Himalayan rivers in Nepal flow through the mountains with high gradient to emerge in lowlands as large rivers carrying enormous amount of discharge and sediments. They release significant quantity of sediment forming alluvial fan as a result of sudden decrease in gradient when they enter the lowland and gain braided form. This braided form has made the river morphologically more dynamic in nature. Division of channels into numerous anabranches leads to formation of temporary or permanent islands in between them. These islands in long run are either eroded gradually by the river channel or develop into vegetated islands. The development of vegetation may be long term with growth of trees or they may develop into grasslands that may be seasonal which is usually inundated during floods. The river channels and islands along with the surrounding floodplain with vegetation act as perfect recipe for the development of complex wetland ecosystem.

Koshi River in Nepal is among such rivers emerging from the mountains to flat plains of Terai thereby flowing into multiple channels within a large width of about 5 km, which is then controlled by Koshi Barrage at 41 km from the gorge. This dynamic river system feeds the Koshi Tappu Wildlife Reserve, a Ramsar site in the reach. The change in river course and vegetation of this large area which otherwise would be challenging to study can be done rather easily by the use of satellite imageries and cloud computing. Google Earth Engine (GEE) has been used in this study for analysing the morphological changes of the river as well as vegetation changes within the study area using the multiple satellite images taken at different times. NDWI has been calculated and used to identify the occurrence of water in the river channels, thus the morphological changes. While NDVI is used for intensity of vegetation. The temporal and spatial analysis of the morphodynamics and corresponding changes in vegetation is performed from 1987 to 2020 within the selected area.

The preliminary assessment of the results shows that the vegetation dynamics of the area has been affected by the continuous erosion and deposition caused by the morphological changes apparently due to the barrage. Over time, river has been channelizing and branching several times causing the existing islands to erode along with their vegetation as well as forming new islands with vegetation cover. This shifting of the river and resulting vegetation dynamics appear to have affected the habitat of the wild water buffaloes (Arna) as well as, other endangered species native to the area. Additional analysis on the effect of river morphology and vegetation dynamics to the flood pattern and other ecological components will be carried out to support the initial findings and draw generalized conclusions. ... Read more

Groynes have been replaced by longitudinal training walls in an 11-km long pilot project to optimize training of the river Waal in the Netherlands. These train­ ing walls improve navigability, reduce flood levels, create a sheltered second channel with more favourable ecological conditions, and decrease the erosive action on the river bed that is responsible for large-scale bed degradation. River managers wish to assess whether longitudinal training walls could have similar advantages along other parts of the Dutch Rhine branches (without excessive increase of maintenance costs). The required maintenance dredging depends on the amount of sediment entering the sheltered channel over an entrance sill situated at the upstream edge of the longitudinal training wall. Currently operational morphodynamic models cannot reliably compute this sedi­ ment flux. We present laboratory experiments to study the passage of bed sediment at different discharge distributions between the main and sheltered channel, and different degrees of submergence. ... Read more

The rapid increase in volume, resolution, and frequency of EO datasets poses the need for new scalable, cloud-based, tools for interactive exploration, visualization, and analysis. The size of data increases in several dimensions concurrently: temporal resolution go from the order of several days to several hours (CubeSats, reanalysis), spatial resolution increases from the order of hundreds of meters to order of meters (newer satellites, downscaled indicators), the spatial coverage increases from selected areas of interest to global and the timespan increases from years to decades (satellites, reanalysis).

Many datasets (optical satellite images, reanalysis of climate and coastal and ocean currents) provide a new look at the world, in details never seen before. We want to make these datasets visible, show the results, preferably without reducing dimensions and giving up all the newly achieved efforts of gathering the most detailed, most rich datasets ever created. This does leave us with a technical challenge. How can we create interactive animations of PB of geospatial data?

Here we show a new toolset and tiling scheme that helps to scale up interactive visualizations of the largest global datasets in a form of georeferenced video maps.

Interactive visualisation of sea level and currents (based on the datasets from MEASUReS, HYCOM, GTSM) provides an example of a visualisation covering several decades of sea-level rise measurements and model reanalysis. We present a way to efficiently encode data in video and reuse it in the client-side, to visualize or to perform GPU-enabled analysis. An interactive visualization of Earth’s changes captured by Sentinel and Landsat satellites and turned into video map tiles provides an example of how to disseminate large volume datasets while still being able to run state of the art algorithms on the client-side to detect land-use changes, using libraries such as TensorFlow.js or directly using computational shaders. The tools build on Google Earth Engine as a source of multi-temporal EO and reanalysis data. We show how the tools are integrated into mapping libraries (Mapbox GL, Leaflet). The storage format is based on a standardized layout of tiles (TMS). The client-side and client synchronization of video tiles are based on the emerging efforts of the w3c webtiming group. ... Read more

In this paper, we present flow and erosion problems in selected reaches of two large and dynamic river systems in South Asia, namely the Koshi River in Nepal (and India) and the Lower Brahmaputra (Jamuna) in Bangladesh. We attempted to analyse large- and meso-scale (short- and medium-term) morphological changes with a focus on the dynamics of deep-channels, revealing their importance for the river and riverbank erosion management. This focus on deep-channels is a key change of perspective as most morphological studies and analyses of large rivers are usually focused on sandbar and braiding dynamics. We used ground data, satellite imagery, and explorative morphological modelling to quantify and analyse the flow and morphological processes. We demonstrate how multispectral satellite imagery can be processed using Google Earth Engine to assess the spatiotemporal dynamics of morphological processes and changes. We also analysed bathymetric surveys to assess short-term changes of meso-scale morphology that are not fully captured by the satellite data analysis. The morphological modelling provided first results on reproducing essential processes, such as growth and migration of meso-scale features, particularly deep-channels, under varying flow conditions. Some features of these reaches of two rivers differ, but particularly the importance of deep-channel dynamics was revealed for both. We infer that the seasonal and annual discharge variabilities are key factors for the dynamic behaviour of bank, char (island), sandbars and deep-channels, particularly regarding short- and mid-term changes. We also infer that morphologically extreme situations do not always occur during high flows, but rather through the concentration of the flow along the deep-channels during medium and lower flows. ... Read more

One of the challenges as a researcher is to provide the context in current events. A coastal city floods, a reservoir runs dry, a new dam is created, a river finds a new path, part of a country experiences a drought. For each of these events, relevant geospatial datasets exist. Collecting, processing and visualizing these datasets requires experience, time and resources. These are often not available in the context of current events. What if we could make these EO data available to help journalism, citizen science, and researchers to quickly evaluate current events?

Here we show a new tool to create and share interactive video map stories. The tool allows to easily turn multitemporal EO or reanalysis data into a set of georeferenced and tiled videos which can be used to better communicate Earth’s changes in journalism, social media, or to support research. The tool allows concurrent generation of video map stories by multiple users via a map-based interface which can then be easily shared.

The open-source app makes use of Video Map tools (built on Google Earth Engine API) to expose multitemporal geospatial datasets as a zoomable playing video story, which can be enriched by markers, and put into the context of a storytelling layout. The story can be shared using a unique url on social media.

We find that providing video maps is an effective way to put events into context. We will present several examples of video maps. Several applications optical images (Landsat and Sentinel-2), and surface-water change detection show the context of a day zero event in South Africa. Moving populations based on the night lights of the VIIRS show challenges in the Ethiopian, Sudanese, Eritrean border after the dam was constructed. Ocean and coastal currents derived from the Global Tide and Surge Model and HYCOM reanalysis allow to reconstruct the currents and reconstruct the final days of a ship lost at sea. Video maps based on the TROPOMI mission allow to zoom in and look at the sources of atmospheric pollution (NO2).

By making these stories available at the fingertips of journalists, citizens and scientists we hope to help provide more detailed and accurate context for the many challenges that our world is currently facing. ... Read more

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper. ... Read more