Mapping Flow-Obstructing Structures on Global Rivers

To help store water, facilitate navigation, generate energy, mitigate floods, and support industrial and agricultural production, people have built and continue to build obstructions to natural flow in rivers. However, due to the long and complex history of constructing and removing such obstructions, we lack a globally consistent record of their locations and types. Here, we used a consistent method to visually locate and classify obstructions on 2.1 million km of large rivers (width ≥30 m) globally. We based our mapping on Google Earth Engine’s high resolution images, which for many places have meter-scale resolution. The resulting Global River Obstruction Database (GROD) consists of 30,549 unique obstructions, covering six different obstruction types: dam, lock, low head dam, channel dam, and two types of partial dams. By classifying a subset of the obstructions multiple times, we are able to show high classification consistency (87% mean balanced accuracy) for the three types of obstructions that fully intersect rivers: dams, low head dams, and locks. The classification of the three types of partial obstructions are somewhat less consistent (61% mean balanced accuracy). Overall, by comparing GROD to similar datasets, we estimate GROD likely captured >90% of the obstructions on large rivers. We anticipate that GROD will be of wide interest to the hydrological modeling, aquatic ecology, geomorphology, and water resource management communities

A Picture of the Research Field of Doctoral Education from the Students’ Perspectives : Studies Using Questionnaires and Scales

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Thermal conductivity of Ice prepared under different conditions

Although the thermal conductivity of liquid water is well established, many conflicting values for the thermal conductivity of ice have been reported in the literature. This work demonstrates that the significant differences in the reported ice thermal conductivities can be attributed to differences in the freezing conditions and measurement procedures. In this study, the thermal conductivity of ice was measured over the temperature range of -5 to -40 °C using a commercial needle probe. The heating time and data fitting method were first optimized. Then, the effects of the freezing rate, presence of dissolved gasses in the water and presence of a magnetic field during freezing on the thermal conductivity of ice were determined.This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) through project AGL2012-39756-C02-01. A.C. Rodríguez acknowledges a predoctoral contract from MINECO through the National Program for the Promotion of Talent and its Employability (National Sub-Program for Doctors Training).Peer reviewe