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Environmental Gradients, Boundaries, and Buffers: An Overview
Published in George Mulamoottil, Barry G. Warner, Edward A. McBean, Wetlands, 2017
Environmental gradients are the primary reason for consideration of buffers and boundaries — any watershed contains elevation and moisture gradients as we move from the drainage divide to the lowest elevation and from the small headwater tributaries to the larger-order mainstem. In some cases, wetlands form an ecotone between upland and deepwater habitat; in many cases, wetlands are the endpoint of ground and surface water flows, and sometimes the wetland itself is large enough to contain significant environmental gradients. Materials and energy flow along these environmental gradients across the boundaries and buffers.
The hydrologic system
Published in Stephen A. Thompson, Hydrology for Water Management, 2017
Moving down in spatial scale from the global to the level of the individual drainage basin brings additional storages and processes into view (Fig. 1.2). A drainage basin is an area of land that drains water to a common outlet. Because of this physical continuity the drainage basin scale is extremely useful in many hydrologic investigations. In the United States drainage basins are also called watersheds. The topographic line separating adjacent drainage basins is the drainage divide. At this scale we see that precipitation may be intercepted by vegetation. Intercepted water may evaporate back into the atmosphere, or it may drip or flow down plant stems to the surface. Water reaching the surface may flow across the surface as overland flow toward stream channels, it may infiltrate the soil, or it may be retained as depression storage within surface irregularities. Infiltrated water may move vertically downward eventually reaching the water table, which represents the top of the groundwater zone. Underground water may move horizontally in the unsaturated zone as interflow. Groundwater flow in the saturated (groundwater) zone may eventually reemerge as baseflow in streams. Groundwater flow may or may not coincide surface water drainage. Of course at every opportunity water will return to the atmosphere through the process of evapotranspiration.
Eugéne Belgrand (1810-1878): civil engineer, geologist and pioneer hydrologist
Published in Denis Smith, Water-Supply and Public Health Engineering, 2017
The river basin, bounded by its drainage divide and subject to surface and sub-surface drainage under gravity to the ocean or to interior lakes, forms the logical area unit for hydrological studies. Rosemary J. More, Water, Earth and Man: a synthesis of hydrology . . . (London, Methuen, 1969).
Key indicators describing the evolution of landslides in the Zhuoshui River Basin caused by the Chi-Chi earthquake in Taiwan
Published in Geomatics, Natural Hazards and Risk, 2022
Chao-Yuan Lin, Yung-Chau Chen, Jing-Yao Lin, Yu-Sen Mao, Shao-Wei Wu
The study area is the Zhuoshui River Basin, which spans Changhua County, Nantou County, Yunlin County, Chiayi County, and other areas. The catchment area is 3162 km2 and the most upstream is Wushe River, which gathers the water from the west drainage divide of Hehuan Mountain and flows down the rift valley in the southwest direction, until it converges with the several streams which flow into Zhangyun Plain afterwards. The topography of the basin varies greatly. The highest elevation is 3941 m. The main slope is the sixth grade (55–100%), and the western slope direction occupies the most area. In this study, the terrain uplift in the short and medium term (1–10 years) has no substantial significance. It can be regarded as a uniform profile for this equilibrium state. There are a total of 12 main tributaries of the Zhuoshui River. They are Tarotwan, Wanda, Liqi, Kashe, Danda, Junda, Zhuogun, Chenyoulan, Shuili, Qingshuigou, Beishi, and Qingshui Stream, respectively (Figure 1). In this study, the 1999 Chi-Chi earthquake, which occurred once in a century, was selected as the base period for landslide evolution (Figure 2).
Glaciers and glaciation of North Island, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Shaun R. Eaves, Martin S. Brook
The Tararua Range is situated in the lower North Island, extending ∼100 km NNE-SSW (Figure 1). The range is narrow (spanning 10–30 km) and steep, rising from near sea level to a maximum elevation of 1571 m asl (Mitre Peak). Several peaks in the centre of the range exceed 1500 m asl, and the topography of the range is deeply entrenched, with rivers draining east and west from the range axis. Adkin (1911) was first to note the U-shaped appearance of upper Park Valley and several other valley heads in the central Tararuas. Shepherd (1987) considered that the evidence for glacial activity had been overstated by Adkin (1911). Quantitative analysis of cross-valley profiles later supported Adkin’s (1911) early observations, and expanded the potential extent of former Tararua glaciers (Brook et al. 2005; Brook and Brock 2005). Brook and Kirkbride (2018) then reported the presence of a small cirque-like basin on the eastern flank of Mt Aston, 25 km southwest of the glaciated sites in the central Tararuas. Nevertheless, the majority of palaeoglaciological research in this region has occurred at the head of Park Valley (Figure 11). Park Valley is situated on the eastern side of drainage divide, forming the headwaters of the Waiohine River – a tributary of the Ruamahanga River, the largest river of the lower North Island. Park Valley is backed by several peaks, the highest of which is Arete at 1505 m asl (Figure 11).
LiDAR-based mapping of paleo-ice streams in the eastern Great Lakes sector of the Laurentide Ice Sheet and a model for the evolution of drumlins and MSGLs
Published in GFF, 2018
Shane Sookhan, Nick Eyles, Niko Putkinen
The Allegheny Plateau is underlain by gently westward-dipping Devonian strata whose northern margin is delineated by outcrops of resistant lower Devonian limestones which give rise to the Onondaga Escarpment. The surface of the plateau displays a well-developed and presumably long-lived, trellised and dendritic fluvial drainage system that has been variably affected by glacial erosion and deposition. LIDAR data now allow more detailed mapping than hitherto possible of drumlinized rock and serrated (drumlinized) interfluves cut by ice flowing across the plateau to the late Wisconsinan glacial limit in Pennsylvania defined by the so-called “Terminal Moraine” (Carvill Lewis 1883, Fig. 4). Glacial erosion has been most intense along the northern and western flanks of the Allegheny Plateau where the original dendritic system has been smoothed and subdued by glacial erosion and mantled with drift. This is most clearly seen on the Salamanca re-entrant south of Batavia in New York State, and on the plateau surfaces surrounding the Finger Lakes which occupy a large bowl-shaped glacially scoured area of the plateau between Batavia in the west and Syracuse in the east (Fig. 1). Along the northern margins of the plateau, the drainage divides between long south-draining valleys of the Susquehanna River system and much shorter north-draining valleys flowing off the Plateau were breached to form continuous “through valleys” that now cut through the face of the escarpment (see Coates 1974). Glacial erosion has overdeepened several of these valleys that are now occupied by eleven so-called “finger lakes”, the largest of these (Otisco, Skaneateles, Owasco, Cayuga, Seneca, Keuka, Canandaigua; Fig. 2) have been greatly modified by glacial erosion and the bedrock floors of Canandaigua, Seneca and Cayuga lakes are over-deepened well below sea level (−151, −306, −242 m, respectively; Mullins & Eyles 1996). These basins form a distinct radiating pattern that converges northwards in the vicinity of Rochester and the deepest part of Lake Ontario (the Rochester Basin at −244 m below sea level) implying a related glacial erosional origin. Four smaller and much shallower lake basins occur to the west (Conesus, Hemlock, Canadice and Honeoye). Very thick (200 m; Wellner et al. 1996) gravel-cored hummocky kame and kettle topography of the VHM occurs at the southern ends of the Fingers Lakes. This records rapid ice-contact subaqueous deposition from meltwaters at the margins of narrow ice lobes that ponded an extensive system of proglacial lakes north of the drainage divide with the Susquehanna River system (Coates 1974). VHM chokes many through valleys and now forms the modern drainage divide between waters draining north to Lake Ontario and south to the Susquehanna River.