RIVER REHALIBITATION: LITERATURE REVIEW, CASE STUDIES AND EMERGING PRINCIPLES by *JM KING, #ACT SCHEEPERS, #RC FISHER, *MK REINECKE and #LB SMITH *Freshwater Research Unit, Zoology Department, University of Cape Town, Private Bag, Rondebosch 7701, South Africa # Department of Earth Sciences, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa Report to the Water Research Commission WRC No.: 1161/1/03 ISBN No.: 1-77005-098-1 DECEMBER 2003 Disclaimer This report emanates from a project financed by the Water Research Commission (WRC) and is approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the WRC or the members of the project steering committee, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. Executive Summary EXECUTIVE SUMMARY E1. Introduction Land and water developments worldwide have brought many benefits to humans, but also have led to a decline in the ecological form and functioning of rivers. There is growing realization of the national costs of poorly functioning rivers through, for instance, the decline of fisheries, the increasing need for expensive water-quality treatment, sedimentation of reservoirs, increasing severity of floods and flood damage, the need for expensive flood-control measures, the loss of recreational and biodiversity values, and much more. Because of this, rehabilitation of rivers is moving from a background of ‘grey’ science to a phase of increasing structure with a rapid build up of data and knowledge. This three-year project was planned to contribute toward the development of a South African pool of expertise on river rehabilitation. E2. Background to the study The Water Research Commission awarded separate contracts to the Freshwater Research Unit, University of Cape Town (UCT) and the Department of Earth Sciences, University of the Western Cape (UWC) to jointly run the project. Presented here is the joint final report. The overall approach was designed to: create formal research links between fluvial geomorphologists at UWC and freshwater ecologists at UCT; begin development of expertise in the field of river rehabilitation. Through a process of discussion with the steering committee, the project focused on the three following objectives: review of the world literature on river rehabilitation; completion of river-response studies on three Western Cape rivers where active river management was underway; derivation of a first draft of geomorphological and ecological principles for river rehabilitation. This report is divided into four parts. 1. Introduction 2. The literature review 3. The river studies 4. Conclusion, including derivation of emerging principles The project focused on physical aspects of river degradation and rehabilitation, whilst acknowledging that many other aspects, such as water chemistry and the legislative framework, would have to be addressed as part of a comprehensive strategy of river rehabilitation. i Executive Summary E3. The literature review Introduction There is no consensus internationally about what constitutes river rehabilitation or river restoration. The two terms are used loosely to describe a variety of projects with different goals. The ambiguity is largely a result of the value that different people place on the natural environment and what constitutes a natural environment. Proponents of the Balance of Nature paradigm believe restored river systems should be protected from outside (non-natural) human forces that change ecosystems, whilst those of the new Flux of Nature paradigm view ecosystems as continually disturbed, both by natural and anthropogenic forces, and responding to differing levels and different kinds of disturbance. In their view the biological constituents present in an ecosystem will not necessarily be the same as those in the future. Whichever view is held, there is a common goal of desiring to return a degraded river ecosystem to a more natural state. The underlying assumption behind almost all river rehabilitation projects has been that the re- introduction of a variety of physical habitats will improve the ecological functioning of a degraded ecosystem. Degradation of the river, however, could take many forms, and physical rehabilitation may not always be necessary or appropriate. Degradation of aquatic ecosystems Physical disturbance Physical disturbance of the river can result from human interventions either within the catchment or the channel. Two common channel disturbances are channelisation and canalisation. Channelisation involves straightening, deepening, widening or narrowing the channel, maintaining the banks in some desired (unnatural) form, or erecting embankments. Canalisation is an extreme form of channelisation, whereby the channel bed and banks are lined with concrete. The ecological repercussions of channelisation are many and complex, with a loss of heterogeneity that inevitably translates into a loss of ecological biodiversity. Hydrological manipulations Humans have intervened in all land-based parts of the hydrological cycle. Whilst dams represent the greatest intervention to rivers, inter-basin transfers of water (IBTs), direct abstraction, agricultural activities and urbanisation each have their own unique impacts. In general, these interventions have changed the pattern of high and low flows and sediment regimes of rivers, which have in turn led to changes in channel morphology, water quality and the biota. Abstraction rates from groundwater are also rapidly increasing worldwide. Generally, withdrawals from groundwater aquifers result in a lowering of the water table, a consequent reduction in stream flow, possibly with an intrusion of saline water, and so a decrease in water quality. The ecological effects of groundwater abstraction on riverine ecosystems are not well documented. Chemical disturbance Water quality naturally varies between rivers due to climate and the underlying geological formations, and through the year due to seasonal changes in flow and temperature and responding biological activity. Humans impact on water quality and quantity through changing drainage patterns to rivers and the chemical constituents and sediments the water may be carrying. They also use rivers as ii Executive Summary wastewater conduits and feed urban storm-water drains into them. Pollutants impact aquatic ecosystems by reducing abundances and biodiversity, and their general ability to function efficiently. Rehabilitation of degraded systems requires that attention be paid to the quality of the water, as well as the quantity and the physical attributes of the channel. Unless all three are suitable, planned rehabilitation may be unsuccessful. Planning rehabilitation Planning rehabilitation A more holistic approach to river rehabilitation is evolving. This includes specialist inputs from relevant groups including government agencies, local municipalities, river rehabilitation agencies, financial institutions, civil and hydraulic engineers, freshwater ecologists, palaeo-ecologists, historical geographers, fluvial geomorphologists, water and navigational agencies, operation companies, the general public, riparian landowners, and educational and research institutes. Adopting a holistic approach to rehabilitation adheres to the concept of Integrated Catchment Management, whereby the whole catchment is considered and not just the reach to be rehabilitated. Successful rehabilitation projects follow nine main steps. These are: developing goals and measurable objectives; river condition analysis; prioritization and project constraints; strategies; study design, techniques and rehabilitation alternatives; feasibility studies; implementation; monitoring and maintenance; and post- project evaluation. Assessing river condition Assessing river condition is an essential step in rehabilitation projects. The most useful assessments are those that compare the existing measured condition of the river to its natural condition, or to its prior state if that is less than natural, in order to measure how degraded or close to natural the system is. This prior, or reference, condition can be used to inform debate about the desired condition of the river and eventually to set the rehabilitation goals. Rehabilitation Implementation – methods and materials Successful rehabilitation efforts are based on three main activities or measures. These are environmentally sensitive river maintenance activities, soil bioengineering or soft biotechnical engineering practices and measures to mitigate the effects of hard engineering practices. Natural recovery of the river channel, without intervention, is an option where time and space allow and where other limitations, such as excessive water abstraction, are not present. Rehabilitation of banks, riparian zones and floodplains A range of off-channel rehabilitation activities can be part of rehabilitation, such as reconnection of floodplains to rivers, re-instatement of meanders, stabilisation of stream banks, and rehabilitation of riparian zones. Riparian zones can be introduced as buffer strips offering protection from catchment activities, and artificial wetlands can aid management of water quality. Five methods of stabilising stream banks are: 1) vegetation alone; 2) vegetation with structural control; 3) vegetation and structural control with bank shaping; 4) structural control alone and 5) bioengineering methods. iii Executive Summary Interventions in