Hydrological regime assessment

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Hydrological regime assessment


Hydromorphological assessment methods

Brief description

Methods for the assessment of hydrological regime alteration analyze specific hydrological indicators of rivers and streams to assess the impact of human pressures on the hydrological regime. They often focus on alterations which affect the longitudinal continuity of water flow (e.g. intakes, impoundment, diversions) and mainly focus on the reach scale. Methods widely use models to obtain data from ungauged reaches or incomplete data series. We reviewed 10 methods in total (4 for European countries and 6 for non-European countries) (Table 1).

Strengths, limitations and gaps

Methods for the assessment of hydrological regime alteration make use of indicators derived by quantitative, statistical or physically-based models. This implies the use of existing large data sets and long-time series, which represent the main limitation. Moreover these methods often do not take into account small scale hydrological alterations (e.g. hydropeaking) as well as groundwater/surface interactions, important for organisms.

Other relevant information

Summary tables of analyzed assessment methods for hydrological regime are available here:

- For European countries: File:4 EU.pdf

- For non European countries: File:4 nonEU.pdf

In the table we recorded whether the analyzed method considers or not a specific feature. Three options were considered: presence (tick), absence ( ), and probably assessed (PA), the latter indicating when there is an uncertainty concerning whether the feature is collected and/or when the feature may be indirectly obtained.

Table 1 lists the key and the analyzed references for methods of hydrological regime assessment.

Table 1. Analyzed references for methods of hydrological regime assessment.

A special focus on Environmental Flows

The Eflows concept is close to the environmental objectives of the WFD directive, which require that the flow regime should provide conditions “consistent with the achievement of the values specified for the Biological Quality Elements”. An extensive analysis and review of the Environmental flows (“Eflows”) methods is not included in our analysis of the existing methods for the assessment of hydrological regime alteration, although they usually start from a basic evaluation of the modifications in flow regime from near-natural conditions. This is because the specific aim of environmental flow methods is to assess flow requirements of the many interacting components of aquatic systems (Arthington, 1998; King et al., 2008), and the output is a description of a flow regime needed to achieve and maintain a specified river condition. It has been estimated that some 200 different generic methods have been developed to derive ‘environmental flows’ (Tharme, 2003; Arthington et al., 2006). The differences among the various methods depend on the purposes of application, the specific characteristics of the case study, and the type of issue to be addressed (water planning, monitoring, river restoration plan, etc.). A comprehensive review of this category of approaches and methods is reported in Arthington (1998), King et al. (2008), and Navarro & Schmidt (2012).

In the context of the WFD, some countries developed specific environmental flow indicators which are then employed for the objectives of the WFD as well. This is, for example, the case of UK, where the Environmental Agency developed the EFI (Environmental Flow Indicator; http://www.environment-agency.gov.uk/business/topics/water/119927.aspx). The EFI is used both to prioritize water resources management (i.e. water abstraction), but also to make a “compliance assessment” to state whether a river may or may not reach the good ecological state as required by the WFD. The potential of those methods and indicators is high and they have been recently largely diffused in the European context. However their use may become more complex and difficult in those regions where the flow regime is highly variable and lowly predictable. This is the case of Mediterranean rivers, where the assessment of the alteration of the natural regime should require a wider set of indicators.


Arthington A.H. (1998): Comparative Evaluation of Environmental Flow Assessment Techniques: Review of Holistic Methodologies. LWRRDC Occasional Paper 26/98. ISBN 0 642 26745 6.

Arthington A.H., Bunn S.E., Poff N.L., Naiman R.J. (2006): The challenge of providing environmental environmental flow rules to sustain river ecosystems. Ecological Applications 16:1311-1318.

Black A.R., Bragg O.M., Duck R.W. and Rowan J.S. (2005): DHRAM: a method for classifying river flow regime alterations for the EC Water Framework Directive. Aquatic Conservervation: Marine and Freshwater Ecosystems 15:427–446.

Henriksen J.A., Heasley J., Kennen J.G. and Niewsand S. (2006): Users’ manual for the Hydroecological Integrity Assessment Process. U.S. Geological Survey, Biological Resources Discipline, Open File Report 2006-1093, 80 p.

(ISPRA) Istituto Superiore per la Protezione e la Ricerca Ambientale (2011): Implementazione della Direttiva 2000/60/CE. Analisi e valutazione degli aspetti idromorfologici. Versione 1.1. Istituto Superiore per la Protezione e la Ricerca Ambientale, Roma, 85 p.

King J.M., Tharme R.E. and de Villiers M.S. (eds) (2008): Environmental flow assessments for rivers: manual for the Building Block Methodology. WRC Report No TT 354/08. Updated Edition. Water Research Commission, Pretoria, South Africa.

Kleynhans C.J., Louw M.D., Thirion C., Rossouw N.J. and Rowntree K. M. (2005): River EcoClassification: Manual for EcoStatus determination (Version 1), Joint Water Research Commission and Department of Water Affairs and Forestry (South Africa). Report No. KV 168/05, 210 p.

Martínez Santa-María C. and Fernández Yuste J.A. (2010): IAHRIS 2.2. Indicators of Hydrologic Alteration in Rivers. User’s Manual. Ministry of the Environment - Polytechnic University of Madrid – CEDEX, 66 p. http://www.ecogesfor.org/IAHRIS_es.html

Munné A., Solà C. and Pagés J. (2006): HIDRI: Protocolo para la valoración de la calidad hidromorfológica de los ríos. Barcelona, Agència Catalana de l’Aigua, 164 p.

Navarro R.S. and Schmidt G. (2012): Environmental Flows in the EU. Discussion Paper. Version Draft 1.0, for discussion at the EG WS&D, 23 April 2012, 45 p.

(OWEB) Oregon Watershed Enhancement Board (2000): Oregon Watershed Assessment Manual, 583 p.

Richter B.D., Baumgartner J.V., Powell J. and Braun D.P. (1996): A method for assessing hydrologic alteration within ecosystems. Conservation Biology 10(4):1163-1174.

Richter B.D., Baumgartner J.V., Braun D.P. and Powell J. (1998): A spatial assessment of hydrologic alteration within a river network. Regulated Rivers-Research & Management 14(4):329-340.

Shiau J.-T. and F.-C. Wu (2008): A Histogram Matching Approach for assessment of flow regime alteration: application to environmental flow optimization. River Research and Applications 24(7):914-928.

Tharme R. (2003): A global perspective on environmental flow assessment: emerging trends in the development and application of environmental flow methodologies for rivers. River Research and Applications 19:397-441.

The Nature Conservancy (2009): Indicators of Hydrologic Alteration Version 7.1. User's Manual, 81 p.