Introducing a new method to determine rivers’ ecological water requirement in comparison with hydrological and hydraulic methods|
Shokoohi, A. & Amini, M.
The absence of a rational, comprehensive,
flexible and easy to use method with minimum data
requirement to determine rivers’ environmental flow
requirements is the main motivation for this research.
Based on the microhabitat preferences of index species,
hydrological (the Tennant and Q95) and hydraulic methods
for determining the environmental flow requirement (EFR)
are compared. Using an ad hoc procedure, the important
species of a river at the southern part of the Caspian Sea in
Iran were distinguished, and the discharges to maintain the
microhabitat (depth and velocity) in critical months were
calculated. The observed differences between the index
species’ required velocity and depth and those suggested
by the Tennant method emphasize the importance of the
rivers morphological properties for this method application.
Allocating EFR by the Tennant and Q95 methods
would degrade the aquatic life. The EFR determined by the
hydraulic method is equal to 95 % of the average annual
discharge, which could maintain the ecological habitat in
good situation, but may provoke a conflict in the region.
The Tennant, Q95 and hydraulic methods allocate EFR as
14, 36 and 79 % of the annual flow volume, respectively.
Developing a new combined method based on using the
hydraulic method’s discharge for critical months and the
Tennant method suggestion for the excellent condition in
other months allocates 50 % of the average annual discharge.
This new method is a compromise between protecting
environment and considering the water rights of
rivers’ flow consumers and is suggested specially for dry
regions of the world.
Environmental index; Index species; Environmental discharge; Tennant; Q95; Hydraulic method; Combined method