A Fractal Description of Fluvial Networks in Chile: a Geography not as Crazy as Thought

Chilean geography is highly variable, not only from a climatic and hydrological point of view, but also a morphological one, showing unpredictable natural patterns with marked contrasts throughout the country, for which sometimes it is considered as a "crazy" geography. In this paper we have investigated this apparent disorganized character by exploring the fractal properties of fluvial networks extracted from basins distributed across the continental territory. Analytical and semi-empirical methods were applied, finding striking patterns of organization in the distributions of Horton parameters and the fractal dimension of the drainage networks. Fractal dimension reveals to be quite dependent on the drainage area of each unit, showing clear groupings by tectonic and climatological factors. Such dimension reveals to be an important geomorphic parameter, if not the only one able to capture the real morphology of a fluvial network. From our results and despite the diversity of landforms, hydrological, climatic and tectonic conditions, Chilean’s geography is perhaps not as crazy and disorganized as believed.

Impact of anthropogenic activity on the chemical regime of underground waters

The article is dedicated to definition of the tendency to change and pattern of formation of the chemical regime of underground waters in the Turyanchay-Girdimanchay interfluve in the Shirvan steppe, Azerbaijan as a result of anthropogenic activity. The subsoil waters studied are spread in the zone between the Turyanchay and Girdimanchay rivers. From 1930 to 2019 based on analysis of the observation of the chemical regime of subsoil waters, the natural regime of the groundwaters in the studied area strongly changed as a result of irrigation and construction works. In 1930 the average mineralization degree of subsoil waters was 26.8 gram/liter in the zone. The level of subsoil waters approaches the surface and is exposed to strong evaporation as a result of irrigation and filtration of waters from irrigation channels. Consequently, the mineralization rate of subsoil waters increased and mass secondary salinization process occurred in the irrigated lands. The average mineralization degree of subsoil waters was 33.6–34.5 gram/liter in the research zone in the 1960s-1970s. Collector-drainage networks were built and basic washing of soils is carried out in order the prevent secondary salinization and regulate the level of subsoil waters. After the 1970s the mineralization rate of subsoil waters began to decrease due to basic washing, intensive irrigation and the activity of the collector-drainage network.The average mineralization degree decreased to 15.1 gram/liter. The mineralization degree of the water in the Main Shirvan Collector which takes subsoil waters formed in the zone with 253,000 hectares and which discaharges them into the Caspian Sea decreased more than 3 times in comparison with 1995. At present the mineralization degree of collector water is 1.8–2.5 gram/liter while its mineralization degree was 8.81 gram/liter in 1995. Formation of the process in a favourable direction enchances the potential of using collector water for irrigation, technical and other purposes and creates a basis for elimination of water deficiency in drought years. The research shows that anthropogenic activity mainly plays an important role in formation of the chemical regime of subsoil waters.

Recommended dependence for hydraulic calculation of gravity drainage networks in order to improve the ecological well-being of cities

In the submitted article comparison of two calculated dependences - formulas of A. Chézyand and N.F. Fedorov used for the hydraulic calculation of gravity drainage networksare presented. For a specific example, dependence is revealed - the A. Chézy formula, which gives the highest accuracy when calculating the hydraulic slope of a gravity pipeline. The appearance of the A. Chézy formula has been clarified due to the introduction of the concept of the reduced inner diameter of the pipes. The graph of the dependence i=f (dred) is plotted, indicating that the refined form of the A. Chézy formula is more accurate. It is recommended to use the A. Chézy formula in a refined form for the hydraulic calculation of gravity drainage networks. It is proposed to develop calculation tables for the hydraulic calculation of drainage networks with internal deposits. The analysis of the calculated dependencies for the hydraulic calculation of gravity drainage networks with internal deposits presented in the paper allows recommending for practical use the formula of A. Chézy refined by the authors, according to which the authors propose to develop the Reference manual “Tables for the hydraulic calculation of gravity drainage networks with internal deposits”.

Retaining Relative Height Information: An Enhanced Technique for Depression Treatment in Digital Elevation Models

This study presents an enhanced variant of the priority-flood based algorithm proposed by Wang and Liu for treating depressions in digital elevation models (DEMs). The enhanced variant redefines spill elevation, the key concept of the original algorithm, as the lowest elevation that a pixel needs to have to ensure a non-ascending path toward the border of the DEM, plus the larger of a small number (~0.001) and the difference between the unaltered elevation values of the focal pixel and its immediate downhill neighbor. This redefinition is adopted to obtain an intermediate elevation surface to direct flow and ultimately to carve the original DEM. Each carving starts from a depression bottom and propagates downstream until a downhill cell is guaranteed in the original DEM. Tests of these algorithms on a complex terrain of the 260,000 km2 Sichuan structural basin in China shows that the enhanced algorithm maximally preserves the original flow directions and extracts realistic drainage networks. Retaining the relative heights, and therefore flow directions, of cells within depressions allows the new algorithm to offer a depressionless DEM with small modification of its origin for further hydrologic applications. The enhanced depression treatment algorithm is provided as the freely available tool BNUSinkRemv.

Water table variations on different land use units in a drained tropical peatland island of Indonesia

Restoration and water table control on peatlands to limit fire risk are national priorities in Indonesia. The present study was initiated at Padang Island, Sumatra, to increase understanding on peatland hydrology in the tropic. At the pilot site, water table and precipitation were monitored at different stations. The results show variation in water table depths (WTDs) over time and space due to spatial and temporal variability in rain intensity and drainage networks. In part of the island, large-scale drainage for plantations led to deep WTD (−1.8 m) and high WTD recession rates (up to 3.5 cm/day). Around villages, farm-scale drainages had a smaller impact with a lower recession rate (up to 1.8 cm/day) and shallow WTD, typically below −0.4 m, the threshold for sustainable peatland management in Indonesia. The recession rates levelled off at 1.0 cm/day near the drained forest/plantation and at 0.5 cm/day near the farm. Deeper layers had much lower specific yield (Sy), 0.1 at −1.5 m depth, compared with top peat soils with Sy up to 0.3. Proximity to drainages extended discharge flow to deeper layers. The results highlighted the severity of peatland drainage impact on most coastal zones of Padang Island, which have intensive drainage networks.

An experimental study of drainage network development by surface and subsurface flow in low-gradient landscapes

How do channel networks develop in low-gradient, poorly-drained landscapes? Rivers form elaborate drainage networks with morphologies that express the unique environments in which they developed, yet we lack an understanding of what drives channel development in low-gradient landscapes like those left behind in the wake of continental glaciation. To better understand what controls the erosional processes allowing channel growth and integration of non-contributing areas (NCA) over time, we conducted a series of experiments in a small-scale drainage basin. By varying substrate and precipitation, we could vary the partitioning of flow between the surface and subsurface, impacting erosional processes. Channels developed by overland flow and seepage erosion to varying extents depending on substrate composition, rainfall rate, and drainage basin relief. Seepage-driven erosion was favored in substrates with higher infiltration rates, while overland flow was more dominant in experiments with high precipitation rates. Overland flow channels formed at the onset of experiments and expanded over a majority of the basin area, forming broad dendritic networks. Large surface water contributing areas supported numerous first-order channels, allowing for more rapid integration of NCA than through seepage erosion. When overland flow was the dominant process, channels integrated NCA at a similar, consistent rate under all experimental conditions. Seepage erosion began later in experiments after channels had incised enough for exfiltrating subsurface flow to initiate mass wasting of headwalls. Periodic mass wasting of channel heads caused them to assume an amphitheater-shaped morphology. Seepage allowed for channel heads to expand with smaller surface water contributing areas than overland flow channels, allowing for network expansion to continue even with low CA. Seepage-driven channel heads integrated NCA more slowly than channel heads dominated by overland flow, but average erosion rates in channels extending through seepage erosion were higher. The experimental results provide insight into drainage networks that formed in glacial sediment throughout areas affected by continental glaciation, and highlight the importance of subsurface hydrologic connections in integrating and expanding drainage networks over time in these landscapes.

River Flood Modelling For Flooding Risk Mitigation in Iraq

River flood events have recently been increased due to many reasons such as climate change and excessive land usage. Thus, one of the greatest challenges is to control the flooding in urban areas. River flooding has become a phenomenon worldwide in general and in Iraq specifically. This is associated with the rapid increase of urbanization as well as mismanagement of land utilization; especially those located near the river banks, in addition to lack of consideration in terms of the design and implementation of drainage networks. In Iraq and especially in Al-Anbar governorate, studies in the field of flood simulation control have been rare. This study aims to suggest a fast and accurate methodology for local authorities, by providing a proposed solution and prediction of flooding area in the case study of the Fallujah barrage. Global Mapper software has been used to produce simulation photos on flooding area. Earth Explorer USGS website has been used to download water body data; and Global Digital Surface website has been used to extract and download the surface elevation data. The result of the simulation photos has predicted valuable information about the flooding area and proposed a general vision on the areas that are under threat of flooding. Four main areas were exposed to flooding, area 1, area 2, area 3, and area 4; A total flooding area of 11.89 km2. The total maximum operational level for the barrage was designed to be 44.79 m above sea level. Also, the recommended maximum operation level for the barrage was 43 m ASL. Doi: 10.28991/cej-2021-03091754 Full Text: PDF

Propagating uplift controls on high-elevation, low-relief landscape formation in the southeast Tibetan Plateau

High-elevation, low-relief surfaces are widespread in many mountain belts. However, the origin of these surfaces has long been debated. In particular, the southeast Tibetan Plateau has extensive low-relief surfaces perched above deep valleys and in the headwaters of three of the world’s largest rivers (Salween, Mekong, and Yangtze Rivers). Various geologic data and geodynamic models show that many mountain belts grow first to a certain height and then laterally in an outward propagation sequence. By translating this information into a kinematic propagating uplift function in a landscape evolution model, we propose that the high-elevation, low-relief surfaces in the southeast Tibetan Plateau are simply a consequence of mountain growth and do not require a special process to form. The propagating uplift forms an elongated river network geometry with broad high-elevation, low-relief headwaters and interfluves that persist for tens of millions of years, consistent with the observed geochronology. We suggest that the low-relief interfluves can be long-lived because they lack the drainage networks necessary to keep pace with the rapid incision of the large main-stem rivers. The propagating uplift also produces spatial and temporal exhumation patterns and river profile morphologies that match observations. Our modeling therefore reconciles geomorphic observations with geodynamic models of uplift of the southeast Tibetan Plateau, and it provides a simple mechanism to explain the low-relief surfaces observed in several mountain belts on Earth.