Flows and Transport in Rivers - Hydro-Environmental Analysis: Freshwater Environments - page 110

TABLE 4.6
7Q Flow Uses Source

7Q Flow Uses Source

7Q1 Known as the “dry weather low” Smakhtin (2001)

Used for abstraction licensing Smakhtin (2001), Smakhtin and Toulouse

(1998)

Used to remove the effect of minor river regulation Matalas (1963)

7Q2 One of the most widely used design low-low indices Smakhtin (2001), Smakhtin and Toulouse

(1998)

Habitat maintenance low (represents a period of stress on the
system that causes some reduction in populations)

Ontario Ministry of Natural Resources
(1994)

Criteria for developing permits for wasteload allocations Tortorelli (2002)

Used as an instream low Caissie and El-Jabi (2003)

Some use as a speciic design application for stormwater
holding facilities based on stormwater modeling

Odom (2004, personal communication)

Not deined Beran and Gustard (1977), Hayes (1991),

Ries and Friesz (2000)

7Q5 Critical low low for low-quality ishery waters (a stream

classiied for the beneicial use of warmwater semipermanent
ish life propagation or warmwater marginal ish life
propagation)

South Dakota Department of Environment
and Natural Resources (1998)

7Q20 Used as a system's extinction low (causes signiicant stress on

the system)

Ontario Ministry of Natural Resources
(1994)

Used as an indicator of the minimum low needed to maintain
the ecosystem

Ontario Ministry of Natural Resources
et al. (2003)

Limiting condition for sewage treatment and wastewater
disposal for a receiving waterbody

Ontario Ministry of the Environment
(2000)

Indicator of potential mortality of aquatic life for larger
streams

Imhof and Brown (2003)

Summer design low low for efluent wastewater discharge and
drought low periods and volumes

Cusimano (1992)

Flow for sustainable yield/carrying capacity for ecotourism Shrivastava (2003)

7Q25 Critical low low for high-quality ishery waters (surface

waters designated for the beneicial use of cold-water
permanent ish life propagation, cold-water marginal ish life
propagation, or warmwater permanent ish life propagation)

South Dakota Department of Environment
and Natural Resources (1998)

Source: Pyrce, R.S., Hydrological low low indices and their uses, Watershed Science Centre, Peterborough, Ontario,
2004.

4.6.2 e nVIronMentaL f LowS
While minimum lows, such as the 7Q10 low, have commonly been used, it has long been recog-
nized that maintaining some constant minimum low is not conducive to the long-term health of
aquatic communities. The sustainable management of rivers toward the long-term health of both the
ecological and economic systems of a given watershed or country is one of the most crucial issues
for current and future generations (Wali et al. 2009). A critical component of the allocation of waters
among various competing land uses/covers is in identifying a desirable state for a river ecosystem
and the low requirements for maintaining that state, typically referred to as the environmental low
or the environmental low requirement (EFR; Mazvimavi et al. 2007). Environmental lows have
been variously deined. One useful deinition is that included in the 2007 Brisbane Declaration: