River flow mass exponents with fractal channel networks and rainfall

An important problem in hydrologic science is understanding how river flow is influenced by rainfall properties and drainage basin characteristics. In this paper we consider one approach, the use of mass exponents, in examining the relation of river flow to rainfall and the channel network, which provides the primary conduit for transport of water to the outlet in a large basin. Mass exponents, which characterize the power-law behavior of moments as a function of scale, are ideally suited for defining scaling behavior of processes that exhibit a high degree of variability or intermittency. The main result in this paper is an expression relating the mass exponent of flow resulting from an instantaneous burst of rainfall to the mass exponents of spatial rainfall and that of the network width function. Spatial rainfall is modeled as a random multiplicative cascade and the channel network as a recursive replacement tree; these fractal models reproduce certain types of self-similar behavior seen in actual rainfall and networks. It is shown that under these modeling assumptions the scaling behavior of flow mirrors that of rainfall if rainfall is highly variable in space, and on the other hand flow mirrors the structure of the network if rainfall is not so highly variable.     

CHANNEL EROSION DAMAGES AND PROTECTION MEASURES IN SOUTHEAST ARIZONA

1INTRODUCTIONThesouthwesternregionoftheUnitedStates,includingSoutheastArizona,ischaracterizedbyasemiaridclimatewithhotsummers,mildwinters,andephemeralstreamsdrainingsparselyvegetatedareas.ChannelmorphologyoftheephemeralstreamsinSoutheastArizonaisinfluencedbybothlateralandverticalchannelchangesoccurringduringmajorfloods.Lateralchannelchangesoccurinthreewaysbankerosion,meandermigration,andchannelavulsion.Verticalchannelchangesinclude,beddegradationoraggradation,andmayoccurseparatelyorinco…     

STABILITY OF NIANCHU RIVER AFTER REGULATION BY STRAIGHTENING: A CASE STUDY FROM TIBET, CHINA

IINTRODUCTIONTheNianchuRiverCatchmentisoneofthemaingrainproducingareasofTibet.TheengineeringregulationoftheriverisanimportantcomponentofstatekeyprojectofChina,"OneRiverandTwoTributariesProject"."OneRiver"herestandsfortheYarlungZhangboRiverandthe"TwoTributaries"aretheNianchuRiverandtheLasaRiverinCentral-SouthernTibet.InordertoimprovethewaterresourcesandtopreventfloodinginTibet,aseriesofhydropowerstations,irrigationdiversionprojects,floodcontrollevees,andreforestationprogramshaveb…     

Channel geometry of mountain streams in New Zealand

A dataset of 21 study reaches in the Porter and Kowai rivers (eastern side of the South Island), and 13 study reaches in Camp Creek and adjacent catchments (western side of the South Island) was used to examine downstream hydraulic geometry of mountain streams in New Zealand. Streams in the eastern and western regions both exhibit well-developed downstream hydraulic geometry, as indicated by strong correlations between channel top width, bankfull depth, mean velocity, and bankfull discharge. Exponents for the hydraulic geometry relations are similar to average values for rivers worldwide. Factors such as colluvial sediment input to the channels, colluvial processes along the channels, tectonic uplift, and discontinuous bedrock exposure along the channels might be expected to complicate adjustment of channel geometry to downstream increases in discharge. The presence of well-developed downstream hydraulic geometry relations despite these complicating factors is interpreted to indicate that the ratio of hydraulic driving forces to substrate resisting forces is sufficiently large to permit channel adjustment to relatively frequent discharges.     

Simulating bed evolution following the Barlin Dam (Taiwan,China) failure with implications for sediment dynamics modeling of dam removal

The failure of the Barlin Dam in Taiwan, China offers an important case study for evaluating concepts in modeling the rapid erosion and channel recovery following intentional and unplanned dam removals. We present a modeling effort that applied a 1D and quasi-2D uncoupled hydraulics and sediment model (NETSTARS) to evaluate how discretization and parameterization influence thefitofbed elevationpredic-tions to observations following dam failure. Our analysis evaluated the model sensitivity to sediment transport function, active layer thickness, and number of stream tubes used to define the cross-section. Results indicate that a) the model is more sensitive to active layer thickness and sediment transport function than to the number of stream tubes, b) development of dam removal models are likely to benefit from varying the active layer thickness in time, and c) increased lateral discretization does not appear to improve model fit in the steep and rapidly changing river environment at our site. We conclude with discussion on differences between, identifying the need for, and general use of 1D, quasi-2D, and fully 2D models in dam removal and failure analysis.     

Quantitative assessment of dissolved radiotracers in the English Channel: Sources, average impact of la Hague reprocessing plant and conservative behaviour (1983, 1986, 1988, 1994)

Knowledge of long-term movements of water-masses in the English Channel has been substantially improved using hydrodynamic modelling coupled with radio-tracers studies; nevertheless, the precision of results so obtained is still largely dependent on measurement precision. New tools are now available to make more accurate determinations of radio-tracer distribution: (1) Repositioning of station locations at the same tide reference-time, giving a homogeneous spatial data set, coupled with the possibility of interpolating and quantifying the amounts of dissolved radioactivity flowing through the English Channel; (2) the first measurements of tritium (³H) in seawater on a large scale in the English Channel demonstrate that this fully conservative radionuclide is a clearly identifiable marker of industrial releases; (3) recent campaigns carried out during the FLUXMANCHE II CCE (1994) programme show the general distribution of dissolved radionuclides ¹³⁷Cs, ¹³⁴Cs, ⁶⁰Co, ¹²⁵Sb, ¹⁰⁶Ru and ³H in the English Channel and the Irish Sea; and (4) the re-utilisation of data from previous campaigns (1983, 1986, 1988) provides indications, at any given location in the English Channel, about the average dilution and distribution of releases derived from the La Hague reprocessing plant. Excesses and losses of radionuclides are now quantified with respect to known source terms; estimates of losses are provided for non-conservative radionuclides, while an excess of ¹³⁷Cs was observed in the English Channel during the period 1983–1994. This excess, which has the same order of magnitude as the quantities released from La Hague plant in the English Channel, could be explained by about 1% of the Sellafield reprocessing plant releases entering the Channel. These results confirm and give a more detailed picture of the previously known distribution of water masses in the English Channel. They lead to clear information about transit times and dilution at this scale, and provide directly comparable data for the validation of hydrodynamic models.     

阜新矿震台网无线信道测试

为了提高矿震台网的运行率,保障地震数据的连续率、完整率,对阜新矿震台网的信道进行了测试,主要包括制作传播路径地形剖面图以了解信道传输的视通条件、对信道传播损耗的理论计算及功率储备的测量、进行接收场强及背景干扰的测试以确定传输频点。结果显示,阜新矿震台网无线传输信道的场强在50~73 dB之间,能够保证无线信号传输质量,符合遥测台网建设技术规范要求。     

The influence of organic debris on channel morphology and bedload transport in a New Zealand forest stream

The behaviour and form of, and bedload sediment transport through, a 3.5 m wide forest stream have been monitored for nearly three years. Bedload transport is highly episodic and spatially variable, and is controlled less by water discharge than by sediment availability. Organic debris in the channel creates temporary base levels and sites at which coarse sediment may remain stored for long periods; collapse or disruption of log and debris jams makes sediment available for transport in only a small proportion of the runoff events that are actually competent to move the material. Even then, sediment travels only a short distance before being redeposited, frequently behind debris accumulations further downstream. Rates of sediment transport during a given runoff event can vary markedly over short distances along the stream, again depending on whether sediment was made available for transport by log jam collapse upstream. Organic debris is therefore a major constraint on the application of physical laws and theories to explaining sediment movement in, and the morphology of, this stream.     

CHANNEL SHRINKAGE AND ITS INSTABILITY IN THE LOWER YELLOW RIVER1

From the mid 1980s through the late 1990s, the channel of the lower Yellow River experienced serious shrinkage, which has decreased the flood conveyance of the channel and the sediment carrying capacity of the flow, raised the water levels of floods, and, thus, severely threatened the safety of flood control along the river. The completion of Xiaolangdi Dam in 1999 could help mitigate the channel shrinkage problem, but the situation has not changed yet. This paper analyses the characteristics, mechanisms, and conditions resulting in channel shrinkage, points out channel instabilities, and puts forward approaches of channel rehabilitation.     

Slope-induced changes in channel character along a gravel-bed stream: The Allt Dubhaig,Scotland

Changes in channel character along a small river in the Scottish Highlands are described using measurements in seven reaches over a 3 km length with no significant tributaries but a decline in slope from 0.02 to 0.00015 because of local baselevel control. This decline in slope is associated with rapid downstream fining of the gravel bed followed by an abrupt transition to a sand bed. The channel pattern alters progressively rather than abruptly, in the sequence (1) near-braided, (2) meandering with active point-bar chutes, (3) meandering with active outer-bank talweg, (4) stable equiwidth sinuous. The changes in channel pattern and hydraulic geometry are predicted better by rational approaches based on critical shear stress or other physical concepts than by purely empirical discriminant or trend equations. Measurements in five reaches confirm a downstream decrease in shear stress and the amount and calibre of bedload. It is argued that the downstream changes in channel character in this stream are induced by profile concavity inherited from deglacial conditions, are typical of many streams in mountainous areas and can be understood in terms of slope-induced changes in hydraulic properties.