Guo-an Yu

Restoration of an incised mountain stream using artificial step-pool system

A field experiment using an artificial step-pool system was conducted to restore the Diaoga River, a seriously incised mountain stream in Yunnan-Guizhou Plateau, southwest China. Twenty-four artificial steps, designed to mimic natural step forms, were constructed on three stretches of about 260 m length in the middle reach of the river. Channel topography, hydraulic features, aquatic habitats and stream ecology were monitored for 20 months. Following the construction of the artificial step-pool system, the stream bed development coefficient increased significantly. This indicates that actions helped to dissipate flow energy more effectively, enhancing the stability of the stream bed. The step-pools have effectively controlled the incision and stabilized the river morphology. In addition, they have created multiple habitats for different species and increased the habitat diversity. Improvement of the aquatic ecosystem is confirmed by increased density and taxa richness of benthic macro-invertebrates, which are used as an indicator species to evaluate stream ecology.

A broad overview of landscape diversity of the Yellow River source zone

Pronounced variability in the landscapes of the upper Yellow River basin reflects complex inter-relationships between tectonics, climate and surficial processes over time. While the process of landscape classification necessarily involves assumptions and the simplification of reality, it still provides a useful organizational framework within which the nature and controls upon these relationships can be examined. This paper groups the landscapes of the Yellow River source zone into 10 primary classes through GIS analysis of global SRTM 90 m DEM. Landscapes of this region range from the high-elevation, low-relief plains of the upper plateau, through the narrow high-relief valleys of the Anyemaqen Shan (Mountains) in the central basin, to the dramatically incised landscapes within the Tongde and Gonghe sedimentary basins at the downstream end of the study area. A description of each of the landscape classes is presented and the interplay between tectonics, climate and surficial processes over time is examined. The importance of placing the landscapes into the context of the evolutionary history of the Yellow River source zone is emphasized, in particular the evolution of the drainage system and its influence upon present landscape dynamics.

Geomorphic Diversity of Rivers in the Upper Yellow River Basin

The Yellow River is the third longest river in Asia and the sixth longest river in the world. The Upper Yellow River lies at the margins of and atop the Qinghai–Tibet Plateau, the highest plateau in the world with an average elevation of 4000 m above sea level and an area of about 2.6 million km2. This area contributes about 56 % of the total run-off, but only 10 % of sediment load of the whole river basin. The river has a strong monsoon-driven seasonality in discharge, with around 60 % of annual run-off and 80 % of annual sediment discharge occurring during the flood season (June-September, especially July). Other than the impacts of a small (but increasing) number of dams along the trunk stream and tributaries close to the plateau margin, the flow regime of the Upper Yellow River is largely unregulated. Rivers of the Upper Yellow River Basin are globally significant examples of river response to tectonic uplift and incision. This chapter documents a ‘journey along the Upper Yellow River’, providing an account of river diversity and assessing controls upon the pattern of river types. Valley gradient and confinement are the primary controls on river diversity and evolution in this area. Adjacent to the Qinghai–Gansu border, tectonic uplift and climate changes have induced river bed incision via knickpoint retreat, cutting back through bedrock gorges and basin fills. An elevation (climate) induced gradient of riparian vegetation cover exerts a critical control upon the pattern of channel planform types along the river.

Analysis of controls upon channel planform at the First Great Bend of the Upper Yellow River, Qinghai-Tibet Plateau

The 270 km long section of the Upper Yellow River at the First Great Bend is comprised of single channel and multiple channel systems that alternate among anastomosing, anabranching, meandering and braided reaches. The sequence of downstream pattern changes is characterized as: anastomosing-anabranching, anabranching-meandering, meandering-braided and braided-meandering. Remote sensing images, DEM data and field investigations are used to assess and interpret controls on these reach transitions. Channel slope and bed sediment size are key determinants of transitions in channel planform. Anastomosing reaches have a relatively high bed slope (0.86‰) and coarser sediment bed material (d50 = 3.5 mm). In contrast, meandering reaches have a low slope (0.30‰) and fine sediment bed material (d50 = 0.036 mm). The transition from a meandering to braided pattern is characterized by an increase in channel width-depth ratio, indicating the important role of bank strength (i.e. cohesive versus non-cohesive versus channel boundaries). Interestingly, the braided-meandering and meandering-braided transitions are coincident with variable flow inputs from tributary rivers (Baihe and Heihe rivers respectively). Theoretical analysis of the meandering-braided transition highlights the key control of channel width-depth ratio as a determinant of channel planform.

An exploratory analysis of benthic macroinvertebrates as indicators of the ecological status of the Upper Yellow and Yangtze Rivers

This study presents findings of the first systematic analysis of aquatic biotic assemblages in the source region of the Yellow and Yangtze Rivers. It provides an initial basis with which to select representative organisms as indicators to assess the aquatic ecological status of rivers in this region. Macroinvertebrates are considered to be good indicators of long-term environmental changes due to their restricted range and persistence over time. Field investigations of macroinvertebrates were conducted in August 2009 in the source region of the Yellow River, and in July 2010 in the source region of the Yangtze River. Altogether 68 taxa of macroinvertebrates belonging to 29 families and 59 genera were identified. Among them were 8 annelids, 5 mollusks, 54 arthropods and 1 other animal. In the source region of the Yellow River, taxa number, density and biomass of macroinvertebrates were 50, 329 individuals m−2 and 0.3966 g dry weight m−2, respectively. Equivalent figures for the source region of the Yangtze River were 29, 59 individuals m−2 and 0.0307 g dry weight m−2. The lower benthic animal resources in the source region of the Yangtze River are ascribed to higher altitude, higher sediment concentration and wetland degradation. Preliminary findings of this exploratory study indicate that hydroelectric power stations had a weak impact on benthic dwellers but wetland degradation caused by a series of human activities had a catastrophic impact on survival of macroinvertebrates. Ecological protection measures such as conservative grazing and vegetation management are required to minimize grassland degradation and desertification, and reduce soil erosion rate and river sediment discharge.

Fluvial diversity in relation to valley setting in the source region of the Yangtze and Yellow Rivers

The spatial distribution of valley setting (laterally-unconfined, partly-confined, or confined) and fluvial morphology in the source region of the Yangtze and Yellow Rivers is contrasted and analyzed. The source region of the Yangtze River is divided into 3 broad sections (I, II and III) based on valley setting and channel gradient, with the upstream and downstream sections being characterized by confined (some reaches partly-confined) valleys, while the middle section is characterized with wide and shallow, laterally-unconfined valleys. Gorges are prominent in sections I and III, while braided channel patterns dominate section II. By contrast, the source region of the Yellow River is divided into 5 broad sections (sections I–V) based on valley characteristics and channel gradient. Sections I, II and IV are alluvial reaches with mainly laterally-unconfined (some short reaches partly-confined) valleys. Sections III and V are mainly confined or partly-confined. Greater morphological diversity is evident in the source region of the Yellow River relative to the upper Yangtze River. This includes braided, anabranching, anastomosing, meandering and straight alluvial patterns, with gorges in confined reaches. The macro-relief (elevation, gradient, aspect, valley alignment and confinement) of the region, linked directly to tectonic movement of the Qinghai-Tibet Plateau, tied to climatic, hydrologic and biotic considerations, are primary controls upon the patterns of river diversity in the region.

Stream networks and knickpoints in the Sanjiangyuan Region

Stream networks and knickpoints in the Sanjiangyuan Region The source area of the Lancang (Mekong), Yangtze and Yellow rivers is named in Chinese Sanjiangyuan (source of three rivers). Geographical characteristics of these rivers, and various rivers at the margin of the Qinghai-Tibetan Plateau (Jialing, Minjiang, Dadu, Yalong and Jinsha) are summarized from field investigations along with digital elevation model (DEM) analyses and satellite images. Uplift of the Qinghai-Tibetan Plateau has resulted in an asymmetrical distribution of tributaries for stream networks at the margins of the plateau. Almost all tributaries join the trunk stream from the northwest. Three types of drainage network are evident: plume, nervation and dendritic. In general, plume networks have a large number of first order streams. Nervation networks have a main stream and parallel tributaries. Dentritic networks are characrterized by continuous bifurcation and have a branch-like appearance. Most stream networks in the Sanjiangyuan region are of the nervation type. Several large knickpoints are evident along the longitudinal profiles of the Yellow and Yangtze Rivers. Channel aggradation immediately upstream of these knickpoints marks a transition in river processes from vertical bed evolution (i.e. incision) to horizontal channel adjustment (and associated braided and anabranching channels). Rozwój progów skalnych oraz morfologia rzek w regione Sanjiangyuan W artykule przedstawiono proces rozwoju progów skalnych wzdłuż rzek Yellow i Yangtze. Wykazano wpływ progów skalnych na zmiany morfologiczne dna koryt rzek. Głównie skoncentrowano się na zmianach agradacyjnych powyżej omawianych progów. Progi te są wyznacznikami zmian charakteru koryta rzecznego, z pionowo wciętego na wielonurtowy, roztopowy o szerszym korycie. Badania wykonano w rejonie Qinghai_Tibetan Plateau, zwanym obszarem źródłowym trzech rzek - oprócz wyżej wspomnianych również rzeka Mekong.