Channel straightening in a naturally meandering river is a common historical trigger of channel incision which typically results in stream bank destabilization. Several of the larger river systems in the upland portio...Channel straightening in a naturally meandering river is a common historical trigger of channel incision which typically results in stream bank destabilization. Several of the larger river systems in the upland portion of the Yazoo River Basin have subjected channelization resulting in profound changes in the physical and geomorphological characteristics of these systems. Fish were sampled using electroshocking gear and hoop nets to evaluate the impact of stream bank destabilization and loss of habitat heterogeneity resulting from channelization on fish communities. While distinct differences in the fish communities were evident, only the Skuna appeared to have characteristics of a damaged system. More than 95% of the biomass was comprised of species reaching an adult length of less than 300 mm. The lotic omnivorous fishes that dominated the biomass from Skuna are often associated with smaller streams rather than rivers. Furthermore, 72% of the catch consisted of fish preferring littoral zone habitats. The shallow depth and lack of woody debris in Skuna provided a selective advantage for smaller species of fish that could use shoreline habitats as protection from the current. Based on results from the Skuna River, channel straightening that leads to channel incision, bank failure and over widening provide habitats too shallow to support a community of fishes typical of northern Mississippi riverine system. This information may be useful in making comparison of damaged riverine ecosystems and assist managers in determining impairment and success in the TMDL （Total Maximum Daily Load） process.展开更多
Over 40 billion tons of sand is mined worldwide every year which isestimated to be higher than the natural replacement rates. In Kenya, therate of sand mining is raising concerns over its environmental effects sinceit...Over 40 billion tons of sand is mined worldwide every year which isestimated to be higher than the natural replacement rates. In Kenya, therate of sand mining is raising concerns over its environmental effects sinceit is not regulated. This paper presents findings on the geomorphic effectsof sand mining in the ephemeral River Tyaa channel in Kitui County. Thestudy adopts the concept of feedback response mechanism of a naturalgeomorphic system. Through purposive sampling River Tyaa was selectedfor the study, where rampant sand mining was reportedly taking place.Random sampling on the five sand mining sites identified came up with arepresentative site namely Kanginga on which systematic sampling wasapplied while collecting data at both the active and control sites. Dataon channel width, depth and slope angles was obtained through physicalmeasurements while data on quantity of sand mined was obtained fromMwingi Sand Mining Cooperative. Multiple logistic regression analysiswas used to analyse data whereby the model compared active and controlsites. Test results indicated that sand mining had significantly increasedriver channel’s width (O.R. =1.531), depth (O.R. =1.527) and slope angles(O.R. =1.634) at active mining sites compared to control sites as deducedfrom the respective Odds Ratios. It concluded that sand mining had alteredchannel’s morphology resulting to adverse environmental effects such asloss of riparian vegetation and channel incision. It recommended curbingof illegal sand mining through licencing operators and reducing quantity ofsand mined by closing some mines. Furthers, it recommended monitoringthrough regular Environmental Impact Assessment (E.I.A) and Audit (E.A)to inform protection of the river system from degrading.展开更多
Bed structures in many mountain rivers provide additional resistance to the flow. A field experiment was conducted on debris flow deposits in the valley of the Jiangjiagou Ravine, a tributary of the Yangtze River in s...Bed structures in many mountain rivers provide additional resistance to the flow. A field experiment was conducted on debris flow deposits in the valley of the Jiangjiagou Ravine, a tributary of the Yangtze River in southwestern China, to study the evolution and distribution of bed structures and their relationship with environmental conditions. Water and sediment from the Jiangjiagou main stream were diverted into the experimental channel. Several hydrological schemes were adopted to scour the channel until equilibrium was reached. During this process the evolutions of bed structures and channel configuration were investigated. The results indicate that stronger bed structures mean greater stream power consumption, greater resistance, and greater slope in a certain section when rivers are in dynamic equilibrium. Thus, to some extent the longitudinal profiles of channels can be determined by the distribution of bed structures. In natural cases, the strength and evolution of bed structures are under the influence of environmental conditions such as discharge and bed-load transportation rate. That is, given the same conditions, the same bed structure distribution and longitudinal profile can be predicted.展开更多
Based on analysis of drilling, logging and field profile data, six sequence boundaries in Permian are identified in Bachu and Tazhong regions of Tarim Basin. All sequence boundaries are of type I sequence bound- aries...Based on analysis of drilling, logging and field profile data, six sequence boundaries in Permian are identified in Bachu and Tazhong regions of Tarim Basin. All sequence boundaries are of type I sequence bound- aries, and are characterized by down cut. According to the six sequence boundaries, the Permian in this area can be divided into 5 third-order sequences, and all the sequences correspond with classic sequence model of Vail. Sequence Psq4 indicates lake transgressive system tract （TST） and highstand system tract （HST）. Se- quences Psql, Psq2, Psq3, Psq5 indicate low stand system tract （ LST）, transgressive system tract and high- stand system tract. LST is deposited by incised channel infilling with features of fluvial facies. TST is deposited by shore-shallow lake and semi-deep lake. HST is deposited by semi-deep lake, shore-shallow lake and delta. In addition, volcanic rocks are present on the top part of HST in sequence Psq3. Incised channel infilling and deltaic deposits were mainly distributed on western slope of Tadong uplift.展开更多
文摘Channel straightening in a naturally meandering river is a common historical trigger of channel incision which typically results in stream bank destabilization. Several of the larger river systems in the upland portion of the Yazoo River Basin have subjected channelization resulting in profound changes in the physical and geomorphological characteristics of these systems. Fish were sampled using electroshocking gear and hoop nets to evaluate the impact of stream bank destabilization and loss of habitat heterogeneity resulting from channelization on fish communities. While distinct differences in the fish communities were evident, only the Skuna appeared to have characteristics of a damaged system. More than 95% of the biomass was comprised of species reaching an adult length of less than 300 mm. The lotic omnivorous fishes that dominated the biomass from Skuna are often associated with smaller streams rather than rivers. Furthermore, 72% of the catch consisted of fish preferring littoral zone habitats. The shallow depth and lack of woody debris in Skuna provided a selective advantage for smaller species of fish that could use shoreline habitats as protection from the current. Based on results from the Skuna River, channel straightening that leads to channel incision, bank failure and over widening provide habitats too shallow to support a community of fishes typical of northern Mississippi riverine system. This information may be useful in making comparison of damaged riverine ecosystems and assist managers in determining impairment and success in the TMDL （Total Maximum Daily Load） process.
文摘Over 40 billion tons of sand is mined worldwide every year which isestimated to be higher than the natural replacement rates. In Kenya, therate of sand mining is raising concerns over its environmental effects sinceit is not regulated. This paper presents findings on the geomorphic effectsof sand mining in the ephemeral River Tyaa channel in Kitui County. Thestudy adopts the concept of feedback response mechanism of a naturalgeomorphic system. Through purposive sampling River Tyaa was selectedfor the study, where rampant sand mining was reportedly taking place.Random sampling on the five sand mining sites identified came up with arepresentative site namely Kanginga on which systematic sampling wasapplied while collecting data at both the active and control sites. Dataon channel width, depth and slope angles was obtained through physicalmeasurements while data on quantity of sand mined was obtained fromMwingi Sand Mining Cooperative. Multiple logistic regression analysiswas used to analyse data whereby the model compared active and controlsites. Test results indicated that sand mining had significantly increasedriver channel’s width (O.R. =1.531), depth (O.R. =1.527) and slope angles(O.R. =1.634) at active mining sites compared to control sites as deducedfrom the respective Odds Ratios. It concluded that sand mining had alteredchannel’s morphology resulting to adverse environmental effects such asloss of riparian vegetation and channel incision. It recommended curbingof illegal sand mining through licencing operators and reducing quantity ofsand mined by closing some mines. Furthers, it recommended monitoringthrough regular Environmental Impact Assessment (E.I.A) and Audit (E.A)to inform protection of the river system from degrading.
基金supported by the National Natural Science Foundation of China (Grant No.51009096)the Research Fund of Nanjing Hydraulic Research Institute (Grant No.Y210003)
文摘Bed structures in many mountain rivers provide additional resistance to the flow. A field experiment was conducted on debris flow deposits in the valley of the Jiangjiagou Ravine, a tributary of the Yangtze River in southwestern China, to study the evolution and distribution of bed structures and their relationship with environmental conditions. Water and sediment from the Jiangjiagou main stream were diverted into the experimental channel. Several hydrological schemes were adopted to scour the channel until equilibrium was reached. During this process the evolutions of bed structures and channel configuration were investigated. The results indicate that stronger bed structures mean greater stream power consumption, greater resistance, and greater slope in a certain section when rivers are in dynamic equilibrium. Thus, to some extent the longitudinal profiles of channels can be determined by the distribution of bed structures. In natural cases, the strength and evolution of bed structures are under the influence of environmental conditions such as discharge and bed-load transportation rate. That is, given the same conditions, the same bed structure distribution and longitudinal profile can be predicted.
文摘Based on analysis of drilling, logging and field profile data, six sequence boundaries in Permian are identified in Bachu and Tazhong regions of Tarim Basin. All sequence boundaries are of type I sequence bound- aries, and are characterized by down cut. According to the six sequence boundaries, the Permian in this area can be divided into 5 third-order sequences, and all the sequences correspond with classic sequence model of Vail. Sequence Psq4 indicates lake transgressive system tract （TST） and highstand system tract （HST）. Se- quences Psql, Psq2, Psq3, Psq5 indicate low stand system tract （ LST）, transgressive system tract and high- stand system tract. LST is deposited by incised channel infilling with features of fluvial facies. TST is deposited by shore-shallow lake and semi-deep lake. HST is deposited by semi-deep lake, shore-shallow lake and delta. In addition, volcanic rocks are present on the top part of HST in sequence Psq3. Incised channel infilling and deltaic deposits were mainly distributed on western slope of Tadong uplift.
