Eco-restoration of Rivers

Abstract

Rivers, the fluvial landscape enabled both ancient and modern societies to develop and flourish in the proximity of rivers which fundamentally shape the present earth with all its living and nonliving entities including human being. However, humans have spatially and temporally altered rivers since time immortal because of intensive use of the rivers for navigation, flood control, abstraction of water for drinking and agriculture, urbanization coupled with industrialization, disposal of wastes including sewage, thermal effluents, both nontoxic and toxic chemicals alongside river bed mining, dredging, and construction of dams, barrages, etc.

Large river systems all over the world have been extensively dammed for hydroelectric power, recreation, and flood control and to divert water to support agriculture which have caused not only massive alteration of habitats but led to the loss of fisheries and the ecological balance in the river ecosystem. The severity and extent of human-mediated eco-degradation and disturbances of the aquatic ecosystems have prompted to undertake corrective interventions, in order to restore or rehabilitate lost and/or damaged ecosystem functions. Recent interest in river restoration reflects a significant change in river managerial regimes.

It also reflects a wider fascination with “ecological restoration” in the scientific and technical literature and in public debates about approaches to environmental management. The concept of making or inducing positive changes in ecosystems is controversial, both in theory and practice. Restoration programs and relevant research projects are characterized by being one of the major goals, i.e., returning of the old so-called pristine normal environmental condition from its present degraded state of affairs. But such mission often contributes to develop sometimes conflicts with a number of other different purposes. Restoration projects involve surface and groundwater flow and quality regimes and focus on the impacts of those regimes on natural aquatic and terrestrial ecosystems as well as human economic and social “ecosystems.” Processes that control river ecosystems are hierarchically nested, both spatially and temporally.

Long-term geologic, tectonic, and climatic processes create the landscape template that controls the structure of river networks and valley forms, which are generally immutable over human time frames. The landscape template sets limits on the types of habitats and process rates that are expressed in river reaches, but watershed- and reach-scale processes control conditions at any point in time.

Runoff and erosion processes control stream flow and sediment supply, while nutrient supply processes control primary productivity at the base of the food web. Reach-scale processes, including routing of sediment and water, river–floodplain interactions, riparian processes, and instream biological processes control ecosystem conditions at the reach level. Human impacts to these processes include both indirect and direct effects on habitats and ecological systems. Indirect effects are those that affect processes away from the stream, such as land-use effects on erosion or runoff processes that ultimately affect stream flow or sediment supply, or riparian vegetation impacts that affect stream temperature or wood and nutrient supply. Direct manipulations of river channels and biota include impacts such as dredging or channel control structures or directs effects on biota such as fishing, hatchery practices, and stocking of non-native species.

Successful river ecosystem restoration is rooted in a clear understanding of linkages between causes of habitat change and the resultant effects of habitat change on biota and ecosystem processes. These cause–effect linkages are the foundation of process-based restoration, which aims to restore watershed and river processes that drive ecosystem functions and features. Process-based restoration is guided by four fundamental principles, including identifying major reasons for the change of habitat and ecosystem, involving local perspectives toward restoration actions, harmonizing scale of restoration with the ongoing biological and physical and biological processes, and explicitly stating expected outcomes.

The purpose of these principles is to guide river restoration toward actions that require minimal maintenance and create a resilient river system that adapts to future perturbations such as climate change. These principles also help define the needs of watershed assessments, inform how restoration actions should be identified and prioritized, support development and design of restoration projects, and guide the development of monitoring plans that track success or failure of projects. The present chapter has elaborately discussed multidimensional aspects of the science of restoration starting from the basic concept to its applicability and problems of implementation to different success stories citing several case studies.