Determination of environmental flows in rivers using an integrated hydrological-hydrodynamic-habitat modelling approach

Abstract

We propose the novel integrated modelling procedure 3H-EMC for the determination of the environmental flow in rivers and streams; 3H-EMC combines Hydrological, Hydrodynamic and Habitat modelling with the use of the Environmental Management Classes (EMCs) that are defined by the Global Environmental Flow Calculator. We apply 3H-EMC in the Sperchios River in Central Greece, in which water abstractions for irrigation cause significant environmental impacts. Calculations of the hydrodynamic-habitat model, in which the large and the small chub are the main fish species, suggest discharge values that range from 1.0 m/s to 4.0 m/s. However, hydrological modelling indicates that it is practically difficult to achieve discharges that are higher than approximately 1.0-1.5 m/s. Furthermore, legislation suggests significantly lower values (0.4-0.5 m/s) that are unacceptable from the ecological point of view. This behaviour shows that a non-integrated approach, which is based only on hydrodynamic-habitat modelling does not necessarily result in realistic environmental flows, and thus an integrated approach is required. We propose the value of 1.0 m/s as the "optimum" environmental flow for Sperchios River, because (a) it satisfies the habitat requirements, as expressed by the values of weighted useable area that are equal to 2180 and 1964 m for the large and small chub, respectively, and correspond to 82 and 95% of their respective maximum values, (b) it is consistent with the requirements of Environmental Classes A and B, whose percentiles are higher than 75% for discharge (77.2%) and for habitat availability (>83.5% for the large chub and >85.0% for the small chub), (c) it is practically achievable from the hydrological point of view, and (d) it is higher than the value proposed by the Greek legislation. The proposed modelling approach can be applied to any river or stream using the same or similar modelling tools, which should be linked via suitable coupling algorithms.

Comparing environmental flow scenarios from hydrological methods, legislation guidelines, and hydrodynamic habitat models downstream of the Marathon Dam (Attica, Greece)

“…Nearly all hydrological methods applied, including the most popular Tennant method (Tennant, ), calculated lower eflows than the ones required to ensure ecosystem integrity and functionality according to the HHM‐based, ecosystem‐oriented approach followed in our study. Previous comparative studies in various reaches (Nikghalb et al, ; Shokoohi & Amini, ; Stamou et al, ; Theodoropoulos, Vourka, et al, ) showed similar trends (but see Papadaki et al, ); Nikghalb et al () used the habitat preferences of Luciobarbus capito and calculated threefold increased eflows in comparison with those calculated using the Tennant method. Stamou et al () used the habitat preferences of Squalius peloponnensis and calculated eflows two times higher than the hydrology‐based eflows and 10 times higher than those required by the Greek legislation on eflows.…”

“…Previous comparative studies in various reaches (Nikghalb et al, ; Shokoohi & Amini, ; Stamou et al, ; Theodoropoulos, Vourka, et al, ) showed similar trends (but see Papadaki et al, ); Nikghalb et al () used the habitat preferences of Luciobarbus capito and calculated threefold increased eflows in comparison with those calculated using the Tennant method. Stamou et al () used the habitat preferences of Squalius peloponnensis and calculated eflows two times higher than the hydrology‐based eflows and 10 times higher than those required by the Greek legislation on eflows. Theodoropoulos, Vourka, et al () used benthic macroinvertebrates and calculated eflows three times higher, compared with those required by the Greek legislation.…”

“…31 of the Water Framework Directive 2000/60/EC (WFD CIS Guidance Document No. 31, ), and as Stamou et al () conclude, integrated methods could result in more “realistic” eflow values based on the historical hydrological conditions of the study area and considering what can be “socially” delivered. This conclusion however should not be misconceived as “downgrading the ecosystem‐based eflows to maximize possible short‐term human benefits in the upstream” (Homa et al, ; Jager & Smith, ).…”

“…31, ) supporting the Water Framework Directive 2000/60/EC (European Union Council, ), suggested a three‐tiered hierarchy of the eflow methods' application, depending on the detail/accuracy of the eflow prediction required and on the magnitude of the (possible) hydrological alteration due to the upstream water use (e.g., small‐scale water abstraction or the presence of a large water supply dam). However, eflows have often been calculated using only hydrological methods (e.g., Chen & Weisbrod, ; Efstratiadis, Tegos, Varveris, & Koutsoyiannis, ; Fuladipanah & Jorabloo, ; Ye, Shen, & Chen, ), whereas studies implementing and comparing eflow scenarios based on a combination of different methods in the same study area are limited (Davis & Hirji, ; Li, Cai, Fu, & Liu, ; Nikghalb, Shokoohi, Singh, & Yu, ; Papadaki et al, ; Shokoohi & Amini, ; Stamou et al, ; Tare et al, ).…”

Application of a Hydrodynamic and Water Quality Model for Inland Surface Water Systems

“…Therefore, mathematical modeling coupled with observations for verification and calibration is essential in such cases. Hydrodynamic and water quality models have been widely developed and used for the investigations of rivers [1][2][3][4], lakes or reservoirs [5][6][7][8][9][10][11], estuaries [12,13], and coastal waters [14,15] on various aspects. These models have been effective tools for explaining, simulating, and forecasting the complex processes in water environment.…”