Latest revision as of 11:52, 7 January 2019

Ensure minimum flows

Category 03. Flow dynamics improvement

General description

Minimum flow (i.e. a remaining minimum water level; no drying-out) in a stream is required to sustain its hydrological and ecological functions and to conserve its ecological quality (European Environemnt Agency). This needs to be considered in the management of aquatic ecosystems, especially in semi-arid regions. The provision of minimum flow becomes even more important in terms of climate change. Minimum flow can be (artificially) maintained by management methods (e.g. at reservoirs), with restrictions (e.g. abstraction constraints during summers, especially during periods of low precipitation), with changes in national water rights, and with morphological measures. The concept of minimum flows should ensure that the economic use of water can continue while enough water remains in the stream channel to maintain the ecosystem (see e.g. the Otago Regional Council information on minimum flow). At the beginning of the concept minimum flow was mainly required to ensure the dilution of pollutants and to keep rivers minimally flooded to protect individual species (most certainly fish). The concept of eflows evolved from this concept. For further information about eflows please see the respective REFORM Wiki page on EFlows.

Applicability

Semi-arid regions are most certainly endangered for water scarcity and droughts. The concept of minimum flows aims to ensure the economic use of water while enough water remains in the stream channel to maintain the aquatic ecosystem. A combination of hydrological and morphological measures can be established to ensure minimum flows: Hydrological measures ensuring the maintenance of minimum flows by (i) management methods (e.g. at reservoirs), (ii) with restrictions and regulations (e.g. controls on surface and groundwater abstractions during dry seasons) and (iii) with adaptations in national water rights. Morphological measures can increase the retention of water (i) within the stream channel, e.g. by improving aquatic habitats in order to make them less vulnerable to flow disturbances, and (ii) in the floodplain, e.g. increasing the connectivity of floodplain and stream channel (REFORM Wiki page on measures to enlarge inundation and flooding). We would also refer to Thomas et al. (2011) who reviewed mitigation measures to sustain minimum runoff considering the whole catchment. E.g. they account to changes in land use to lower evapotranspiration and to increase groundwater recharge affecting the base flow in streams.

Expected effect of measure on (including literature citations):

There was not much literature found about effect of measures on biota. However, the maintenance of minimum flows can be expected to positively affect stream biota such as fish and benthic invertebrates, e.g. species can be protected in a refugium during dry seasons. Water quality (including e.g. water temperature and higher dilution of pollutants) can also be expected to be positively affected. Thomas et al. (2011) compiled a table to assess mitigation measures during periods of low flow. They do not account for effects on biota but they summarize different variables for mitigation measures such as time to establish and effort for operation. This table can be especially helpful prior to the implementation of measures.

Temporal and spatial response

not available

Pressures that can be addressed by this measure

• Discharge diversions and returns
• Hydrological regime modification
• Impoundment

Cost-efficiency

not available

Case studies where this measure has been applied

• Westlicher Abzugsgraben
• Fish ramp Friedrichsgüte
• Fish ramp Baumannsbrücke
• Klein Wall
• Maxsee
• Renaturierung Untere Havel
• Kuivajoki - Hirvaskoski
• Mörrumsån - Hemsjö
• Heltondale Beck Flow restoration

Useful references

• Colorado Department of Natural Resources - Instream Flow Program.
• European Communities (2015). Guidance Document No. 31. Ecological flows in the implementation of the Water Framework Directive. doi: 10.2779/775712
• European Environment Agency website on minimum flows (accessed October, 4th 2015).
• REFORM Deliverable 2.2 Part 2
• Otago Regional Council - Minimum flow and integrated water management programmes
• Thomas B., Steidl J., Dietrich O. & Lischeid G. (2011): Measures to sustain seasonal minimum runoff in small catchments in the mid-latitudes: A review. Journal of Hydrology, 408, 296.307.

Other relevant information