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1.
In volcanic areas of Idaho, Oregon and Montana, a number of perennial streams emerge from single springs or zones of springs. Surface drainage areas to these springs can be very small, often much smaller than the recharge area of the springs. Channels downstream of springs are often straight, or if sinuous, without regularity to the pattern. Bars are absent or poorly defined, but islands or downed timber are common in the channel. Channel width-to-depth ratios are large relative to those of runoff-dominated channels. Downstream hydraulic geometry exponents are similar, but the exponents for width and velocity are greater in spring-dominated channels. Manning roughness values are relatively large. The bedsurface in gravel-bed spring-dominated streams is armored. Computations indicate that bed material is probably capable of moving at bankfull stage.The hydrograph of spring-dominated streams is damped as compared to runoff-dominated streams locally and elsewhere. Peak flows occur months after precipitation or snowmelt. Mean annual flow for spring-dominated streams averages 72% of the flood with a recurrence interval of 2 years; the mean annual flow for runoff-dominated channels averages 18% locally and 25% elsewhere. The 50-year flood averages 1.6 times the 2-year flood on the annual series while the corresponding value for runoff-dominated channels in the region is 2.5. The damped hydrograph of spring-dominated streams suggests that they are somewhat different from runoff-dominated channels in the relationship between water and sediment. In spring-dominated channels, 34% of sediment is transported by flows above the 2-year flood—less than is observed typically in runoff-dominated channels. The effective discharge is similar in magnitude to the 2-year flood.  相似文献   

2.
Geometric, hydraulic, and sediment characteristics in arid badlands near Borrego Springs, California, are examined in relation to precipitation events of varying magnitude and frequency. The longitudinal and cross profiles of five ephemeral channels occupying a 2.5 km2 catchment were surveyed under pre-and post-storm conditions during the February 1976-December 1978 period. Such arid region channels offer the opportunity to observe and explain rates and methods of profile change under different flow types in a short period of time. Catchment responses to light winter events include substantial lags between initial precipitation and channel runoff, the limited downstream movement of small slugs of sediment, high losses of discharge into channel alluvium, and prolonged mass movement of debris from adjacent hillslopes into the channels following the storm events thus promoting aggradation along certain channel reaches. Responses to intense summer storms include explosive channel and hillslope runoff and localized scour and fill, both during and following such events, thereby promoting substantial aggradation and erosion along portions of the channels. Although ephemeral flow conditions may produce channel profiles which are distinct from those in perennial streams, the evaluation of the methods of sediment transport and the storage of debris in arid catchments offer useful explanation for other environments.  相似文献   

3.
Slope–channel coupling and in-channel sediment storage can be important factors that influence sediment delivery through catchments. Sediment budgets offer an appropriate means to assess the role of these factors by quantifying the various components in the catchment sediment transfer system. In this study a fine (< 63 µm) sediment budget was developed for a 1.64-km2 gullied upland catchment in southeastern Australia. A process-based approach was adopted that involved detailed monitoring of hillslope and bank erosion, channel change, and suspended sediment output in conjunction with USLE-based hillslope erosion estimation and sediment source tracing using 137Cs and 210Pbex. The sediment budget developed from these datasets indicated channel banks accounted for an estimated 80% of total sediment inputs. Valley floor and in-channel sediment storage accounted for 53% of inputs, with the remaining 47% being discharged from the catchment outlet. Estimated hillslope sediment input to channels was low (5.7 t) for the study period compared to channel bank input (41.6 t). However an estimated 56% of eroded hillslope sediment reached channels, suggesting a greater level of coupling between the two subsystems than was apparent from comparison of sediment source inputs. Evidently the interpretation of variability in catchment sediment yield is largely dependent on the dynamics of sediment supply and storage in channels in response to patterns of rainfall and discharge. This was reflected in the sediment delivery ratios (SDR) for individual measurement intervals, which ranged from 1 to 153%. Bank sediment supply during low rainfall periods was reduced but ongoing from subaerial processes delivering sediment to channels, resulting in net accumulation on the channel bed with insufficient flow to transport this material to the catchment outlet. Following the higher flow period in spring of the first year of monitoring, the sediment supplied to channels during this interval was removed as well as an estimated 72% of the sediment accumulated on the channel bed since the start of the study period. Given the seasonal and drought-dependent variability in storage and delivery, the period of monitoring may have an important influence on the overall SDR. On the basis of these findings, this study highlights the potential importance of sediment dynamics in channels for determining contemporary sediment yields from small gullied upland catchments in southeastern Australia.  相似文献   

4.
黄河沙漠宽谷段水沙变化特征及驱动因素   总被引：1，自引：1，他引：0  
根据定位观测、第一次全国水利普查、遥感影像解译的数据,利用MWP、双累计曲线、水土保持分析法、数学模拟等方法,分析了黄河上游水沙变化特征,评估了多元驱动因素对2000-2012年黄河下河沿-头道拐沙漠宽谷段水沙变化的贡献率。结果表明:与20世纪70年代以前的基准期相比,2000年以来径流量、输沙量同步减少,水沙关系也发生变化,单位径流量的输沙量明显减少;沙漠宽谷段径流量减幅沿程不断增加而输沙量减幅沿程变化不大,水沙年内分配较基准期发生倒置,来沙系数不断减小;灌区引水引沙、水土保持措施、水库拦沙、支流来水来沙、水库调蓄及河道冲淤是沙漠宽谷段水沙变化的主要影响因子;经济社会发展用水对沙漠宽谷段径流量减少的作用最大,贡献率为81%,其次是水库蓄泄量,占15%以上;水库拦沙对头道拐输沙量减少的贡献率最大,占41%,其次是支流水土保持措施,贡献率约占13%,入黄风沙减少的贡献率并不大,约为6%,而河道淤积量、灌区引沙量较基准期都是减少的,贡献率分别约为-41%和-8%;近10多年来降雨等自然因素对水沙变化的作用相对不大,起主要作用的是水库运用、水土保持、经济社会发展等人类活动因素。  相似文献   

5.
黄河内蒙河段河床冲淤演变特征及原因   总被引：4，自引：0，他引：4  
利用黄河内蒙段1962-2000年间4期大断面观测资料,计算了各期河床冲淤和河槽形态指标。发现从1962-2000年间前20年、中间9年及后9年,内蒙河段河槽500m2过水面积下河底高程发生了降低-升高-再升高的过程;河槽漫滩过水面积经历了升高-降低-再降低的过程,2000年只有1982年的大约一半;滩地经历了持续淤积过程,平均抬升0.25m;河槽宽深比值经历了变化不显著-增加-减小的过程。分析结果表明:气候变化、引水、水库拦沙和重点产沙支流来沙变化在河床冲淤和河床形态调整中作用较大;水库对径流的年内调节对1982年后河槽淤积贡献较大;来水来沙变化下河流多要素自动调整是造成河槽形态变化过程复杂的原因。  相似文献   

6.
We present data from a proglacial river in Iceland that exhibits very different sedimentological characteristics when compared to its alpine counterparts. The braidplain is characterised by coarse outburst gravels that inhibit sediment transport and channel change. Bedload transport is restricted to the movement of fine-grained gravels that pass through the channel system without promoting significant changes in channel geometry. Bar forms are erosional features, inherited from the last major peak flow, rather than depositional in nature. On the basis of our observations we conclude that braidplain morphology is controlled by low frequency, high magnitude flow events, possibly associated with glacial outburst floods. This is in marked contrast to process-form relationships in more dynamic alpine proglacial channels that are characterised by high rates of sediment transport and channel change.  相似文献   

7.
祖厉河流域位于年降水量200～400 mm之间过渡带,是气候变化最敏感和最为复杂的区域之一。运用祖厉河流域1955-2013年径流量、输沙量与年降雨量的变化趋势、时段特征进行了分析。结果表明：祖厉河流域降雨量、径流量和输沙量存在年际变化大、逐年减小的变化趋势;年降雨量在1995年出现突变点,降雨量存在明显的丰水和枯水变化,丰水时段（1955-1989年）年降水量为376.2 mm,枯水时段（1990-2013年）年降水量为224.9 mm;径流量和泥沙量的突变点分别出现在1995年和2000年;依据UFk值信度变化趋势,将径流量、输沙量变化分为非显著减少（1955-1971年）、显著减少（1972-1985年）、较显著减少（1986-2000年）和极显著减少（2001-2013年）四个时期。  相似文献   

8.
An avulsion of the lower Saskatchewan River in the 1870s inundated a large segment of peat-covered floodplain that subsequently has become aggraded with a broad (500 km2) belt of alluvium deposited by the redirected flow. Routing of water and sediment discharge through the avulsion-affected area has been accomplished mainly by networks of sandy bedded anastomosed channels that have formed, evolved, and abandoned as the alluvial belt prograded down the floodplain slope. These processes continue today, though at a much-reduced rate. New channels, formed by crevassing and basinward extension of distributaries, are initially small and shallow, with bottom elevations situated within the avulsive alluvium but above the pre-avulsion peat (floodplain) surface. Subsequent enlargement and downcutting of many of these channels eventually uncovers the underlying peat layer whose resistance to erosion exerts significant influence on cross-sectional shape and further channel development. Peat-floored channels tend to have rectangular cross-sections, high ratios of average to maximum depth (D/Dmax), and a large range of width-to-depth ratios. If the channel continues to enlarge, the peat layer eventually becomes breached, commonly leading to temporarily irregular cross-sections caused by localized scouring at the breach sites. Eventually, the peat layer is completely eroded from the channel floor by undercutting and slumping, after which channel shape becomes governed mainly by other perimeter characteristics. Channels unaffected by peat, either before the peat layer is encountered during early channel development or after it is entirely removed, tend to have low width/depth ratios and a large range of D/Dmax values.  相似文献   

9.
We have monitored initiation conditions for six debris flows between May 2004 and July 2006 in a 0.3 km2 drainage basin at Chalk Cliffs; a band of hydrothermally-altered quartz monzonite in central Colorado. Debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14° to 45°. The availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes. Rainfall exceeding I = 6.61(D)− 0.77, where I is rainfall intensity (mm/h), and D is duration (h), was required for the initiation of debris flows in the drainage basin. The approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0.15 m3/s. Colluvium in the basin was unsaturated immediately prior to (antecedent) and during debris flows. Antecedent, volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4–9%, and 4–7%, respectively. During debris flows, peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10–20%, and 4–12%, respectively. Channel sediment at a depth of 45 cm was unsaturated before and during debris flows; antecedent moisture ranged from 20–22%, and peak moisture ranged from 24–38%. Although we have no measurements from shallow rill or channel sediment, we infer that it was unsaturated before debris flows, and saturated by surface-water runoff during debris flows.Our results allow us to make the following general statements with regard to debris flows generated by runoff in semi-arid to arid mountainous regions: 1) high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff, 2) locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows, and 3) rainfall and simulated surface-water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment.  相似文献   

10.
Douglas M. Thompson   《Geomorphology》2008,99(1-4):420-432
A coarse surface layer can help to limit bedload transport rates in channels with cobble and gravel beds. In these systems, periodic boulder-sized clasts often exist with small deposits of fine material in the lee of these large bed elements. A combined field and flume study was conducted to investigate the potential impact of lee deposits with distinctly finer sediment-sizes behind boulders on bedload transport rates. Detailed sediment characterizations were performed on surface, subsurface, and lee sediments in two coarse-bedded Connecticut channels. Bedload measurements also were conducted in a series of flows that approached the bankfull level in these two systems to determine transport rates and the size distribution of bedload material. A 6-m long, 0.5-m wide flume was used to model these systems with fine sediment passing over a fixed bed of sediment particles with uniform-sized, large bed elements. Sediment distributions of the lee deposits in the two Connecticut channels indicate that lee deposits may be produced from winnowing of sediments from the surface layer. Lee deposits also exhibit sediment distributions similar to bedload sediment distributions from low to near-bankfull flow in one of the two channels. Bedload sediments in the second channel were finer than lee deposits, presumably from selective entrainment of fines. Flume experiments demonstrate that bedload transport rates are lower for periods of steady flow relative to periods that include either an increase or decrease in discharge. The results show that lee sediments establish a metastable deposit behind each obstruction for a given discharge. Either increases or decreases in discharge disrupt this temporary stability and increase sediment delivery to the main flow. The study suggests that the influence of the rate of change in discharge may be as important as the absolute magnitude of discharge on sediment transport rates at moderate and low discharges in sediment-limited systems with large bed elements.  相似文献   

11.
This research evaluates the impact of rural-to-urban land use conversion on channel morphology and riparian vegetation for three streams in the Central Redbed Plains geomorphic province (central Great Plains ecoregion) of Oklahoma. The Deep Fork Creek watershed is largely urbanized; the Skeleton Creek watershed is largely rural; and the Stillwater Creek watershed is experiencing a rapid transition from rural to urban land cover. Each channel was divided into reaches based on tributary junctions, sinuosity, and slope. Field surveys were conducted at transects in a total of 90 reaches, including measurements of channel units, channel cross-section at bankfull stage, and riparian vegetation. Historical aerial photographs were available for only Stillwater Creek watershed, which were used to document land cover in this watershed, especially changes in the extent of urban areas (impervious cover).The three streams have very low gradients (< 0.001), width-to-depth ratios < 10, and cohesive channel banks, but have incised into red Permian shales and sandstone. The riparian vegetation is dominated by cottonwoods, ash, and elm trees that provide a dense root mat on stream banks where the riparian vegetation is intact. Channels increased in width and depth in the downstream direction as is normally expected, but the substrate materials and channel units remained unchanged. Statistical analyses demonstrated that urbanization did not explain spatial patterns of changes in any variables. These three channels in the central Redbed Plains are responding as flumes during peak flows, funneling runoff and the wash-load sediment downstream in major runoff events without any effect on channel dimensions. Therefore, local geological conditions (similar bedrock, cohesive substrates and similar riparian vegetation) are mitigating the effects of urbanization.  相似文献   

12.
The Lamar River watershed of northeastern Yellowstone contains some of the most diverse and important habitat in the national park. Broad glacial valley floors feature grassland winter range for ungulates, riparian vegetation that provides food and cover for a variety of species, and alluvial channels that are requisite habitat for native fish. Rapid Neogene uplift and Quaternary climatic change have created a dynamic modern environment in which catastrophic processes exert a major influence on riverine–riparian ecosystems. Uplift and glacial erosion have generated high local relief and extensive cliffs of friable volcaniclastic bedrock. As a result, steep tributary basins produce voluminous runoff and sediment during intense precipitation and rapid snowmelt. Recent major floods on trunk streams deposited extensive overbank gravels that replaced loamy soils on flood plains and allowed conifers to colonize valley-floor meadows. Tree-ring dating identifies major floods in 1918, ca. 1873, and possibly ca. 1790. In 1996 and 1997, discharge during snowmelt runoff on Soda Butte Creek approached the 100-year flood estimated by regional techniques, with substantial local bank erosion and channel widening. Indirect estimates show that peak discharges in 1918 were approximately three times greater than in 1996, with similar duration and much greater flood plain impact. Nonetheless, 1918 peak discharge reconstructions fall well within the range of maximum recorded discharges in relation to basin area in the upper Yellowstone region. The 1873 and 1918 floods produced lasting impacts on the channel form and flood plain of Soda Butte Creek. Channels may still be locally enlarged from flood erosion, and net downcutting has occurred in some reaches, leaving the pre-1790 flood plain abandoned as a terrace. Gravelly overbank deposits raise flood-plain surfaces above levels of frequent inundation and are well drained, therefore flood-plain soils are drier. Noncohesive gravels also reduce bank stability and may have persistent effects on channel form. Overall, floods are part of a suite of catastrophic geomorphic processes that exert a very strong influence on landscape patterns and valley-floor ecosystems in northeastern Yellowstone.  相似文献   

13.
黄河下游河床萎缩典型地表现为平滩水位下河床断面面积的趋势性减小,本文根据黄河下游实测断面和水沙资料采用相关分析方法研究了游荡段河床萎缩的主要影响因素。1960~1997年游荡段河床平滩水位下断面面积经历了1960~1964年和1974~1985年的扩张时期及1965~1973年和1986~1997年的萎缩时期,这种变化是多种因素共同作用的结果。在来水来沙中,年径流量是主要因素,洪峰流量和年平均含沙量是较次要的因素;本文所讨论的其它4个因素中,花园口以上引水量影响最大,降雨量影响次之,兰州以上水库的调节作用对河床断面面积的变化也有较明显的影响;三门峡水库三种不同的使用方式对下游河床有不同的影响,采取"蓄清排浊"方式后对下游河床的影响较小。  相似文献   

14.
The hydrodynamics of rivers approaching a receiving basin are influenced by the onset of backwater conditions that give rise to decelerating reach-average flow velocity and decreasing boundary shear stress. These changes occur across a spatial gradient over which decreasing sediment transport capacity triggers morphodynamic responses that include sediment deposition at the transition from uniform to nonuniform flow. As a consequence, the channel width-to-depth ratio and bed sediment grain size decrease downstream. While nonuniform flow and associated morphodynamic adjustments have been investigated in modern fluvial–deltaic systems, the impacts to fluvial–deltaic stratigraphy remain relatively unexplored. This represents an important unresolved gap: there are few contributions that link morphodynamic response to nonuniform flow, impacts on sediment deposition and influence on the rock record. This study uses a numerical model to explore how variable channel hydraulics influence long-term (1000s years) patterns of sediment deposition and development of stratigraphy. The model results indicate that: (a) nonuniform flow propagates upstream beyond the backwater transition that is traditionally estimated with a basic backwater length scale relationship. (b) Base-level fluctuations, especially rising, enhance the impact of nonuniform flow. (c) Sediment deposition shows large spatio-temporal variability, which ultimately contributes to unique stacking patterns of fluvial–deltaic stratigraphy. (d) Nonuniform flow imparts spatial variation in flow depth, channel bed slope and sediment grain size over the delta, and these signatures are potentially preserved and recognizable in the rock record.  相似文献   

15.
师长兴 《地理科学》2000,20(5):416-421
研究黄河和滹沱河对季节河化的适应性调整，发现季节化程度较高的滹沱河下游河床断面和平面形态调整幅度不大，而河床的糙率成倍增加造成下游的小水大灾现象；黄河下游近年流量减小，不断断流，主槽淤积，虽然河槽断面形态在游荡段变得更窄深，但主槽明显变小、变窄、变高，构成下游近年出现的小水大灾现象的主要原因。  相似文献   

16.
A quantitative assessment is made of suspended sediment load, including particulate organic matter and organic carbon, in 2014 for the small streams of the Northern Yenisei region, in the taiga–tundra transition zone (near the city of Igarka, Krasnoyarsk krai). It was found that the suspended sediment concentration (SSC) of the streams under investigation fluctuated between 2 and 18 mg/L during the summer–autumn low-water period of 2014. The proportion of dissolved organic matter (DOM) in the total sediment yield varied from 16.4% to 74.1%, depending on landscape-geomorphological conditions for suspended sediment formation: it is higher for streams with tundra catchments and lower on forest watersheds underlain by sandy and clayey loams. The DOM content varies from catchment to catchment from 1.63 to 2.42 mg/L, and the mean concentration of dissolved organic carbon (DOC) is estimated at 0.73 to 1.09 mg C/L. It is shown that the local channel transformations serve as the main source of POM and DOC input to the water of two out of three streams under study. Surface runoff or fast subsurface flow in the organic soil horizon is the external source of DOM input to the water of the third stream during flooding. Regional empirical dependencies were obtained, which correlate the water discharge, total SSC and the proportion of DOM are obtained. The long-term proportion of DOM in the annual suspended sediment flow of the Graviika river makes up 25% and DOC, 11%, or, in absolute values, 406 and 183 t/year, and in units of layer 1.26 and 0.57 t/km2, respectively.  相似文献   

17.
陈小红 《热带地理》2000,20(1):22-26
通过对６０年代和９０年代珠江三角洲河网典型汊河泥沙分配变化的对比分析,认为（１）珠江河口区的泥沙主要来自陆相径流挟带的下行泥沙和随潮流挟带的上溯泥沙,其中径流及其挟带的泥沙是现代珠江三角洲建造过程中的基本动力和物质,起着主导作用,而珠江河口区由径流挟带的悬移质泥沙又主要来自西江。（２）西北江干沙处于逐年淤积的总趋势,其中河流段冲淤变化不大,过渡段有冲有淤,以淤为主,潮流段由是普遍淤积。（４）海平面  相似文献   

18.
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19.
基于小波多尺度变换的渭河水沙演变规律研究   总被引：1，自引：0，他引：1  
关中平原地区是推动陕西省经济社会发展的引擎,其生产总值占陕西省的70%以上,但是水资源短缺、时空分布不均、河流含沙量高等问题严重制约其经济社会的发展。运用小波变换、滑动t检验、累积距平以及Yamamoto、Mann-Kendall等方法系统分析了1935-2011年渭河水沙序列演变规律。研究结果显示：77 a间除20世纪70年代、80年代外,其它年代渭河华县站水沙变化波动下降的匹配趋势均一致,其中径流量减流速度大于输沙量减沙速度;渭河水沙序列周期变化不一,径流量变化的主周期依次为38 a、14 a、4 a,输沙量变化的主周期依次为15 a、49 a、43 a、4 a;除输沙量49 a变化周期外,其他水沙变化周期大致相近;由于渭河输沙量变化所受气候及人类活动的影响远较径流量复杂,加之水沙异源,所以渭河华县站输沙量周期变化及突变点分布情况比径流量变化复杂,且其第一主周期变化呈现独特的变化态势。  相似文献   

20.
黄河内蒙古段洪峰特征及水沙关系变化   总被引：1，自引：0，他引：1  
本文通过黄河头道拐站1950-2009 年水沙年系列进行突变点分析, 识别出1969 年、1986 年、1996 年3 个突变点, 将黄河内蒙古段水文过程划分为4 个时期。在此基础上, 利用内蒙古段6 个水文站长系列日流量、日含沙量及泥沙组成数据, 划分了各站的夏汛洪峰, 并统计分析了分期洪峰的水沙分布特征和洪峰水沙关系, 揭示出夏汛洪峰流量和输沙率逐渐减少的规律:1996-2006 年与1954-1968 年相比, 夏汛洪峰水沙量占全年水沙的比例都减少了约一半, 流量级频率与输沙率乘积的峰值对应的流量也降低了约一半。分析认为, 黄河内蒙古段夏汛洪峰特征阶段性变化既有大型水库的影响, 又有气候变化及人类活动的影响, 而且后者的作用越来越大。分析发现, 20 世纪90 年代以前, 黄河上游水沙变化只是改变了内蒙古段来沙中粗颗粒泥沙的水沙关系, 显示出大流量输送粗颗粒泥沙能力相对增强的趋向;进入内蒙段后, 通过泥沙冲淤调整, 分粒径组泥沙水沙关系变化比较复杂。近期在水沙条件巨大变化下, 河流的输沙特性并没有发生根本变化, 但是无论全沙还是分组沙, 水沙关系曲线变陡, 大流量输送泥沙能力相对增强。  相似文献   

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