Instream flow assessments for regulated rivers in South Africa using the Building Block Methodology

Abstract

The demand for water from South Africa’s growing population is creating an ever-increasing pressure on the country’s rivers. The urgent need to provide more water services often conflicts with the desire to maintain or improve the ecological condition of the rivers. To provide guidance on the sustainable use of a river’s water-resources, the Building Block Methodology (BBM) has been developed for assessing the instream flow requirement for any river. Development has been done jointly over the last five years by the national Department of Water Affairs and Forestry (DWAF) and river scientists, and the accent is on identifying a complex of different magnitude flows for maintenance of entire river ecosystems. The BBM caters for the almost universal reality in South Africa of having rapidly to provide scientific guidance on such flows for a river in cases where biological data and understanding of the functioning of the river are limited. However, the methodology works equally well in data-rich situations. The BBM depends on available knowledge and expert opinion, gleaned from experienced river scientists in a structured workshop process. Limited new data of a specific nature are gathered to facilitate the process. Relevant data on the river are prepared in a way that workshop participants can easily understand and quickly begin to use. Scientists typically involved in the workshop, all with specific roles, are those with specialist knowledge of the river or similar rivers in terms of the fish, aquatic invertebrates, riparian vegetation, river importance, habitat integrity, fluvial geomorphology, local hydraulics, water chemistry and social dependence on the riverine ecosystem. Hydrological and hydraulic modelers provide data inputs and facilitate the workshop process by answering questions and producing additional data as requested. The workshop output, reached by consensus, is a quantitative description in space and time of a flow regime that should facilitate maintenance of the river ecosystem in some pre-determined desired future state. Information from a BBM workshop is used by DWAF in the Planning phase of a proposed water-resource development. Further development of the BBM, to extend it into the Design, Construction and Operation phases, has been initiated. This includes linking with a public participation process, input into design of the scheme, base-line studies of the river and subsequent monitoring to assess the efficacy of the recommended flow regime.

Accounting for environmental flow requirements in global water assessments

“…For example, the building block model is a well-documented method for estimating EFRs at either the local or basin scale (King and Louw, 1998;King and Brown, 2010;Tharme, 2003;Hugues and Rood, 2003). The building block method supports the principle that maintaining certain components of the natural flow is of fundamental importance.…”

“…Building block method (BBM), ELOHA, DRIFT Hughes (2001), King and Louw (1998), Arthington et al (2006), Poff et al (2009), and Bunn and Arthington (2002) 2 Review of environmental flow methods…”

Ecologically Sustainable Water Management: Managing River Flows for Ecological Integrity

“…However, there is some degree and types of alteration that will not jeopardize the viability of native species and the ability of an ecosystem to provide valuable products and services for society. Around the world, river scientists are seeking better understanding of the ways and degrees to which river flows can be modified for human purposes while maintaining an adequate semblance of the composition, structure, and function of natural ecosystems (Poff et al 1997, Richter et al 1997b, Arthington and Zalucki 1998, King and Louw 1998.…”

Estimating environmental flow requirements downstream of the Chara Chara weir on the Blue Nile River

“…The comprehensive methods are based on detailed multi-disciplinary studies that often involve expert discussions and collection of large amounts of geo-morphological and ecological data (e.g. King and Louw, 1998). Typically they take many months, sometimes years, to complete.…”