2D vs. 3D Numerical Approaches for Fish Habitat Evaluation of a Large River — Is 2D Modeling Sufficient?

Computational Fluid Dynamics is an effective tool for assessing non-present conditions, thus also in habitat evaluation within ecohydraulics. Deciding whether to apply a one-, two- or three-dimensional numerical approach, is an optimization that needs to be performed by every task, given the capability and the demands of specific approaches. In this paper we compare the utility of two-dimensional (2D) versus three-dimensional (3D) hydrodynamical simulations for ecohydraulic purposes. The basis of the comparation were 1) three simulated abiotic variables: water depth, depth averaged flow velocity and bed material composition, and 2) an overall performance in a meso-scale fish habitat evaluation, based on the simulated three variables. The biotic parameters for the models were the habitat suitability curves of three fish species, the Danube streber (Zingel streber), the round goby (Neogobius melanostomus) and the white bream (Blicca bjoerkna). We found that in terms of ecohydraulic utilization, the 2D approach performed sufficiently to simulate the hydrodynamics of a large river. The errors originating from the 3D-2D simplification yielded negligible differences in habitat evaluation, and the agreement in the habitat suitability indices calculated from the simulated metrics was satisfactory. Henceforth, the theory was turned into an application as we performed habitat mapping on a 100 km long, Hungarian reach of the Danube River, with the abiotic parameters resulting from a 2D hydrodynamical simulation. The possibility of simplifying the approach from 3D to 2D provides a cost-efficient numerical tool at larger scales for ecohydraulic studies, and especially for evaluating habitat suitability of riverine fish.

Sediment Management: Hydropower Improvement and Habitat Evaluation

It is predicted that 60% of all new energy investments over the next 20 years will be in renewables [...]

“Adapted” Habitat Evaluation Procedure and Choice Experiment: Substitutes or Complements?

In this paper, we assess the environmental benefits derived from a wetland restoration plan. We assume that some of these benefits are “familiar” and thus fully perceived by the population; whereas those with more complex origins are “unfamiliar” and thus poorly perceived and valued. Well perceived benefits can often be assessed from carefully constructed conventional economic approaches based on preferences. However, the biases of these approaches become too significant for poorly perceived benefits which require alternative valuation methods. The “adapted” Habitat Evaluation Procedure (HEPa) “benefit” seeks to value environmental benefits through a non-monetary metric, the habitat unit. It evaluates marginal environmental changes using ecological indicators instead of preferences. Our aim is to test the possibility of combining a conventional monetary valuation method (choice experiment) with a non-monetary alternative valuation method (HEPa) to see whether such a combination could improve the assessment of benefits stemming from positive impacts of environmental policies. By so doing, we seek to contribute to a better integration of ecosystem services into the processes of planning, management, and decision-making regarding natural areas.

Environmental Regeneration for a Small-Scale Beach “Heda-Mihama Project”

In 1950’s and 1960’s, Mihama beach in Heda Bay located on western coast of Izu peninsular had been famous for the richness in shell fauna, for example, about 400 species including rare ones were collected. In 2000’s, however, the impoverishment of ecosystem function has become considerable, which led us to project the investigation on the origin and restoration. The authors carried out field survey in 2007–2008 and found that the impoverishment of Mihama is derived not from surface water but from the benthic environment. The measured water current at the site was quite small, which indicated the water exchange was very weak. It must be one of the main causes of unfavorable benthic environment. Thus environmental regeneration plans for Mihama was proposed in which the pears blocking the water current be removed. In order to assess the effect of proposed plans, simulation-based habitat evaluation was conducted. A three-dimensional hydrodynamic and sediment transport models were developed to reproduce the characteristics of currents and predict the sediment size around Mihama. For the assessment of the ecological status, HEP (Habitat Evaluation Procedure) was employed, in which one of the typical species of bivalves is chosen as a target species. Water depth, sediment size, friction velocity at the bottom, etc. were considered as the environmental factors for the target species. The suitability indices (SI) for each environmental factors were calculated by using the results of hydrodynamic and sediment transport simulations. By using the developed scheme, total habitat unit was evaluated for the proposed regeneration plans and compared to that without countermeasures. It was predicted that the removal of the piers will improve the habitat condition in the target site. Based on the proposal by the authors, a water pathway under the pier was built in 2009. The authors conducted field survey again in 2014 and confirmed that the benthic environment has been improved.

Application of Habitat Evaluation Procedure with Quantifying the Eco-Corridor in the Process of Environmental Impact Assessment

In contrast to other fields, environmental protection (e.g., habitat protection) often fails to include quantitative evaluation as part of the existing environmental impact assessment (EIA) process, and therefore the EIA is often a poor forecasting tool, which makes selecting a reasonable plan of action difficult. In this study, we used the Habitat Evaluation Procedure (HEP) to quantify the long-term effects of a road construction project on an ecosystem. The water deer (Hydropotes inermis) was selected as the species of study since it uses an optimum habitat; water deer habitat data were collected on vegetation cover, stream water density, geographic contour, land use class, and road networks. The Habitat Suitability Index (HSI) and Cumulative Habitat Unit (CHU) values for the water deer were estimated to investigate the major land cover classes, the national river systems, and vegetation cover. Results showed that the environmental impact in the road construction project area would result in a net ecological loss value of 1211 without installation of an eco-corridor, which reduced to 662 with an eco-corridor, providing a 55% increase in the net value after 50 years of the mitigation plan. Comparing the 13 proposed ecological mitigation corridors, the corridor that would result in the highest net increase (with an increase of 69.5), was corridor #4, which was regarded as the most appropriate corridor to properly connect water deer habitat. In sum, the study derived the net increase in quantitative values corresponding with different mitigation methods over time for a road construction project; this procedure can be effectively utilized in the future to select the location of ecological corridors while considering the costs of constructing them.