DOCSLIB.ORG

Controls on Alluvial Fan Long-Profiles

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Controls on Alluvial Fan Long-Profiles Controls on alluvial fan long-profi les Jonathan D. Stock* Kevin M. Schmidt David M. Miller U.S. Geological Survey, 345 Middlefi eld Road, Menlo Park, California 94025, USA ABSTRACT these hypotheses for alluvial fan long-profi les Calculations that match observed fan long- using detailed hydraulic and particle-size profi les require an exponential decline in Water and debris fl ows exiting confi ned data in sediment transport models. On four gravel transport rate, so that on some fans valleys have a tendency to deposit sediment alluvial fans in the western U.S., we fi nd that approximately half of the load must be depos- on steep fans. On alluvial fans where water channel hydraulic radiiare largely 0.5–0.9 m ited off channel every ~0.20–1.4 km downfan. transport of gravel predominates, chan- at fan heads, decreasing to 0.1–0.2 m at distal This leads us to hypothesize that some allu- nel slopes tend to decrease downfan from margins. We fi nd that median gravel diam- vial fan long-profi les are statements about ~0.10–0.04 to ~0.01 across wide ranges of eter does not change systematically along the the rate of overbank deposition of coarse climate and tectonism. Some have argued upper 60%–80% of active fan channels as particles downfan, a process for which there that this pattern refl ects grain-size fi ning slope declines, so downstream gravel fi ning is currently no mechanistic theory. downfan such that higher threshold slopes cannot explain most of the observed channel are required just to entrain coarser parti- slope reduction. However, as slope declines, Keywords: alluvial fan, long-profi le, Mojave cles in the waters of the upper fan, whereas channel-bed sand cover increases systemati- Desert, sediment transport. lower slopes are required to entrain fi ner cally downfan from areal fractions of <20% grains downfan (threshold hypothesis). An above fan heads to distal fan values in excess INTRODUCTION older hypothesis is that slope is adjusted to of 70%. As a result, entrainment thresholds transport the supplied sediment load, which for bed material might decrease systemati- Sediment exiting confi ned valleys in debris decreases downfan as deposition occurs cally downfan, leading to lower slopes. How- fl ows or entrained in fl oods commonly spreads (transport hypothesis). We have begun to test ever, current models of this effect alone tend laterally, forming fans (e.g., Fig. 1). Where the to underpredict downfan slope changes. This proportion of sediment transported by water trac- *E-mail: [email protected] is likely due to off-channel gravel deposition. tion is substantial, these fans are commonly called A Globe, Providence Mts., CA Hanaupah, Death Valley, CA B Figure 1. Photographs of alluvial fans whose modern channels transport gravel by water fl ow over a similar range of slopes. (A) Globe fan drains a low-relief (~500-m) source terrain of the Providence Mountains, eastern Mojave Desert. There are no active faults mapped in this area, and channel gradients decrease from ~0.06 at the active fan-head (high- albedo) channel to ~0.01, where the fan joins a sand-bedded axial wash. (B) Hanaupah fan drains a high-relief (~3000-m) source terrain of the Panamint Mountains, Death Valley, California. An active fault occurs in the lower right (see also Fig. 4), and fan gradients decrease from ~0.07 to less than 0.01, where the fan joins Badwater Playa in the foreground. GSA Bulletin; May/June 2007; 120; no. 5/6; p. 619–640; doi: 10.1130/B26208.1; 23 fi gures; 4 tables. For permission to copy, contact [email protected] 619 © 2007 Geological Society of America Stock et al. alluvial, after Drew (1873). For alluvial fans with slope may vary down different azimuths (e.g., part, a statement about the rate of downfan bed- steep source catchments and traction-transported Hooke and Rohrer, 1977), but long-profi les are material deposition. Later fl ume experiments gravel, channel slopes commonly decrease from commonly concave up (e.g., Denny, 1965). (e.g., Ikeda and Iseya, 1988) have shown that ~0.04–0.10 at fan heads to 0.01 or less at fan bases Drew (1873) proposed the fi rst explanation for Drew’s hypothesis can be demonstrated in the (e.g., Fig. 2). It is widely observed that deposits this concavity. He hypothesized that deposition laboratory, where fl ume channel slope decreased become increasingly fi ne grained downfan, from reduced sediment supply progressively downfan. as gravel supply rate was reduced for a con- gravel-dominated proximal deposits, to sand- Consequently, the slope required to transport the stant discharge. But this hypothesis was never dominated distal deposits (e.g., Lawson, 1913; supply of sediment decreased downfan (e.g., tested on alluvial fans because subsequent work Eckis, 1928; Chawner, 1935). Average surface Fig. 3A). Concave-up long-profi les were, in focused on the control of slope by grain size 3000 Globe 2500 Sheep Creek Hanaupah Lucy Gray 2000 1500 elevation (m) 1000 Figure 2. (A) Channel long- profi les down most active axial thread of four intensively stud- ied fans and their source areas— 500 Globe, Sheep Creek, Hanaupah, and Lucy Gray. Data extracted CATCHMENT FAN from U.S. Geological Survey 0 A 7.5′ topographic maps, starting at valley head (see Stock and –10,000 0 10,000 20,000 Dietrich, 2003). Ticks indicate meters from fan head cross sections where we collected hydraulic geometry and grain 1 size; endpoints approximate fan Globe terminuses. (B) Slopes for each Sheep Creek long-profi le using every contour ′ Hanaupah on U.S. Geological Survey 7.5 topographic maps. We attempt 0.1 Lucy Gray to test whether this slope change is a statement about threshold sediment transport associated with downfan bed-material fi n- ing or sediment transport rates 0.01 that decline downfan. 7.5’ slope 0.001 CATCHMENT FAN B 0.0001 –10,000 0 10,000 20,000 meters from fan head 620 Geological Society of America Bulletin, May/June 2008 Alluvial fan long-profi les alone. Workers proposed that local slope is set by A the coarsest grain fraction that can be entrained 6 at a given reach (Fig. 3B); as this threshold grain size decreases downfan, fan slopes decline (e.g., Blissenbach, 1952, 1954; Bluck, 1964; Hooke, 4 1968; Kesel, 1985; Kesel and Lowe, 1987). In Slope (%) Ikeda and Iseya, 1988 one of the most commonly cited examples, Blis- senbach (1951, 1952, 1954) measured maximum ~ clast size at cut banks down dissected fans of the 2 qsed Santa Catalina Mountains, Arizona. He reported 0 0.5 1 a strong covariance between maximum clast size Bedload transport (g/cm/s) and local surface slope, an observation that has formed the basis for much subsequent work. This threshold hypothesis is widely accepted in the literature (McGowen, 1979; Nilsen, 1982; Ethridge, 1985; Miall, 1996) and has been used to model alluvial fans (Price, 1974). These alternate hypotheses for downfan slope Transport hypothesis: slope declines with lower fluxes reduction can be restated (Fig. 3) as transport versus threshold entrainment controls on fan long-profi les. However, it is not clear which expected relation B process dominates in the fi eld, because despite Shields’ criteria over one hundred years of fi eld work and model- Rc ing (summarized in Table 1; and by Bull, 1977; slope Nilsen, 1982; Blair and McPherson, 1994a, d50 begins to move 1994b), the literature does not contain suffi cient d /R hydraulic and grain-size data to test these alter- 50 nate hypotheses. Most studies (e.g., Eckis, 1928; Beaty, 1963; Bluck, 1964; Kesel, 1985; Kesel S and Lowe, 1987; Hubert and Filipov, 1989) char- c acterized grain size as the median or average of the coarsest ten grains within a given square or distance, sampling in straight lines downfan, potentially across deposits of different age and processes. This characterization creates two dif- fi culties in using the data. First, it is diffi cult to isolate the role of individual processes. Second, there is no theory for the effect of exceptional Threshold hypothesis: slope declines with grain size grain sizes (e.g., maximum clast size) on chan- nel reach slope. For instance, some fl ume stud- Figure 3. Conceptual model of factors that control alluvial-fan slope. Figure 3A illus- trates Drew’s 1873 hypothesis that declining transport rate q (decreasing arrows) ies (e.g., Solari and Parker, 2000) indicate that at sed slopes >0.02, the coarsest particles may be excep- downfan lead to slope reduction (long-profi le modifi ed from Drew, 1873). Inset graph tionally mobile because of strong drag forces. As modifi ed from Ikeda and Iseya (1988) illustrates this effect in a supercritical fl ume a result, the assumption underlying earlier stud- whose slopes approximate those found on many alluvial fans (e.g., Fig. 2B). Figure 3B ies that grain size controls slope cannot be tested illustrates later threshold hypothesis (e.g., Blissenbach, 1952) that declining grain size with available data. Although it is known from downfan (either because of shallowing fl ow, as shown, or because of comminution) photographs and fi eld inspection that the grain leads to a decrease in slope. Inset shows an illustration of this effect as characterized by Shields’ criterion (see Equation (1) in text), where particles of d diameter begin to size of many alluvial fans varies from gravel 50 move once fl ow reaches a depth of R at S slope. Smaller inset shows predicted rela- dominated to sand or fi ner fraction deposits at c c tion between channel slope and ratio of d to R for a threshold entrainment channel.
Load more

Recommended publications
  • Alluvial Fans in the Death Valley Region California and Nevada
    Alluvial Fans in the Death Valley Region California and Nevada GEOLOGICAL SURVEY PROFESSIONAL PAPER 466 Alluvial Fans in the Death Valley Region California and Nevada By CHARLES S. DENNY GEOLOGICAL SURVEY PROFESSIONAL PAPER 466 A survey and interpretation of some aspects of desert geomorphology UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library has cataloged this publications as follows: Denny, Charles Storrow, 1911- Alluvial fans in the Death Valley region, California and Nevada. Washington, U.S. Govt. Print. Off., 1964. iv, 61 p. illus., maps (5 fold. col. in pocket) diagrs., profiles, tables. 30 cm. (U.S. Geological Survey. Professional Paper 466) Bibliography: p. 59. 1. Physical geography California Death Valley region. 2. Physi­ cal geography Nevada Death Valley region. 3. Sedimentation and deposition. 4. Alluvium. I. Title. II. Title: Death Valley region. (Series) For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 CONTENTS Page Page Abstract.. _ ________________ 1 Shadow Mountain fan Continued Introduction. ______________ 2 Origin of the Shadow Mountain fan. 21 Method of study________ 2 Fan east of Alkali Flat- ___-__---.__-_- 25 Definitions and symbols. 6 Fans surrounding hills near Devils Hole_ 25 Geography _________________ 6 Bat Mountain fan___-____-___--___-__ 25 Shadow Mountain fan..______ 7 Fans east of Greenwater Range___ ______ 30 Geology.______________ 9 Fans in Greenwater Valley..-----_____. 32 Death Valley fans.__________--___-__- 32 Geomorpholo gy ______ 9 Characteristics of fans.._______-___-__- 38 Modern washes____.
    [Show full text]
  • Geomorphic Classification of Rivers
    9.36 Geomorphic Classification of Rivers JM Buffington, U.S. Forest Service, Boise, ID, USA DR Montgomery, University of Washington, Seattle, WA, USA Published by Elsevier Inc. 9.36.1 Introduction 730 9.36.2 Purpose of Classification 730 9.36.3 Types of Channel Classification 731 9.36.3.1 Stream Order 731 9.36.3.2 Process Domains 732 9.36.3.3 Channel Pattern 732 9.36.3.4 Channel–Floodplain Interactions 735 9.36.3.5 Bed Material and Mobility 737 9.36.3.6 Channel Units 739 9.36.3.7 Hierarchical Classifications 739 9.36.3.8 Statistical Classifications 745 9.36.4 Use and Compatibility of Channel Classifications 745 9.36.5 The Rise and Fall of Classifications: Why Are Some Channel Classifications More Used Than Others? 747 9.36.6 Future Needs and Directions 753 9.36.6.1 Standardization and Sample Size 753 9.36.6.2 Remote Sensing 754 9.36.7 Conclusion 755 Acknowledgements 756 References 756 Appendix 762 9.36.1 Introduction 9.36.2 Purpose of Classification Over the last several decades, environmental legislation and a A basic tenet in geomorphology is that ‘form implies process.’As growing awareness of historical human disturbance to rivers such, numerous geomorphic classifications have been de- worldwide (Schumm, 1977; Collins et al., 2003; Surian and veloped for landscapes (Davis, 1899), hillslopes (Varnes, 1958), Rinaldi, 2003; Nilsson et al., 2005; Chin, 2006; Walter and and rivers (Section 9.36.3). The form–process paradigm is a Merritts, 2008) have fostered unprecedented collaboration potentially powerful tool for conducting quantitative geo- among scientists, land managers, and stakeholders to better morphic investigations.
    [Show full text]
  • Fan-Deltas and Braid Deltas: Varieties of Coarse-Grained Deltas
    Fan-deltas and braid deltas: Varieties of coarse-grained deltas John g. Mcpherson \ ,,,.,„ , , GANAPATHY SHANMUGAM > Mob" Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 RICHARD J. MOIOLA J Dallas, Texas 75381 ABSTRACT delta sediments; they lack a muddy matrix; ening of the definition of fan-delta to the point of they display size grading and bar migration; confusion over its meaning and sedimentologic Two types of coarse-grained deltas are they commonly have a sheet geometry with implications. The term "fan-delta" is widely recognized: fan-deltas and braid deltas. Fan- high lateral continuity (tens to hundreds of used to describe depositional settings embracing deltas are gravel-rich deltas formed where an square kilometres); and they exhibit moderate a range of coarse-grained delta types other than alluvial fan is deposited directly into a stand- to high porosity and permeability. Valuable that of the fan-delta originally described by ing body of water from an adjacent highland. paleogeographic and tectonic information Holmes (1965). Many descriptions in the litera- They occupy a space between the highland concerning the proximity of highlands and ture of ancient fan-delta sequences contain no (usually a fault-bounded margin) and the major fault zones may be misinterpreted or evidence of the required presence of an alluvial standing body of water. In contrast, braid lost if these two coarse-grained deltaic sys- fan; instead they consist of deltaic deposits com- deltas (here introduced) are gravel-rich deltas tems are not differentiated. prising multilateral channel conglomerates and that form where a braided fluvial system pro- sandstones deposited from braided fluvial dis- grades into a standing body of water.
    [Show full text]
  • Hydrogeomorphic Processes and Torrent Control Works on a Large Alluvial Fan in the Eastern Italian Alps
    Nat. Hazards Earth Syst. Sci., 10, 547–558, 2010 www.nat-hazards-earth-syst-sci.net/10/547/2010/ Natural Hazards © Author(s) 2010. This work is distributed under and Earth the Creative Commons Attribution 3.0 License. System Sciences Hydrogeomorphic processes and torrent control works on a large alluvial fan in the eastern Italian Alps L. Marchi1, M. Cavalli1, and V. D’Agostino2 1Consiglio Nazionale delle Ricerche – Istituto di Ricerca per la Protezione Idrogeologica (CNR IRPI), Padova, Italy 2Dipartimento Territorio e Sistemi Agroforestali, Universita` di Padova, Legnaro (Padova), Italy Received: 17 November 2009 – Revised: 26 February 2010 – Accepted: 8 March 2010 – Published: 23 March 2010 Abstract. Alluvial fans are often present at the outlet of 1 Introduction small drainage basins in alpine valleys; their formation is due to sediment transport associated with flash floods and Alluvial fans at the outlet of small, high-gradient drainage debris flows. Alluvial fans are preferred sites for human set- basins are a common feature of alpine valleys. Although de- tlements and are frequently crossed by transport routes. In bris flows commonly dominate the formation and develop- order to reduce the risk for economic activities located on or ment of these alluvial fans, also bedload and hyperconcen- near the fan and prevent loss of lives due to floods and de- trated flows contribute to the transfer of sediment from the bris flows, torrent control works have been extensively car- drainage basin to the alluvial fan and its distribution on the ried out on many alpine alluvial fans. Hazard management fan surface. These flow processes result in major risk when on alluvial fans in alpine regions is dependent upon reliable they encroach settlements and transport routes, which are of- procedures to evaluate variations in the frequency and sever- ten present on the alluvial fans of the European Alps.
    [Show full text]
  • Moving Water Shapes Land
    KEY CONCEPT Moving water shapes land. BEFORE, you learned NOW, you will learn •Erosion is the movement of • How moving water shapes rock and soil Earth’s surface • Gravity causes mass movements • How water moving under- of rock and soil ground forms caves and other features VOCABULARY EXPLORE Divides drainage basin p. 579 How do divides work? divide p. 579 floodplain p. 580 PROCEDURE MATERIALS alluvial fan p. 581 •sheet of paper 1 Fold the sheet of paper in thirds and tape delta p. 581 • tape it as shown to make a “ridge.” sinkhole p. 583 •paper clips 2 Drop the paper clips one at a time directly on top of the ridge from a height of about 30 cm. Observe what happens and record your observations. WHAT DO YOU THINK? How might the paper clips be similar to water falling on a ridge? Streams shape Earth’s surface. If you look at a river or stream, you may be able to notice something about the land around it. The land is higher than the river. If a river is running through a steep valley, you can easily see that the river is the low point. But even in very flat places, the land is sloping down to the river, which is itself running downhill in a low path through the land. NOTE-TAKING STRATEGY Running water is the major force shaping the landscape over most A main idea and detail of Earth. From the broad, flat land around the lower Mississippi River notes chart would be a good strategy to use for to the steep mountain valleys of the Himalayas, water running downhill taking notes about streams changes the land.
    [Show full text]
  • Alluvial Fans
    GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111 Lecture Note Series Sedimentary Environments 1: Alluvial Fans Lecture Goals A) Depositional/Sedimentary Environments B) Alluvial fan depositional environments C) Sediment and rocks that form on alluvial fans Reference: Press et al., 2004, Chapter 7; Grotzinger et al., 2007, Chapter 18, p 449 GY 111 Lab manual Chapter 3 Note: At this point in the course, my version of GY 111 starts to diverge a bit from my colleagues. I tend to focus a bit more on sedimentary processes then they do mostly because we live in an area that is dominated by sedimentation and I figure that you should be as familiar as possible with the subject. As it turns out, the web notes are also more comprehensive than what you'll find in your text book A) Depositional/sedimentary environments Last time we met, we discussed how sediment moved from one place to another. Remember that sediment is produced in a lot of different locations, but it seldom stays where it is produced. The action of water, wind and ice transport it from the sediment source to the sediment sink. The variety of sediment sinks that exist on the planet is truly amazing. There are river basins, lakes, deserts, lagoons, swamps, deltas, beaches, barrier islands, reefs, continental shelves, the abyssal plains (very deep!), trenches (even deeper!) etc. As we discussed last time, these places are called depositional environments (also known as sedimentary environments). Each depositional environment may also have several subdivisions. For example, there are open beaches, sheltered beaches, shingle beaches, sand beaches, strandline beaches, even mud beaches.
    [Show full text]
  • 495 Unique Replogle Flume Installations at The
    UNIQUE REPLOGLE FLUME INSTALLATIONS AT THE TRUCKEE CARSON IRRIGATION DISTRICT Stuart Styles1 Brandon Downing2 Walter Winder3 ABSTRACT The Water Measurement Program (WMP) for Truckee Carson Irrigation District (TCID) began in 1997, when the Irrigation Training and Research Center (ITRC) of Cal Poly State University was asked to develop a volumetric measurement plan for TCID, funded by the U.S. Bureau of Reclamation, Mid-Pacific Region. This program was intended to develop and install reasonably accurate turnout delivery measurement techniques in the district. As part of the WMP, TCID was required to install a number of new open- channel measurement devices. TCID opted for the Replogle flume as its primary flow measurement device using the newly developed WinFlume computer program. A few key problems prevented TCID from using the typical Replogle flume design that is used in most irrigation districts. For example, the majority of flow measurement sites were to be installed in earthen channels. In addition, the head loss available at each of the sites was relatively small for this type of structure. This required a new design where the cross section and the ramp portion of the flume had to be incorporated in the same construction package. The process used in the design and the unique aspects of construction used on these projects are documented in this paper. INTRODUCTION With demand on worldwide water supplies continually increasing, it is necessary to find ways to both improve the efficiency of its use as well as promote conservation. In order to achieve these simultaneous goals, good water management is required that relies on effective and practical flow measurement.
    [Show full text]
  • Flooding Dynamics in a Large Low-Gradient Alluvial Fan, the Okavango Delta, Botswana, from Analysis and Interpretation of a 30-Year Hydrometric Record
    Hydrology and Earth System Sciences, 10, 127–137, 2006 www.copernicus.org/EGU/hess/hess/10/127/ Hydrology and SRef-ID: 1607-7938/hess/2006-10-127 Earth System European Geosciences Union Sciences Flooding dynamics in a large low-gradient alluvial fan, the Okavango Delta, Botswana, from analysis and interpretation of a 30-year hydrometric record P. Wolski and M. Murray-Hudson Harry Oppenheimer Okavango Research Centre, Maun, Botswana Received: 11 August 2005 – Published in Hydrology and Earth System Sciences Discussions: 6 September 2005 Revised: 29 November 2005 – Accepted: 3 January 2006 – Published: 21 February 2006 Abstract. The Okavango Delta is a flood-pulsed wetland, tem, and the flood frequency distribution itself can change, which supports a large tourism industry and the subsistence compared to that at upstream locations (Wolff and Burges, of the local population through the provision of ecosystem 1994). The ecological role of the channel-floodplain interac- services. In order to obtain insight into the influence of var- tion is expressed by the flood pulse concept (Junk et al., 1989; ious environmental factors on flood propagation and distri- Middleton, 1999). According to this concept, floodplain wet- bution in this system, an analysis was undertaken of a 30- lands and riparian ecosystems adjust to, and are maintained, year record of hydrometric data (discharges and water lev- by the pulsing of water, sediment and nutrients that occurs els) from one of the Delta distributaries. The analysis re- during over-bank flow conditions. Odum (1994) addition- vealed that water levels and discharges at any given channel ally identifies flood pulsing at various spatial and temporal site in this distributary are influenced by a complex interplay scales as an energy subsidy to wetland ecosystems, explain- of flood wave and local rainfall inputs, modified by channel- ing in part the high ecological productivity associated with floodplain interactions, in-channel sedimentation and techni- such systems.
    [Show full text]
  • Alluvial Fan Hazards & Design Issues for Design
    Presentation Program Outline Overview Countermeasures / Planning Process Levees / Dikes / Diversions Channelization / Conveyance Grade Control Structures Detention Basin / Debris Basin Case Study – Localized Subdivision Protection (THOUSAND PALMS, CA) Case Study – Whole Fan Facilities (INDIAN WELLS, CA) Structural Countermeasures Overview / Planning Process & Design Considerations Alluvial Fan Hazards & Design Issues for Design • Uncertainty of flow depths (R&U analysis) • Inundation extents / flow direction / impingement • Sediment deposition • Scouring and undermining • Impact forces • Channel avulsions and entrenchments • Hydrostatic and buoyant forces • High velocities • Unpredictable flow path (R&U analysis) • Flooding from both debris and water flows “Riverine” vs. “Alluvial Fan” - Structural Countermeasure Design Issues / Considerations • Flow uncertainty • Velocity • Flow duration • Sediment deposition • Seepage control • Impingement • Flow direction and path uncertainty Alluvial Fan Riverine “Whole Fan” Solutions vs. Localized Protection – Structural Countermeasures “Whole Fan” Solutions vs. Localized Protection – Structural Countermeasures Structural Countermeasures for Alluvial Fans – Basic Building Blocks Collection Channels Conveyance Channels Dispersion Channels Structural Countermeasures for Alluvial Fans – Basic Building Blocks - Example Standard Alluvial Fan Structural Countermeasures Effectiveness of Alluvial Fan Structural Countermeasures for Different Hazards Structural Countermeasure – General Design Considerations
    [Show full text]
  • Flume Test Simulation and Study of Salt and Fresh Water Mixing Influenced by Tidal Reciprocating Flow
    water Article Flume Test Simulation and Study of Salt and Fresh Water Mixing Influenced by Tidal Reciprocating Flow Weiyi Xia *, Xiaodong Zhao, Riming Zhao and Xinzhou Zhang Key Laboratory of Port, Waterway and Sedimentation Engineering of the Ministry of Transport, Nanjing Hydraulic Research Institute, Nanjing 210029, China; [email protected] (X.Z.); [email protected] (R.Z.); [email protected] (X.Z.) * Correspondence: [email protected]; Tel.: +86-1381-306-6839 Received: 19 February 2019; Accepted: 18 March 2019; Published: 20 March 2019 Abstract: The salt-fresh water mixing is one of the basic topics of estuarine dynamics research. In partially mixed and highly stratified mixed estuaries, the structure of stratified flow is complicated by density gradient and tidal reciprocating flow. The velocity and salinity structures have been experimentally studied in a flume which is 167.8 m long, 0.5 m wide, and 0.5 m deep. The processes of the tidal levels, the flood and ebb current, and the salt-fresh water mixing have been simulated. Furthermore, the partially mixed and highly stratified mixed types have been repeatability showed in the flume, by solving the problems of experiment control and saltwater recycling. The control variable method has been used to dialectically analyze the influence of tidal range and runoff volume on the velocity and salinity distribution. The tide and runoff are respectively considered to affect the mixing type in two contradictory ways. In the condition of tidal reciprocating flow, the periodical change of interface stability has been investigated. It is considered that the interface stability is closely related to the vertical gradient of density and velocity.
    [Show full text]
  • Flooding Dynamics in a Large Low-Gradient Alluvial Fan, the Okavango Delta, Botswana, from Analysis and Interpretation of a 30-Year Hydrometric Record
    Hydrol. Earth Sys. Sci. Discuss., 2, 1865–1892, 2005 Hydrology and www.copernicus.org/EGU/hess/hessd/2/1865/ Earth System SRef-ID: 1812-2116/hessd/2005-2-1865 Sciences European Geosciences Union Discussions Papers published in Hydrology and Earth System Sciences Discussions are under open-access review for the journal Hydrology and Earth System Sciences Flooding dynamics in a large low-gradient alluvial fan, the Okavango Delta, Botswana, from analysis and interpretation of a 30-year hydrometric record P. Wolski and M. Murray-Hudson Harry Oppenheimer Okavango Research Centre, Maun, Botswana Received: 11 August 2005 – Accepted: 22 August 2005 – Published: 6 September 2005 Correspondence to: P. Wolski ([email protected]) © 2005 Author(s). This work is licensed under a Creative Commons License. 1865 Abstract The Okavango Delta is a flood-pulsed wetland, the resources of which support a large tourism industry and subsistence of the local population. In order to obtain an insight into the influence of various environmental factors on flood propagation and distribution 5 in this system, an analysis was undertaken of a 30-year record of hydrometric data (dis- charges and water levels) from one of the Delta distributaries. The analysis revealed that water levels and discharges at any given channel site in the analysed distributary are influenced by a complex interplay of flood wave and local rainfall input modified by channel-floodplain interactions, in-channel sedimentation and technical interventions, 10 both at the given site and upstream. Additionally, cyclical variation of channel margin vegetation due to nutrients recycling might play a role. It was shown that data from channels do not adequately represent flood dynamics and its change at the distribu- tary level.
    [Show full text]
  • Vanwaltconnect Telemetry System and RBC Flume Installation
    Measuring and recording open channel flow with the vanwaltCONNECT telemetry system and RBC flume. Measuring water flow in a river. Council bodies measure river flow by mapping riverbed cross sections and recording the water level at these cross sections. Careful correlation of this data with time stamps allows a calculation of water flow that can be fine-tuned with manual flow gauging. When measuring water flow to the nearest cubic meter per second this method will suffice but with smaller bodies of water it becomes woefully inaccurate. A calibrated flume is required to calculate water flow to the nearest Litre per second. What is a flume. Flumes are specially shaped, engineered structures that are used to measure the flow of water in open channels. Flumes have no moving parts. They rely on restricting the flow of water in such a way so as to develop a relationship between the water level in the flume at the point of measurement and the flow rate. Flumes can use a change in elevation, a contraction of the sidewalls or a combination of the two to accelerate flow. This acceleration creates upstream conditions where the flow rate can be determined by measuring the water level at a single point. The water level is measured in a stilling well that is connected to the main body of water by a small capillary. This ensures that the measurement is unaffected by surface distortion (waves, current) The relationship between the water level at the point of measurement and the flow rate can be obtained by a derived formula.
    [Show full text]