DHI (Slovakia)

The common crane (Grus grus), like other soaring species of birds, uses a migration strategy to minimise the risk of wind drift over open sea, resulting in aggregation of birds along migratory corridors. With the planned large-scale development of off

PIANC EnviCom Working Group 227 is developing a decision-making guide associated with the application of environmental windows for dredging and marine navigation infrastructure construction. Dredging and construction works are often restricted during certain periods to reduce potential impacts on environmental receptors. Times when the potential environmental impacts of the project are thought or perceived to be unacceptable—and, consequently, works are not allowed—are commonly defined as seasonal restrictions. Conversely, environmental windows are the periods when works are allowed. Limiting projects to fixed environmental windows complicates contracting schedules by constricting them, adds challenges with respect to the availability of construction equipment, and extends project timelines. These limitations can also impact the safety of works and inflate their cost. The objective of this guide is to provide a risk-based decision-making process that can be applied in cases where restrictions on dredging and navigation infrastructure work may be considered. Case studies are included.

Forecasting flood and drought events requires accurate modeling tools. Hydraulic river models are based on estimates of riverbed geometry which are traditionally collected in-situ. The novel Ice, Cloud and Land Elevation Satellite 2 [ICESat-2] lidar altimetry mission with 6 simultaneous high-resolution laser beams provides the opportunity to define river cross-section geometries as well as observe water surface elevation [WSE] and water surface slope spatially resolved along the river chainage. This paper describes a method to utilize terrain altimetry and water surface slope estimates to define complete river geometries from ICESat-2 data products, using the diffusive wave approximation to calculate depth in the submerged section not penetrated by the lidar. Exemplifying the method, cross-sections are defined for a stretch of the Mekong River. Hydrodynamic model results of the stretch are compared with ICESat-2 WSE estimates and in-situ gauging station time series. Insights in river characteristics from satellite imagery and the ICESat-2 slope estimates allow for fine-tuning of the cross-sections using spatially varying Manning numbers. The final model achieves a root mean square error against the ICESat-2 WSE of 0.676 m and average Kling-Gupta Efficiency against gauging station time series of 0.880. The method is limited by the diffusive wave approximation resulting in inaccurate cross-section estimates in sections with supercritical flow or significant acceleration. Errors can be identified from ICESat-2 WSE estimates and reduced with additional cross-sections. Combined with hydrological models, the method will allow for cross-section definition without in-situ data.

Potential interchange between north Atlantic and north Pacific fish communities is modelled for future Arctic conditions under climate change. Throughout much of the Quaternary Period, inhospitable environmental conditions above the Arctic Circle have been a formidable barrier separating most marine organisms in the North Atlantic from those in the North Pacific1,2. Rapid warming has begun to lift this barrier3, potentially facilitating the interchange of marine biota between the two seas4. Here, we forecast the potential northward progression of 515 fish species following climate change, and report the rate of potential species interchange between the Atlantic and the Pacific via the Northwest Passage and the Northeast Passage. For this, we projected niche-based models under climate change scenarios and simulated the spread of species through the passages when climatic conditions became suitable. Results reveal a complex range of responses during this century, and accelerated interchange after 2050. By 2100 up to 41 species could enter the Pacific and 44 species could enter the Atlantic, via one or both passages. Consistent with historical and recent biodiversity interchanges5,6, this exchange of fish species may trigger changes for biodiversity and food webs in the North Atlantic and North Pacific, with ecological and economic consequences to ecosystems that at present contribute 39% to global marine fish landings.