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1.
In the absence of long-term hydrologic and streamflow records an understanding of river morphology (present and past) can help delineate changes in magnitudes of water and sediment discharges. The relict drainage system of Gujarat alluvial plain provides an opportunity to reconstruct the palaeochannel morphology-related discharge estimations. In this paper, based on the geomorphological evidence and channel geometry, an attempt has been made to reconstruct the palaeohydrological condition in the Shedhi River during the Holocene. A comparison of the present day channel of the Shedhi River with that of its palaeo counterpart reveals that the former was carrying much higher bankfull discharge (∼5500m3 s−1) as compared to the present (∼200m3 s−1). This is attributed to a larger drainage area and enhanced precipitation in the Shedhi River basin.  相似文献   

2.
Stability of landslide dams and development of knickpoints   总被引：2，自引：0，他引：2  
The Wenchuan earthquake triggered many landslides and numerous avalanches and created 100 odd quake lakes. The quake lakes may be removed or preserved. The removal strategy was applied to several large landslide dams, which were dangerous because massive amounts of water pooled up in the quake lakes. The dams could eventually fail under the action of dam outburst flooding, potentially endangering the lives of people in the downstream reaches. This paper studied the stability of landslide dams and the development of knickpoints by field investigations and experiments, and analyzing satellite images. The study concluded that if landslide dams were preserved, they would develop into knickpoints and act as a primary control of riverbed incision and, thus, reduce the potential of new landslide. The stability of landslide dams depends mainly on the development of the step-pool system and stream power of the flood flow. If a landslide dam consists of many boulders, a step-pool system may develop on the spillway channel of the dam, which would maximize the resistance, consume most of the flow energy and consequently protect the dam from incision. The development degree of the step-pool system is represented by a parameter S p, which was measured with a specially designed instrument. A preservation ratio of landslide dams is defined as the ratio of preserved height after flood scouring to the original height of the dam. For streams with peak flood discharge lower than 30 m3/s, the preservation ratio is linearly proportional to S p. For rivers with a peak flood discharge higher than 30 m3/s (30–30,000 m3/s), the minimum S p value for stable channel increases with log p, in which p is the unit stream power. For a landslide dam with a poorly developed step-pool system, S p is smaller than the minimum value and the outburst flood incises the spillway channel and causes failure of the dam. For preserved landslide dams, sediment deposits in the quake lakes. A landslide dam may develop into a knickpoint if it is stabilized by long-term action of the flow. Large knickpoints can totally change the fluvial processes and river morphology. Uplift of the Qinghai–Tibetan Plateau has caused extensive channel bed incision along almost all rivers. For many rivers, the incision has been partly controlled by knickpoints. Upstream reaches of a knickpoint have a new and unchanging base level. This brings about a transition from degradation to aggradation and from vertical bed evolution to horizontal fluvial process. Multiple and unstable channels are prominent in the reaches, upstream of the knickpoints. If hundreds of landslide dams occurred simultaneously on a reach of a mountain river, the potential energy of bank failure and the slope erosion would be greatly reduced and sediment yield from the watershed may be reduced to nearly zero. The quake lakes may be preserved long term and become beautiful landscapes. Streams with long-term unfilled quake lakes have good aquatic ecology.  相似文献   

3.
The Burdekin River is an example of a class of tropical streams which experience two to four orders of magnitude variation in discharge, in response to seasonal but erratic monsoonal rainfall. Floods of the Burdekin rise abruptly, reaching peak discharges of up to 40,000 m3 s-1 in less than 24 h; maintain peak flow for up to a few days, and recede exponentially. The geomorphology and deposits of these rivers reflect the extreme discharge fluctuations, and have not previously been described. A stretch of the upper Burdekin River comprising four bends and one straight reach was examined near the town of Charters Towers. The river bed is largely exposed for most of any year, with a small, misfit perennial channel carrying low stage flow. Major geomorphic elements of bends include point bars with ridge-and-swale topography, three distinct types of chute channels, avalanche slipfaces up to 5 m or more high around the downstream edges of bars, and on the outer part of one point bar an elevated, vegetated ridge. Straight reaches are flat or gently inclined, sand- and gravel-covered surfaces. Much of the river bed is covered by well sorted, in places gravelly, coarse to very coarse-grained sand with local accumulations of pebble to boulder gravel. Lower parts of the river bed are periodically draped by mud which is desiccated on exposure. Dunes and plane beds are the most commonly occurring bedforms, with local development of gravelly antidunes. Most bank tops and upper, vegetated bars are covered by silt and fine-grained sand. The river bed also hosts a low-diversity but locally high-abundance, flood-tolerant flora dominated by the paperbark tree Melaleuca argentea, which plays an important role in controlling the distribution of sediment. The gross geomorphology of the river bed and most of the sedimentary features are interpreted as having formed during major (bankfull or near bankfull) flows, which have a recurrence of about 18 years (based on 65 years hydrographic data). The initial rapid drop in discharge following flood peaks appears to preserve flood peak features on upper bars more or less intact, whereas lower areas are subjected to variable degrees of modification during falling stage and by more frequent, non-bankfull discharge events.  相似文献   

4.
河道过流能力与主槽形态有关，而主槽形态又取决于上游水沙条件，分析过流能力与这两者之间的关系对研究黄河下游游荡段河床演变规律有重要意义。从典型断面和河段平均两个尺度，定量分析了黄河下游游荡段1986—2015年平滩流量与水沙条件（来沙系数和水流冲刷强度）及汛前主槽形态（河相系数）之间的响应关系。结果表明：① 1986年至小浪底水库运行前，游荡段淤积严重，主槽萎缩，河道过流能力急剧下降，自小浪底水库运行后，游荡段发生强烈冲刷，其断面持续趋向窄深，过流能力逐年恢复；②建立了断面和河段平滩流量与水沙条件及河相系数的幂函数关系，二者相关系数均在0.5以上，但河段尺度相比于断面尺度的相关系数至少可提高17%；③河段平滩流量与前5年汛期平均水流冲刷强度及河相系数的相关系数接近0.94，相应计算公式能较好地反映平滩流量的变化过程，为分析其他河段平滩流量的变化提供了参考方法。  相似文献   

5.
河道过流能力与主槽形态有关,而主槽形态又取决于上游水沙条件,分析过流能力与这两者之间的关系对研究黄河下游游荡段河床演变规律有重要意义。从典型断面和河段平均两个尺度,定量分析了黄河下游游荡段1986-2015年平滩流量与水沙条件(来沙系数和水流冲刷强度)及汛前主槽形态(河相系数)之间的响应关系。结果表明:①1986年至小浪底水库运行前,游荡段淤积严重,主槽萎缩,河道过流能力急剧下降,自小浪底水库运行后,游荡段发生强烈冲刷,其断面持续趋向窄深,过流能力逐年恢复;②建立了断面和河段平滩流量与水沙条件及河相系数的幂函数关系,二者相关系数均在0.5以上,但河段尺度相比于断面尺度的相关系数至少可提高17%;③河段平滩流量与前5年汛期平均水流冲刷强度及河相系数的相关系数接近0.94,相应计算公式能较好地反映平滩流量的变化过程,为分析其他河段平滩流量的变化提供了参考方法。  相似文献   

6.
张金良  鲁俊 《水科学进展》2021,32(2):192-200
黄河上游内蒙古冲积性河道凌汛问题突出,研究河道冲淤演变与凌情响应机制可为该河段防凌减灾提供技术支持。根据内蒙古河段凌情、河道冲淤演变资料,分析凌情变化表征指标及与之密切相关的河道冲淤演变特征指标,研究河道冲淤演变特征指标与凌情变化表征指标的响应关系。结果表明:河道冲淤演变的特征指标平滩流量与凌情表征指标冰下过流能力、槽蓄水增量关系密切,冰下过流能力为平滩流量的1/5左右,随着平滩流量减小而减小,而槽蓄水增量随着平滩流量的减小而增大,有利内蒙古河段防凌的平滩流量宜不小于2 000 m3/s,槽蓄水增量宜不超过14亿m3。本研究成果可为内蒙古河段冰凌灾害防治提供参考。  相似文献   

7.
Some drainage ditches in the intensively managed row-crop agricultural region of southern Minnesota evolved from a trapezoidal form to multi-staged channel forms similar to natural streams. Older ditches constructed in cohesive sediment of the Des Moines Lobe till tend to follow a channel evolution model developed by Simon and Hupp. Site cross sections, longitudinal water and bed profiles and bed material particle size were determined according to Harrelson and others at 24 older ditch reaches, 5 newly constructed ditch reaches and 13 natural stream reaches. Morphological features were hypothesized to change from trapezoidal form to flat bench banks, similar to benches found in natural stream channels. All data were statistically analyzed with respect to drainage area using regression, because channel form is directly related to drainage area for a given climate, geology and land use. Results show similar regression slope and intercept for bankfull channel width and bankfull cross-sectional area (CSA) of older ditches and natural streams compared to typical trapezoidal designed ditches. Evolved ditches developed a small floodplain bench above the ditch bed and adjusted their bankfull widths similar to natural stream channels with respect to drainage area. Old ditches showed a relatively strong R 2 (0.82, 0.68) for channel CSA and width, a weaker R 2 (0.45) for water surface slope, and little to no correlation with bed particle size. Channel form appears to have adjusted more quickly than bed facets and/or bed particle size distribution. However, stepwise regression determined that D84, width/depth ratio and mean bankfull depth explained 83?% of the variability of channel features across varying drainage areas. Findings suggest a possible reduction of long-term maintenance costs if older ditches are allowed to evolve over time. A stable ditch form similar to natural streams is typically self-sustaining, suggesting that prior to a scheduled clean-out, the ditch should be examined for hydraulic capacity, sediment transport and bank stability.  相似文献   

8.
Bankfull discharge is a comprehensive factor reflecting the channel-forming capability of water flow and the flood and sediment transport capacity of a river channel. It is based on the interaction of the flow, sediment, and river channel, of which flow and sediment conditions play crucial roles. Using data recorded since the 1950s, this paper analyses statistically, the characteristics and variations of bankfull discharge at two stations on the Inner Mongolian reaches of the upper Yellow River. Results indicate that flood season variations in bankfull discharge are nonlinear and are governed by flood peak discharge, mean discharge, and the mean incoming sediment coefficients. Variation in bankfull discharge is related not only to the flow and sediment conditions of the current year but also to those of previous years. The 10-year moving average of flow and sediment conditions can be representative of present and previous years. By considering flood season peak discharge and incoming sediment coefficients as independent impact factors, a formula is derived to determine bankfull discharge. The results can be used to predict the bankfull discharge of the Yellow River channel in Inner Mongolia under specific flow and sediment conditions and provide reference for the purpose of further study related to restoring and maintaining the basic functions of the river channel regarding flood discharge and sediments.  相似文献   

9.
The USA Clean Water Act requires the development of a total maximum daily load (TMDL) when Minnesota’s water quality standard for turbidity is exceeded; however, regions underlain with fine-grained lacustrine deposits yield large natural background loads of suspended inorganic sediment. A review of hydrogeologic pathways was conducted along with the statistical analysis of geomorphic metrics, collected at 15 sites with varying drainage areas in the upper Nemadji River basin, northeastern Minnesota. Regression analysis indicated a strong linkage between bankfull cross-sectional area and drainage area. Dimensionless geomorphic metric ratios were developed to predict channel evolution potential and associated channel erosion risk. Sites located in drainage areas less than 2 km2 had low erosion risk and showed a correlation between channel slope and relative roughness (D 84/mean bankfull channel depth, 88%). A principal components analysis explained over 98% of the variance between sites and indicated five important channel shape metrics to predict channel erosion: bankfull width, bankfull depth, maximum depth, cross-sectional area, and valley beltwidth. Mass wasting of cohesive stream channel sediment was influenced by groundwater discharge and produced turbid waters in the upper Nemadji River.  相似文献   

10.
Understanding the spatial distribution and variability of geochemical tracers is crucial for estimating groundwater influxes into a river and can contribute to better future water management strategies. Because of the much higher radon (222Rn) activities in groundwater compared to river water, 222Rn was used as the main tracer to estimate groundwater influxes to river discharge over a 323-km distance of the Big Sioux River, eastern South Dakota, USA; these influx estimates were compared to the estimates using Cl? concentrations. In the reaches overall, groundwater influxes using the 222Rn activity approach ranged between 0.3 and 6.4 m3/m/day (mean 1.8 m3/m/day) and the cumulative groundwater influx estimated during the study period was 3,982–146,594 m3/day (mean 40,568 m3/day), accounting for 0.2–41.9% (mean 12.5%) of the total river flow rate. The mean groundwater influx derived using the 222Rn activity approach was lower than that calculated based on Cl? concentration (35.6 m3/m/day) for most of the reaches. Based on the Cl? approach, groundwater accounted for 37.3% of the total river flow rate. The difference between the method estimates may be associated with minimal differences between groundwater and river Cl? concentrations. These assessments will provide a better understanding of estimates used for the allocation of water resources to sustain agricultural productivity in the basin. However, a more detailed sampling program is necessary for accurate influx estimation, and also to understand the influence of seasonal variation on groundwater influxes into the basin.  相似文献   

11.
张为  高宇  许全喜  袁晶 《水科学进展》2018,29(3):331-338
随着三峡水库的运用,其下游的造床流量发生变化,研究坝下游造床流量的变化特性及主要影响因素对河道的冲淤特性及河床演变机理研究有着重要意义。根据1981—2015年的资料,采用平滩水位法、马卡维耶夫法和流量保证率法计算三峡水库蓄水前后宜昌、枝城、沙市、监利、螺山、汉口、九江、大通各站的造床流量。结果表明:①马卡维耶夫法同时考虑了流量过程和输沙能力的影响,计算结果相对合理。②蓄水后各站造床流量减小3 000~6 000 m3/s,符合坝下游主要冲淤变形部位由平滩河槽调整为中枯水河槽的变化特性,反映了结果的合理性。具体来看,时间上,2009年以后造床流量的减小趋势更为明显;空间上,从绝对值来看,以监利站为转折点,从宜昌至大通呈先减小后增大的趋势。③造床流量对来水量和洪峰流量的响应较为敏感,与之呈正相关关系。  相似文献   

12.
Multiple streamflow measurements were made at coupled discharge measurement stations to quantify rates of aquifer recharge and discharge on two reaches of the Souhegan River, New Hampshire, USA, flowing within a glacial-drift river-valley aquifer. The reaches included a predominantly losing (aquifer recharge) reach and a variable (aquifer recharge and discharge) reach located downstream of the former reach. River leakage, the differential between coupled upstream and downstream streamflow measurements along a reach, varied by almost 30 cubic feet per second (ft3/s) (0.85 m3/s) along the two reaches. The upper reach averaged 3.94 ft3/s (0.11 m3/s) loss whereas the lower reach averaged 4.85 ft3/s (0.14 m3/s) gain. At the upper reach, 13 losses were measured out of 19 coupled measurements. At the lower reach, ten out of 13 coupled measurements indicated gains in flow and suggest that this reach is primarily a gaining river reach. An important factor in river leakage appears to be antecedent trends in river stage. At the upper reach, gains were measured only during periods of declining river stage. Conversely, at the lower reach, streamflow loss was measured primarily during periods of rising river stage. Although some tendencies exist, several factors complicate the analysis of river leakage, most notably the inaccuracies in computed stream discharge.  相似文献   

13.
藏东南部泥石流堵河试验研究   总被引：4，自引：0，他引：4  
通过模型试验对泥石流入汇主河后堵塞坝形成过程以及堵塞坝体溃决后主河河床形态特征进行了研究。实验历时3个月,共13组试验。在支主沟交汇角为90°的情况下,通过改变支沟泥石流容重、支主沟的流量比和动量比,建立了泥石流堵河的判别公式,当r>1 001.16时容易发生堵河现象,并对培龙沟两次泥石流堵河事件进行了判定;定义了主河的束窄率S与主河流速变异系数Fv,并发现了主河的束窄率与支主沟动量比之间存在线性关系;主河稳定后的平均宽度与流速变异系数之间存在幂的关系。该实验能够较好地模拟泥石流堵塞坝形成的过程,结果比较合理,并为泥石流灾害的防治提供了相应的理论基础。  相似文献   

14.
Effects of sediment extraction and dam construction on changes of riverbed characteristics over yearly to decadal scales in the lower Tedori River of Japan are clarified. Over 1950–1991, the riverbed degraded in excess of 0.5–3.5 m. Concurrently, riverbed sediment volume of the 0–16 km reach decreased by 12.7 × 106 m3. Intensive sediment extraction was the dominant cause of riverbed degradation during the period. During 1991–2007, an increase in riverbed sediment volume of 0.6 × 106 m3 resulted in accretion of the riverbed by average depth 0.04 m. The cessation of sand and gravel mining (SGM), coupled with Tedorigawa Dam operation since 1980, was responsible for that accretion. Temporal change in riverbed elevation during 1950–2007 indicates that there were five phases of vertical adjustment. Combination of nonlinear regression models described four of these phases well. During 1950–1979, the first four modes of empirical orthogonal function analysis successfully captured temporal and spatial responses of the riverbed to natural and anthropogenic impacts. That is, the first mode explained the mean riverbed profile and temporal variation in riverbed sediment volume. The second through fourth spatial eigenfunctions reflected spatial variation in vertical adjustment rate for phases II, III and I, respectively. The corresponding temporal eigenfunctions explained the respective effects on the riverbed of SGM, of imbalance between sediment transport capacity and sediment supply, and of dredging activity.  相似文献   

15.
Major interactions between terrestrial and marine environments in the Kara Sea occur within the estuaries of the largest Siberian rivers, the Ob and Yenisei. Mesozooplankton community plays an important role in the transformation of allochthonous organic matter. All published data on zooplankton activity in the Ob Estuary have been obtained for the period of decreased river discharge. The aim of our study was to assess zooplankton distribution and grazing under various hydrological regimes (high-low river discharge and varying wind direction) in order to better understand the mechanisms governing this process. The study was carried out along a quasi-latitudinal transect in the Ob Estuary at the beginning of August (high discharge) and end of September 2010 (decreased discharge) and end of August 2014 (high discharge and onshore winds). Zooplankton grazing was assessed with the gut fluorescent approach. Under high river discharge, zooplankton biomass was low (mean 98 mg wet weight m?3), peaks of species abundance were spatially separated, and grazing did not exceed 2% of phytoplankton biomass. Weakening river discharge at the end of September led to the formation of hydrographic fronts, and zooplankton biomass was an order of magnitude higher (mean value 947 mg wet weight m?3) with dense local aggregations with biomass reaching 3600 mg wet weight m?3. These aggregations formed a pelagic “biofilter” grazing up to 26% of phytoplankton biomass per day. The peaks of abundance of the majority of species coincided at the pronounced hydrographic front forming dense local aggregations with biomass reaching 3600 mg wet weight m?3. These aggregations formed a pelagic biofilter utilizing daily up to 26% of phytoplankton biomass.  相似文献   

16.
为全面描述黄河口尾闾段的河床形态调整及过流能力变化,采用河段平均的计算方法,确定了尾闾段(利津—西河口)1990—2016年汛后断面及河段尺度的平滩特征参数,分析河段平滩河槽形态调整特点、河段平滩流量变化过程及其与累积河床冲淤量的关系。结果表明:近30年来黄河尾闾段的河床形态调整过程较为复杂,河相系数在1990—2003年呈振荡式升高,2003年以后持续减小,说明断面形态朝窄深方向发展;平滩流量变化与河段冲淤过程密切相关,淤积时平滩流量减小,反之则增大;建立这些河段平滩特征参数与利津站前4年汛期平均水流冲刷强度的幂函数关系,且相关系数均大于0.8,说明黄河口尾闾段河床形态调整及过流能力变化能较好地响应利津站水沙条件的改变。  相似文献   

17.
Stony Creek (drainage area 1920 km2), a tributary to the Sacramento River 200 km north of San Francisco, has experienced channel adjustments to both dam construction and instream gravel extraction. Black Butte Dam, constructed in 1963, reduced flood peaks and trapped the annual 100,000 m3 of bedload sediment formerly delivered from the upper watershed. The reach below the dam changed from an active braided channel to an incised, single-thread channel shortly after dam construction. About 25 km downstream of the dam, large instream gravel mines annually extract 230,000–580,000 m{su3} and have induced channel incision of over 5 m, necessitating bridge repairs costing US$1.4 million.  相似文献   

18.
《Applied Geochemistry》2003,18(2):221-239
The Aznalcóllar tailings dam at Boliden Apirsa's Aznalcóllar/Los Frailes Ag–Cu–Pb–Zn mine 45 km west of Seville, Spain, was breached on 25 April 1998, flooding approximately 4600 hectares of land along the Rı́os Agrio and Guadiamar with approximately 5.5 million m3 of acidic water and 1.3×106 m3 of heavy metal-bearing tailings. Most of the deposited tailings and approximately 4.7×106 m3 of contaminated soils were removed to the Aznalcóllar open pit during clean-up work undertaken immediately after the spill until January 1999. Detailed geomorphological and geochemical surveys of the post-clean-up channel, floodplain and valley floor, and sediment and water sampling, were carried out in January and May 1999 at 6 reaches representative of the types of river channel and floodplain environments in the Rı́o Guadiamar catchment affected by the spill. The collected data show that the clean-up operations removed enough spill-deposited sediment to achieve pre-spill metal (Ag, As, Cd, Cu, Pb, Sb, Tl, Zn) concentrations in surface sediment. These concentrations, however, are still elevated above pre-mining concentrations, and emphasise that mining continues to contaminate the Agrio-Guadiamar river system. Dilution by relatively uncontaminated sediment appears to reduce metal concentrations downstream but increases in metal and As concentrations occur downstream, presumably as a result of factors such as sewage and agriculture. River water samples collected in May 1999 have significantly greater dissolved concentrations of metals and As than those from January 1999, probably due to greater sulphide oxidation from residual tailings with concomitant release of metals in the warmer early summer months. These concentrations are reduced downstream, probably by a combination of dilution and removal of metals by mineral precipitation. Single chemical extractions (de-ionised water, CaCl2 0.01 mol l−1, CH3COONH4 1 M, CH3COONa 1 M and ammonium oxalate 0.2 M) on alluvial samples from reaches 1 and 6, the tailings, pre-spill alluvium and marl have shown that the order of sediment-borne contaminant mobility is generally Zn>Cd>Cu>Pb>As. Pb and As are relatively immobile except possibly under reducing conditions. Much of the highly contaminated sediment remaining in the floodplain and channel still contains a large proportion of tailings-related sulphide minerals which are potentially reactive and may continue to release contaminants to the Agrio–Guadiamar river system. Our work emphasises the need for pre-mining geomorphological and geochemical data, and an assessment of potential contributions of contaminants to river systems from other, non-mining sources.  相似文献   

19.
Groundwater can play an important role in the compensation of runoff reduction due to extreme climate events such as droughts, as well as in response to anthropogenic actions such as the construction of a dam. The increase in 226Ra specific activity and the runoff from September to December in 2006 is used to estimate the total discharge of groundwater along the mid-lower reaches of the Changjiang River. The total groundwater discharge was found to account for 31% of the increased discharge between Yichang and Datong. The groundwater discharge to lakes (i.e. Dongting Lake) constituted the major contribution of groundwater discharge to the mid-lower reaches of the Changjiang River. More importantly, the second impounding operation of the Three Gorges Dam from 20 September to 27 October 2006 induced a water level decrease in surrounding lakes and rivers, which led to an additional groundwater discharge of 63.3?×?108?m3, accounting for 85% of the total groundwater discharge in the same period. Taken together, these observations indicate that groundwater discharge along the mid-lower reaches plays an important role in maintaining stream flow in the drought season, especially in extreme drought years or in response to human activities.  相似文献   

20.
The failure of a lava dam 165,000 yr ago produced the largest known flood on the Colorado River in Grand Canyon. The Hyaloclastite Dam was up to 366 m high, and geochemical evidence linked this structure to outburst-flood deposits that occurred for 32 km downstream. Using the Hyaloclastite outburst-flood deposits as paleostage indicators, we used dam-failure and unsteady flow modeling to estimate a peak discharge and flow hydrograph. Failure of the Hyaloclastite Dam released a maximum 11 × 109 m3 of water in 31 h. Peak discharges, estimated from uncertainty in channel geometry, dam height, and hydraulic characteristics, ranged from 2.3 to 5.3 × 105 m3 s−1 for the Hyaloclastite outburst flood. This discharge is an order of magnitude greater than the largest known discharge on the Colorado River (1.4 × 104 m3 s−1) and the largest peak discharge resulting from failure of a constructed dam in the USA (6.5 × 104 m3 s−1). Moreover, the Hyaloclastite outburst flood is the oldest documented Quaternary flood and one of the largest to have occurred in the continental USA. The peak discharge for this flood ranks in the top 30 floods (>105 m3 s−1) known worldwide and in the top ten largest floods in North America.  相似文献   

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