting because researchers now can adequately and affordable capture terrain evolution over long periods of time, and practitioners have the ability to acquire current and relevant topographic data instead of relying on older datasets.
The most exciting new hardware are definitely Unmanned Aircraft Systems (UAS, UAV, or drones). The adoption of such systems offers affordable and high quality remote sensing. For example, drones have been shown to offer cost-effective solutions for data acquisition of aerial imagery for project base maps as well as the necessary images for SfM. However, these systems are capable of carrying far more than cameras payloads. UAS platforms are extremely exciting because we can now acquire data from various sensors while geo-locating the data (i.e. having GPS tied to individual data measurements). Further, we are seeing a revolution in the reduction of size, weight, and cost of popular sensors. For example, LiDAR is now available for as low as $85,000 (where manned aircraft LiDAR was easily around $1 million) and in complete turn-key packages weighing as little as 2.2 kgs. Thus such package are fully capable to be utilized by UAS platforms.
Each of these advances are now enabling all land development projects the capabilities to capture the data that they need at affordable costs. In turn, this quality data will enable managers the ability to make more informed decisions, higher detailed analysis, and overall better designs for functionality and sustainability.
Dams. Dams provide essential water supply for communities, but have caused significant river degradation due to interrupted sediment transport, reduced daily flows and periodic flooding, and consequently reduce available habitats for many species. However, smart planning and innovative sediment passage can vastly reduce the impacts.
Dams by Design, is the Nature Conservancy's approach to "reengineer old dams, remove or avoid others and better plan for those that will occur in the future" and for those that will be constructed, evaluating the "entire river basin and the impacts a dam will have both upstream and downstream" is conducted. Through these approaches, the nature conservancy found that 300,000 kilometers of river could be impacted by future hydropower; however, 100,000 kilometers could remain free flowing if designed appropriately (Rivers and Lakes: Hydropower by Design). Such benefits would drastically reduce the negative impacts, preserve valuable habitat, and through natural healthy rivers, excess nutrients can be further minimized.
Sustainability is a challenge for dams due to sediment trapping and storing which not only limits the working life of dams, but also starves and degrades rivers' downstream. Therefore, improving sediment transport through the dam, or in some cases around the dam, should be widely adopted. With proactive pre-planning of basin environment considerations, optimal dam site locations, design, and operations, sustainable dams can drastically reduce the environmental degradation and increase the longevity of the dams. Such forward thinking can make dams and reservoir storage capacity "viewed as a renewal resources, with much more positive implications for the future sustainability of water supply and hydroelectric generation" (Sustainable sediment management in reservoirs and regulated rivers: Experiences from five continents).
Vegetation as Engineers. Native vegetation plays a critical role in the evolution and physical shape and size of rivers. While many native vegetation has been removed from riverbeds, banks, and floodplains, restoration efforts are trying to re-establish such vegetation as a larger restoration project. However, many river restoration projects try to force specific conditions (e.g. a meandering pattern, pool-crest-pool profile, or river bank protection with boulders, etc.), where these 'designs' are often idealized or inappropriate for the hydraulics, morphology, or vegetation. Some new approaches use soft engineering, and rely on native vegetation to naturally help the river evolve into the healthy and sustainable system that the current conditions allow. Such methods simply re-introduce vegetation in appropriate areas (i.e. where the specific vegetation would naturally be found in relation to the river), let the vegetation thrive where the conditions are appropriate, and as a result the vegetation's presence will naturally evolve the river into the shape and size for the given conditions. While this approach is slower to reach aesthetically pleasing rivers, the final result is a river system that evolved to the governing conditions and is often cheaper due to less mechanical excavation and permitting. Further, the introduction of vegetation will have longer lasting eco-improvements, as the vegetation will naturally help filter and remove excess nutrients for the lands prior to entering the river as well as helping remove nutrients from the water.
New Management Tools
Over the last five years, several river restoration organizations have developed insightful tools to help during the process of river restoration. These range from a general lists of what river restoration looks like, to highly detailed step-by-step instructions. The latest is REFORM (REstoring rivers FOR effective catchment Management) which aimed to "improve existing tools and develop new ones to increase the success of cost-effectiveness of restoration measures" (REFORM). While focused on European rivers, the tools can be applied to any river restoration project where the rivers have been impacted by long-term modifications.
What is interesting in REFORM, is that the tool insists, and fully guides the practitioner, on assessing the larger set of spatial and temporal aspects that must be taken into consideration to better understand the current river system and what is reasonable to expect how the river can ‘naturally’ exist given the conditions.
“In assessing hydromorphology, to date there has been too strong a reliance on the reach scale, on the river channel and its current condition, and on focusing on specific river reaches in order to assess rivers, diagnose river problems and design intervention, rehabilitation and restoration measures.”
"The ways in which reaches of different type within a catchment have responded to changes / interventions in the past provides crucial information for forecasting how reaches may change in the future, whether the catchment continues to be used and to function as at present or to be subjected to different scenarios of change."
This well defined and presented methodology will help all river managers and restoration efforts into greater holistic views of the river systems, and hopefully greater sustainability in river projects.
Future Research: The science of river restoration in River-HMV is continually evolving and improving and we are constantly assessing the quality of restoration, the mistakes, and areas to improve. However, it is clear that many aspects in River-HMV are still noted as phenomena, as the full understanding of the mechanics is not well understood. Therefore research must continue and utilize i) laboratory experiments and field studies to quantify these process and better understand the processes, ii) numerical models need to be continuously developed and tested to best represent the physical conditions noted in the laboratory and field as well as using numerical models to test theories and examine processes at levels impossible in the field and laboratory both spatially and temporally, and iii) long term case studies are needed to evaluate our understanding by testing our theories and models capabilities. Indeed, this is an iterative process never likely to be fully satisfied, but gradually improved overtime and the benefits will be well worth the effort.
Videos To Watch
Articles and Links
Javernick, L., Brasington, J., Caruso, B. (2014). Modeling the Topography of Shallow Braided Rivers using Structure-from-Motion Photogrammetry.
- Gurnell, A. (2014). Plants as River System Engineers.
Natural, healthy rivers have been shown to better absorb excess nitrogen than unhealthy rivers. This is mainly due to the algae, fungi, and bacteria that thrive on the riverbed and rocks of the rivers, as well as the slower moving natural water, which have greater ability to absorb and utilize the available nitrogen. As these studies show, maintaining healthy rivers will promote healthier rivers, therefore, new approaches to mimicking healthy rivers is an important approach to 'jump-starting' a healthy river.
New studies are looking at how to maximize this exchange of nitrogen and the riverbed. Research on the Mississippi River, is looking at how to maximize exchanges between the water and riverbed. However, in many areas along the Mississippi River, fine sediment has deposited and restricts this exchange. Therefore, scientists are investigating how permeable bedforms on the riverbed might enhance mixing.