Flood hazard on the Upper Angara river

The article provides the results of studies on flooding in the rivers of the northern Baikal on the example of the Upper Angara river basin. Some information about the situation with floods and mudflows in the dynamics since 1933 is highlighted. Spatial and temporal patterns of maximum levels, water discharge, duration of high levels, intensity of the water rise have been studied using standard methods of processing hydrological information to assess risks and hazard. On the basis of long-term observation series, expedition surveys we considered classification geohydrological characteristics of floods by genesis of their formation, recurrence of extreme levels, intensity and depth of floodplain inundation. The areas of possible flooding and waterlogging have been determined on the basis of large-scale maps using GIS technologies using ArcGIS. Settlements and infrastructure facilities located in hazardous areas have been identified. Engineering measures to mitigate flood risks in the Upper Angara river have been proposed.

Juvenile Chinook salmon use of sandbar willows in a large-scale, simulated riparian floodplain: microhabitat and energetics

Outmigrating, juvenile Chinook salmon Oncorhynchus tshawytscha, with access to floodplains (e.g., Yolo Bypass California, USA), grow faster than those restricted to the main channel of the Sacramento River. How these young salmon might use rooted, vegetative structure (e.g., to decrease energy expenditures) while holding positions in flowing water on floodplains and flooded riparian zones is unknown. We conducted daytime experiments in a large (24.4 m long) flume containing a planted area (9.76 m × 1.22 m) of sandbar willows, Salix interior. Flume water was maintained at 1.5 m depth and 16 °C over a 15–90 cm s−1 test velocity range. Fish were videoed using 19 cameras to determine positional behavior, including their depth, use of vegetation, and tail-beat (body-undulation) frequencies (TBFs). These TBFs were replicated with similarly-sized salmon in a calibrated, Brett-type swimming respirometer, where oxygen consumption rates were measured. Using these laboratory measurements, we estimated their swimming velocities and energetic costs associated with occupying sandbar willow habitats in the flume. As flume velocities increased and the leafy canopies of the willows were bent over from the flow, salmon occupied deeper water, among the thick stems of the willows, and maintained their positions. Even at the highest (90 cm s−1) nominal flume velocities, their estimated swimming velocities were only 35.6 cm s−1, within the bottom 15 cm of the water column. This resulted in unchanged energetic costs, compared with those estimated at lower nominal water velocities. The use of vegetated (e.g., with sandbar willow common to the riparian zone) floodplains, rather than non-vegetated ones, can potentially provide energy-saving, growth-promoting daytime habitat for migrating juvenile salmonids during river-flow periods that include floodplain inundation.

Effects of Inundation on Water Chemistry and Invertebrates in Floodplain Wetlands

Floodplain wetlands play a significant role in the storage of sediment and water and support high levels of nutrient cycling that lead to substantial primary production and high biodiversity. This storage, cycling and production system is driven by intermittent inundation. In regulated rivers the link between channel flows and floodplain inundation is often impacted with reduction in the frequency and duration of inundation. Managed floodplain inundation is us being used as a tool to help restore floodplain wetland processes and rehabilitate river systems. However, the use of managed water for the environment remains contentious and it is important to quantify the outcomes of re-introducing water to floodplain wetland systems. We examined the effects of environmental floodplain watering on water chemistry and three groups of invertebrates, including benthic and pelagic invertebrates and macroinvertebrates, in wetlands on the Gwydir River system in the north of the Murray-Darling Basin. We hypothesised that wetlands that were inundated for longer periods of time would have altered water chemistry and support a greater richness and abundance of invertebrates, thus altering their assemblage structures. Water chemistry and the assemblage structure of all three invertebrate groups in the wetlands was significantly influenced by the time since connection (TSC) to their respective rivers and therefore inundation period. The microinvertebrate abundance of was positively associated with TSC, but not macroinvertebrates. This suggests that the duration of connection between the channel and floodplain is important in maintaining the ecology and food webs in the wetlands.

Marine heatwaves in the dynamics of the Pantanal´s historical drought and unprecedented fires

<p>Fire is a natural disturbance in the Neotropical savannas, and rather frequent in the relatively<br>dry and well-drained seasonal savannas of the Brazilian Cerrado. The neighboring Pantanal, on<br>the other hand, is a seasonally flooded savanna and the largest wetland in the world (≈138,000<br>km 2 ). Due to its wetter condition, fires in the Pantanal are much less frequent and spatially<br>restricted. But, given an ongoing extreme drought, the 2020’s fires in the Pantanal have been<br>unprecedented in extent and duration: About one third (≈45,000 km 2 ) of the area of this<br>important wetland has gone up in flames since last January. Regarding this historical drought,<br>climate change has been identified as one of the most important threats to the Pantanal.<br>Reductions in precipitation may cause significant disturbances in its ecological functioning,<br>affecting hydrological, floodplain inundation dynamics, as well as fire regime. Climate change<br>models from a recent study (Thielen et al. 2020, doi:10.1371/journal.pone.0227437) indicate<br>that, for the Pantanal, extended severe droughts are to be expected from the warming of Sea<br>Surface Temperatures (SST) at Northern Hemisphere oceans.<br>The present study analyses the spatial and temporal dynamics of precipitations during the<br>series 1981-2020 in the Upper Paraguay River Basin (UPRB), which comprises the Pantanal and<br>the neighboring Highlands, along with a co-evaluation of the SST trends at three oceanic<br>regions from Northern Hemisphere. Precipitation anomalies were analyzed by mean of the<br>Standardized Precipitation Drought Index (SPDI) based on the 1981-2010 climate normals.<br>Results show that for the UPRB, negative precipitation anomalies occur in pulses lasting<br>several years. A drought starting in 2019 has been the strongest and most extended on record,<br>persistently reaching the Extremely Dry condition (SPDI≤-2.0) during 2020. As early as Mar,<br>over 64% of the Pantanal is affected by such drought, and around 83% by Dec. For the UPRB,<br>four distinctive groups of subregions were identified according to their temporal dynamics of<br>mean SPDI values, mainly during Sep2019/Feb2020 and Mar2020/Dec2020. Here, precipitation<br>anomalies from southernmost subregions of the Pantanal were less intense and even not<br>affected by the drought.<br>As for SST, the Northeast Pacific region (PAC-NE) showed the most important dynamics. In this<br>region, SSTs have been anomalously warm since Jun 2019, with 64% of the time SSTA<br>surpassing the 90 th percentile: reaching the Heatwave condition. With a lead of one to two<br>months, PAC-NE showed the strongest (and negative) correlation with precipitation at UPRB<br>(r=-0.87) during Jan2019 to Dec2020. There is a significant trend for an increase in SST at the</p><p>Northeast Pacific, a trend that will certainly generate a rather continuous Heatwave in PAC-NE.<br>As a result, one expects an extension of the current extreme drought in the Pantanal area, at<br>least during 2021, and the intensification of fires with unprecedented duration and intensity,<br>extending now to areas historically flooded or perhumid. Concomitantly, we predict a most<br>definite impact on non-fire-resistant vegetation cover, as well as ecosystem functioning and<br>biodiversity.</p>

Measuring Floodplain Inundation Using Diel Amplitude of Temperature

Assessment of inundation patterns across large and remote floodplains is challenging and costly. Inexpensive loggers that record the damping of the diel amplitude of temperature (DAT) when submerged compared to overlying air can indirectly indicate inundation. We assessed the efficacy of this approach in tropical, subtropical, and temperate floodplains by comparing direct water level measurements using pressure transducers with the indirect indication of inundation ascertained from the DAT at the same location. The approach worked better in tropical than in subtropical and temperate floodplains. However, the relatively small DATs of air in humid and densely vegetated settings made estimation of inundation more challenging compared to the drier and less vegetated settings, where a large diel range of air temperature was markedly damped beneath the water. The indirect temperature approach must be calibrated for a particular ecosystem using direct water-level measurements to define DAT thresholds that are indicative of submergence of the sensors. Temperature provides an inexpensive indicator of duration of inundation that can be particularly useful in studies of large and remote floodplains, although the development of inexpensive sensors that directly measure submergence (e.g., by resistivity) will likely become a better option in the future.

Environmental Flow Releases for Wetland Biodiversity Conservation in the Amur River Basin

Flow regulation by large dams has transformed the freshwater and floodplain ecosystems of the Middle Amur River basin in Northeast Asia, and negatively impacted the biodiversity and fisheries. This study aimed to develop environmental flow recommendations for the Zeya and Bureya rivers based on past flow rate records. The recommended floodplain inundation by environmental flow releases from the Zeya reservoir are currently impracticable due to technical reasons. Therefore, the importance of preserving the free-flowing tributaries of the Zeya River increases. Future technical improvements for implementing environmental flow releases at the Zeya dam would improve dam management regulation during large floods. The recommendations developed for environmental flow releases from reservoirs on the Bureya River should help to preserve the important Ramsar wetlands which provide habitats for endangered bird species while avoiding flooding of settlements. The results emphasize the importance of considering environmental flow during the early stages of dam planning and the need to enhance the role of environmental flow in water management planning.