DOCSLIB.ORG

Coastal and Shelf Sediment Transport: an Introduction

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Coastal and Shelf Sediment Transport: an Introduction Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 Coastal and shelf sediment transport: an introduction MICHAEL B. COLLINS 1'3 & PETER S. BALSON 2 1School of Ocean & Earth Science, University of Southampton, Southampton Oceanography Centre, European Way, Southampton S014 3ZH, UK (e-mail." mbc@noc, soton, ac. uk) 2Marine Research Division, AZTI Tecnalia, Herrera Kaia, Portu aldea z/g, Pasaia 20110, Gipuzkoa, Spain 3British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK. Interest in sediment dynamics is generated by the (a) no single method for the determination of need to understand and predict: (i) morphody- sediment transport pathways provides the namic and morphological changes, e.g. beach complete picture; erosion, shifts in navigation channels, changes (b) observational evidence needs to be gathered associated with resource development; (ii) the in a particular study area, in which contem- fate of contaminants in estuarine, coastal and porary and historical data, supported by shelf environment (sediments may act as sources broad-based measurements, is interpreted and sinks for toxic contaminants, depending by an experienced practitioner (Soulsby upon the surrounding physico-chemical condi- 1997); tions); (iii) interactions with biota; and (iv) of (c) the form and internal structure of sedimen- particular relevance to the present Volume, inter- tary sinks can reveal long-term trends in pretations of the stratigraphic record. Within this transport directions, rates and magnitude; context of the latter interest, coastal and shelf (d) complementary short-term measurements sediment may be regarded as a non-renewable and modelling are required, to (b) (above) -- resource; as such, their dynamics are of extreme any model of regional sediment transport importance. Over the years, various approaches must account for the size, location and and techniques have been applied to the determi- composition of sedimentary sinks. nation of sediment transport pathways and the derivation of erosion, transport, and deposition On the basis of the above summary, it is evident rates. Such wide-ranging approaches include the that it is timely to review a representative selec- refinement and application of numerical model- tion of the different approaches, by reference to ling; and the development of new and more effi- recently undertaken coastal and shelf investiga- cient field equipment, e.g. video systems (coastal/ tions. A number of such studies (13) are included inshore) and multibeam. within this Special Publication, operating at a In general, sediment transport can be defined variety of temporal and spatial scales, within dif- on the basis of direct observations, indirect obser- ferent regions of the UK/European continental vations and by modelling. Direct observation shelf, and elsewhere. methods include: acoustic backscatter; optical The concept of different scales, in relation backscatter; sediment traps; artificial tracers, for to sediment dynamics has been proposed sand and pebbles; natural tracers or labelled sedi- (Horikawa 1970) for classifying coastal phenom- ments, for silts and clays; and the determination ena into three (temporal and spatial) categories: of water movements, using drifters, SPM (sus- macroscale (year/kilometre); mesoscale (day- pended particulate matter) and remote sensing. hour/metre); and microscale (second/millimetre). Indirect observational methods include: sediment Subsequently, the following observations have characteristics, including GSTA (grain size been made (Horikawa 1981): trend analysis) and mineralogy; geomorphology, (a) to treat the macroscale phenomena, the including coastal landforms, estuarine volumes approach of the geologist and geomorph- and asymmetric bedforms (ripples, sandwaves ologist is helpful for understanding the and sandbanks); and, finally, the internal struc- general tendencies of the coastal processes; ture of the sediment bodies (cross-bedding and (b) changes in shoreline and sea-bottom topog- accretionary sequences). On the basis of these raphy, bar and cusp formation, together various approaches and techniques, it may be with nearshore currents, all fall into the concluded that: category of mesoscale phenomena; From: BALSON,P. S. & COLLINS, M. B. 2007. Coastaland Shelf Sediment Transport. Geological Society of London, Special Publications, 274, 1-5.0305-8719107l$15.00 9 The Geological Societyof London 2007. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 2 M.B. COLLINS & P. S. BALSON (c) within the context of a microscale approach, phenomena, the macroscale phenomena. At the extensive research needs were identified time of the publication (Horikawa 1981), such such as, in particular, various aspects of connections could not be made. wave-current interaction. The above concept has been developed further by Larson & Kraus (1995), in relation to Interestingly, the observation is made that, spatial and temporal scales for investigating theoretically, the complete superposition of sediment transport and morphological processes. microscale phenomena should compose the In Figure 1, microscale is seen to refer to changes mesoscale phenomena and that of mesoscale from sub-wave period to several periods, over Fig. 1. Relationships of contributions to the Special Publication, in terms of their spatial and temporal scales (based upon Larson & Kraus 1995). Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 INTRODUCTION 3 lengths of millimetres to centimetres. At mesos- suspended sediment component close to the bed, cale, net transport rates over many wave periods together with the bedload itself. The labelling are evaluated for distances of metres to a kilo- of pure clays and estuarine sediments, with metre. Macroscale involves seasonal changes lanthanide (La) is described by Spencer et al. and a space scale of kilometres, whilst megascale Here, it is concluded that further investigation describes decade to century changes over coastal is required, of the use of alternative lanthanide sub-reaches and reaches, e.g. over a littoral cell. group elements, for such studies. Optical and The concepts applied here are applicable, acoustic backscatter sensors are described then equally, to the inner continental shelf (< 60 m (Bass et al.), within the context of the mea- water depth) - at the very least. The main conclu- surements of the mud and sand component in sions reached (Larsen & Kraus 1995) are that transit, at a site located to seawards of the Wash calculations at different scales can be related embayment, southern North Sea. and reconciled, if limitations in the predictions The problems of field measurements and of initial and boundary conditions and in the quantification of longshore sediment transport fluid flow, are recognised. Against this back- (LST) is considered by Cooper & Pilkey, in terms ground the contribution of the present pub- of mechanisms and present approaches. It is lication are superimposed; these range from pointed out, by these authors, that the inability micro- to mega-scales, on the basis of the to measure the total LST has important implica- generalized classification. tions for coastal zone management; this is Interestingly, Dronkers (2005) has adopted a because so many coastal management initiatives similar approach, based upon the original synthe- sis of Holman (2001). The former investigator rely upon quantified volumes of LST. In terms of makes the following pertinent observations: coastal and shelf seas, in general, a relatively simple analytic (algebraic) approach is described (a) at small spatial scales, seabed morphology (Aldridge), to complement full-scale numerical and water motion adapt to each other, with calculations and assist in the interpretation of a short delay, but at a large spatial scale, the the numerical results. However, the results adaptation period can be very long; obtained rely upon the implicit assumption that (b) if erosion and sedimentation are balanced, the supply of material available for transport is averaged over large temporal and spatial scales, it may happen that these is an imbal- not exhausted, over the tidal cycle. ance at smaller scales or vice versa - in fact, The repeated survey of banner tidal sand- the phenomena of erosion, sedimentation banks, using multibeam, is described by Schmidt and sediment transport always have to be et al. Interestingly, dunes connect over the crest defined with respect to particular spatial and of the bank despite opposing sediment transport temporal scales; directions on the flanks. A new numerical model, (c) the physics of sedimentary coastal environ- that identifies the paths taken by a large number ments is related to temporal and spatial of identified ('tagged') sand grains in coastal scales - the physical processes that deter- areas in response to waves and currents, is mine coastal morphology span a range of described by Soulsby et al. Within this context, temporal scales, covering more than ten a validation exercise is applied simulating the orders of magnitude. dispersal of radioactive sand tracers. Particle tracking is considered, in terms of a somewhat For large temporal, but small spatial scale pro- cesses, time-series are restricted; sometimes, they different approach, by Black et al. Used in are not of sufficient high quality to overcome conjunction with a range of more traditional any uncertainties, i.e. separating processes from methods, particle tracking (particle
Load more

Recommended publications
  • Sediment Transport in the San Francisco Bay Coastal System: an Overview
    Marine Geology 345 (2013) 3–17 Contents lists available at ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margeo Sediment transport in the San Francisco Bay Coastal System: An overview Patrick L. Barnard a,⁎, David H. Schoellhamer b,c, Bruce E. Jaffe a, Lester J. McKee d a U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA, USA b U.S. Geological Survey, California Water Science Center, Sacramento, CA, USA c University of California, Davis, USA d San Francisco Estuary Institute, Richmond, CA, USA article info abstract Article history: The papers in this special issue feature state-of-the-art approaches to understanding the physical processes Received 29 March 2012 related to sediment transport and geomorphology of complex coastal–estuarine systems. Here we focus on Received in revised form 9 April 2013 the San Francisco Bay Coastal System, extending from the lower San Joaquin–Sacramento Delta, through the Accepted 13 April 2013 Bay, and along the adjacent outer Pacific Coast. San Francisco Bay is an urbanized estuary that is impacted by Available online 20 April 2013 numerous anthropogenic activities common to many large estuaries, including a mining legacy, channel dredging, aggregate mining, reservoirs, freshwater diversion, watershed modifications, urban run-off, ship traffic, exotic Keywords: sediment transport species introductions, land reclamation, and wetland restoration. The Golden Gate strait is the sole inlet 9 3 estuaries connecting the Bay to the Pacific Ocean, and serves as the conduit for a tidal flow of ~8 × 10 m /day, in addition circulation to the transport of mud, sand, biogenic material, nutrients, and pollutants.
    [Show full text]
  • Progressive and Regressive Soil Evolution Phases in the Anthropocene
    Progressive and regressive soil evolution phases in the Anthropocene Manon Bajard, Jérôme Poulenard, Pierre Sabatier, Anne-Lise Develle, Charline Giguet- Covex, Jeremy Jacob, Christian Crouzet, Fernand David, Cécile Pignol, Fabien Arnaud Highlights • Lake sediment archives are used to reconstruct past soil evolution. • Erosion is quantified and the sediment geochemistry is compared to current soils. • We observed phases of greater erosion rates than soil formation rates. • These negative soil balance phases are defined as regressive pedogenesis phases. • During the Middle Ages, the erosion of increasingly deep horizons rejuvenated pedogenesis. Abstract Soils have a substantial role in the environment because they provide several ecosystem services such as food supply or carbon storage. Agricultural practices can modify soil properties and soil evolution processes, hence threatening these services. These modifications are poorly studied, and the resilience/adaptation times of soils to disruptions are unknown. Here, we study the evolution of pedogenetic processes and soil evolution phases (progressive or regressive) in response to human-induced erosion from a 4000-year lake sediment sequence (Lake La Thuile, French Alps). Erosion in this small lake catchment in the montane area is quantified from the terrigenous sediments that were trapped in the lake and compared to the soil formation rate. To access this quantification, soil processes evolution are deciphered from soil and sediment geochemistry comparison. Over the last 4000 years, first impacts on soils are recorded at approximately 1600 yr cal. BP, with the erosion of surface horizons exceeding 10 t·km− 2·yr− 1. Increasingly deep horizons were eroded with erosion accentuation during the Higher Middle Ages (1400–850 yr cal.
    [Show full text]
  • Sediment and Sedimentary Rocks
    Sediment and sedimentary rocks • Sediment • From sediments to sedimentary rocks (transportation, deposition, preservation and lithification) • Types of sedimentary rocks (clastic, chemical and organic) • Sedimentary structures (bedding, cross-bedding, graded bedding, mud cracks, ripple marks) • Interpretation of sedimentary rocks Sediment • Sediment - loose, solid particles originating from: – Weathering and erosion of pre- existing rocks – Chemical precipitation from solution, including secretion by organisms in water Relationship to Earth’s Systems • Atmosphere – Most sediments produced by weathering in air – Sand and dust transported by wind • Hydrosphere – Water is a primary agent in sediment production, transportation, deposition, cementation, and formation of sedimentary rocks • Biosphere – Oil , the product of partial decay of organic materials , is found in sedimentary rocks Sediment • Classified by particle size – Boulder - >256 mm – Cobble - 64 to 256 mm – Pebble - 2 to 64 mm – Sand - 1/16 to 2 mm – Silt - 1/256 to 1/16 mm – Clay - <1/256 mm From Sediment to Sedimentary Rock • Transportation – Movement of sediment away from its source, typically by water, wind, or ice – Rounding of particles occurs due to abrasion during transport – Sorting occurs as sediment is separated according to grain size by transport agents, especially running water – Sediment size decreases with increased transport distance From Sediment to Sedimentary Rock • Deposition – Settling and coming to rest of transported material – Accumulation of chemical
    [Show full text]
  • Descriptions of Common Sedimentary Environments
    Descriptions of Common Sedimentary Environments River systems: . Alluvial Fan: a pile of sediment at the base of mountains shaped like a fan. When a stream comes out of the mountains onto the flat plain, it drops its sediment load. The sediment ranges from fine to very coarse angular sediment, including boulders. Alluvial fans are often built by flash floods. River Channel: where the river flows. The channel moves sideways over time. Typical sediments include sand, gravel and cobbles. Particles are typically rounded and sorted. The sediment shows signs of current, such as ripple marks. Flood Plain: where the river overflows periodically. When the river overflows, its velocity decreases rapidly. This means that the coarsest sediment (usually sand) is deposited next to the river, and the finer sediment (silt and clay) is deposited in thin layers farther from the river. Delta: where a stream enters a standing body of water (ocean, bay or lake). As the velocity of the river drops, it dumps its sediment. Over time, the deposits build further and further into the standing body of water. Deltas are complex environments with channels of coarser sediment, floodplain areas of finer sediment, and swamps with very fine sediment and organic deposits (coal) Lake: fresh or alkaline water. Lakes tend to be quiet water environments (except very large lakes like the Great Lakes, which have shorelines much like ocean beaches). Alkaline lakes that seasonally dry up leave evaporite deposits. Most lakes leave clay and silt deposits. Beach, barrier bar: near-shore or shoreline deposits. Beaches are active water environments, and so tend to have coarser sediment (sand, gravel and cobbles).
    [Show full text]
  • Soil Erosion, Runoff, and Sedimentation Construction Site Fact Sheet No
    Soil Erosion, Runoff, and Sedimentation Construction Site Fact Sheet No. 1 What Is Soil Erosion? What Problems Happen On Construction Soil erosion is the detachment and movement of soil Sites? particles by water, wind, ice, or gravity. Safety and Nuisance Issues – Sediment on roadways and in the air can cause safety hazards. Flooding– Excessive sediment accumulation in drainage systems can create blockages that promote flooding. Sediment Build‐Up – Sediment that accumulates in streams, lakes, and bays can only be remediated by costly dredging. Increased Costs – Uncontrolled erosion and sedimentation requires costly maintenance and What Is Sedimentation? repair. It is cheaper and easier to PREVENT Sediment is the result of erosion. Sedimentation is erosion than to fix sedimentation problems. the build‐ up of eroded soil particles that are transported in runoff from their site of origin and Negative Public Perception ‐Observing muddy deposited in drainage systems, on other ground water flowing from construction sites negatively surfaces, or in bodies of water or wetlands. effects public perception. Why Should I Care? It’s the Law– Federal, State and local regulations require construction sites to be compliant with the Clean Water Act. Water Quality‐Erosion from construction projects can be a non‐point source pollutant that deteriorates the health of our lakes, streams and Narragansett Bay. Soil Loss ‐ Much of the total sediment loss that occurs each year is generated by highway construction and land development projects. Quality of Life‐ If you enjoy fishing, eating local Sediment‐filled runoff from a RIDOT construction site shellfish or swimming at one of Rhode Island’s beautiful beaches, this pollution can threaten your quality of life.
    [Show full text]
  • Sedimentary Rocks
    Sedimentary Rocks • a rock resulting from the consolidation of loose sediment that has been derived from previously existing rocks • a rock formed by the precipitation of minerals from solution Sedimentary Stages of the Rock Cycle Weathering Erosion Transportation Deposition (sedimentation) Burial Diagenesis Fig. 5.1 1 Table 5.1 Sorting Fig 5.2 Transport will effect the sediment in several ways Sorting:Sorting a measure of the variation in the range of grain sizes in a rock or sediment • Well-sorted sediments have been subjected to prolonged water or wind action. • Poorly-sorted sediments are either not far- removed from their source or deposited by glaciers. 2 Fig. 5.3 Sedimentary Environments Fig. Story 5.5 Table 5.2 3 Sedimentary Structures Stratification = Bedding = Layering This layering that produces sedimentary structures is due to: • Particle size • Types (s) of particles Sedimentary Layering Other Examples of Sedimentary Structures • Cross-beds • Ripple marks • Mudcracks • Raindrop impressions • Fossils 4 Cross-bedded sandstone Fig. 5.6 Fig. 5.7 Ripples on a beach Fig. 5.8 5 Ripples Preserved in Sandstone Fig. 5.9 Fig. 5.9 6 Fig. 5.10 Turbidity Currents Suspension of water sand, and mud that moves downslope (often very rapidly) due to its greater density that the surrounding water (often triggered by earthquakes). The speed of turbidity currents was first appreciated in 1920 when a current broke lines in the Atlantic. This event also demonstrated just how far a single deposit could travel. From Sediment to Sedimentary Sock (lithification) • Compaction:Compaction reduces pore space. clays and muds are up to 60 % water; 10% after compaction • Cementation:Cementation chemical precipitation of mineral material between grains (SiO2, CaCO3, Fe2O3) binds sediment into hard rock.
    [Show full text]
  • Description of a Contourite Depositional System on the Demerara Plateau: Results from Geophysical Data and Sediment Cores
    1 Marine Geology Achimer August 2016, Volume 378, Pages 56-73 http://dx.doi.org/10.1016/j.margeo.2016.01.003 http://archimer.ifremer.fr http://archimer.ifremer.fr/doc/00308/41957/ © 2016 Elsevier B.V. All rights reserved Description of a contourite depositional system on the Demerara Plateau: Results from geophysical data and sediment cores Tallobre Cédric 1, 2, *, Loncke Lies 1, 2, Bassetti Maria-Angela 1, 2, Giresse Pierre 1, 2, Bayon Germain 3, Buscail Roselyne 1, 2, Durrieu De Madron Xavier 1, 2, Bourrin François 1, 2, Vanhaesebroucke Marc 1, 2, Sotin Christine 1, 2, Iguanes Scientific Party 1 Univ. Perpignan Via Domitia, Centre de Formation et de Recherche sur les Environnements Méditerranéens (CEFREM), UMR 5110, 52 Avenue Paul Alduy, 66860 Perpignan, France 2 CNRS, Centre de Formation et de Recherche sur les Environnements Méditerranéens (CEFREM), UMR 5110, 52 Avenue Paul Alduy, 66860 Perpignan, France 3 IFREMER, Unité de Recherche Géosciences Marines, 29280 Plouzané, France * Corresponding author : Cédric Tallobre, email address : [email protected] Abstract : The Demerara Plateau, belonging to the passive transform margin of French Guiana, was investigated during the IGUANES cruise in 2013. The objectives of the cruise were to explore the poorly-known surficial sedimentary column overlying thick mass transport deposits as well as to understand the factors controlling recent sedimentation. The presence of numerous bedforms at the seafloor was observed thanks to newly acquired IGUANES bathymetric, high resolution seismic and chirp data, while sediment cores allowed the characterization of the deposits covering the mass transport deposits. Modern oceanographic conditions were determined in situ, using mooring monitoring over a 10-month period.
    [Show full text]
  • Simulation of Flow, Sediment Transport, and Sediment Mobility of the Lower Coeur D’Alene River, Idaho
    Prepared in cooperation with the Idaho Department of Environmental Quality, Basin Environmental Improvement Commission, and the U.S. Environmental Protection Agency Simulation of Flow, Sediment Transport, and Sediment Mobility of the Lower Coeur d’Alene River, Idaho Scientific Investigations Report 2008–5093 U.S. Department of the Interior U.S. Geological Survey Simulation of Flow, Sediment Transport, and Sediment Mobility of the Lower Coeur d’Alene River, Idaho By Charles Berenbrock and Andrew W. Tranmer Prepared in cooperation with the Idaho Department of Environmental Quality, Basin Environmental Improvement Commission, and the U.S. Environmental Protection Agency Scientific Investigations Report 2008–5093 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia: 2008 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS--the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Berenbrock, Charles, and Tranmer, A.W., 2008, Simulation of flow, sediment transport, and sediment mobility of the Lower Coeur d’Alene River, Idaho: U.S.
    [Show full text]
  • 2. Sediments and Biogeochemistry
    2. Sediments and Biogeochemistry Benthic size classes Properties of marine sediments Sediment biogeochemistry Chemical gradients in sediments Biological mediation Physical flow effects Dr Laura J. Grange ([email protected]) 11th April 2010 Reading: Levinton, Chapter 13, “Life in the Mud and Sand” Benthic Organisms Sizes Nanobenthos (microflora/microfauna) <62µm (shallow-water) <42µm (deep-sea) Meiofauna 62µm – 500µm (shallow-water) 42µm – 300µm (deep-sea) Macrofauna 500µm – 3cm (shallow-water) 300µm – 3cm (deep-water) Megafauna >3cm Large enough to be identified by bottom photos Marine Sediments Actual sizes not as important as recognizing scale Marine Sediments Rarely consist of just one size fraction What factors are important to biology? Surface area How much space available for colonization grain size = available surface area per gram Mayer & Rossi, 1982 Marine Sediments Water Marine sediments are overlain by seawater of varying depth Water penetrates into sediment, bringing with it chemicals, nutrients & O2 Ability of water to penetrate and move is characterized by :- Porosity Measure of space within sediment that can be occupied by water Permeability Measure of ability of water to flow through sediment Marine Sediments Porosity Lowest in sands Highest in silts and clays Permeability Highest is sands Lowest in silts and clays Both factors affect pore water chemistry Diffusion usually slow through sediments Path water takes among sediment grains is long High tortuosity Friedman et al.,
    [Show full text]
  • Why and How Do We Study Sediment Transport? Focus on Coastal Zones and Ongoing Methods
    water Editorial Why and How Do We Study Sediment Transport? Focus on Coastal Zones and Ongoing Methods Sylvain Ouillon ID LEGOS, Université de Toulouse, IRD, CNES, CNRS, UPS, 14 Avenue Edouard Belin, 31400 Toulouse, France; [email protected]; Tel.: +33-56133-2935 Received: 22 February 2018; Accepted: 22 March 2018; Published: 27 March 2018 Abstract: Scientific research on sediment dynamics in the coastal zone and along the littoral zone has evolved considerably over the last four decades. It benefits from a technological revolution that provides the community with cheaper or free tools for in situ study (e.g., sensors, gliders), remote sensing (satellite data, video cameras, drones) or modelling (open source models). These changes favour the transfer of developed methods to monitoring and management services. On the other hand, scientific research is increasingly targeted by public authorities towards finalized studies in relation to societal issues. Shoreline vulnerability is an object of concern that grows after each marine submersion or intense erosion event. Thus, during the last four decades, the production of knowledge on coastal sediment dynamics has evolved considerably, and is in tune with the needs of society. This editorial aims at synthesizing the current revolution in the scientific research related to coastal and littoral hydrosedimentary dynamics, putting into perspective connections between coasts and other geomorphological entities concerned by sediment transport, showing the links between many fragmented approaches of the topic, and introducing the papers published in the special issue of Water on “Sediment transport in coastal waters”. Keywords: sediment transport; cohesive sediments; non cohesive sediments; sand; mud; coastal erosion; sedimentation; morphodynamics; suspended particulate matter; bedload 1.
    [Show full text]
  • Sediment Basins `
    SC DHEC Stormwater BMP Handbook Sediment Control BMPs – Sediment Basins ` Sediment Basins FEATURES • Sediment Control • Volume Control • Velocity Control SECTIONS • General Design • Forebays • Porous Baffles • Basin Dewatering • Skimmers • Spillways • Permanent Pools Introduction • Maintenance Sediment Basins are a Best Management Practice (BMP) used to • Design Aids collect and impound stormwater runoff from disturbed areas (typically ALSO ADDRESSED 5 acres or more) at construction sites to restrict sediments and other pollutants from being discharged off-site. These basins may also be • Inlet Protection used to control the volume and velocity of the runoff through a timed release by utilizing multiple spillways. It is through this attenuation of • Basin Safety runoff that sediment basins may be capable of meeting South • Sediment Storage Carolina’s Design Requirements, specifically the Total Suspended Solids (TSS) removal efficiency of 80%. • Slope Stabilization These basins work most effectively in conjunction with additional • Rock Berms sediment and erosion control BMPs installed and maintained up • Outlet Protection gradient of the basins. • Basin Removal Guidance Disclaimer This is a guidance document and may not be feasible in all situations. Alternative means and methods for sediment basin design and PLAN SYMBOL construction also may be employed. All means and methods must comply with the DHEC South Carolina NPDES General Permit for Stormwater Discharges from Construction Activities (Permit). Approved means and methods include those published and approved by an MS4 in compliance with the Permit. In addition, a licensed Professional Engineer may design a sediment basin that, when constructed, accommodates the anticipated sediment loading from the land-disturbing activity and meets a removal efficiency of 80% suspended solids or 0.5 ML/L peak settable solids concentration, whichever is less, while remaining in compliance with the Permit.
    [Show full text]
  • Chapter 3 Sedimentary Rocks
    Chapter 3 Sedimentary Rocks Rivers that flow into the Gulf of Mexico through Alabama and other Gulf Coast states are typically brown, yellow-orange or red in color due to the presence of fine particulate material suspended within the water column. This particulate material is called sediment, and it was produced through the erosion and weathering of rocks exposed far inland from the coast (including the Appalachian Mountains). Sediment transported by rivers eventually finds its way into a standing body of water. Sometimes this is a lake or an inland sea, but for those of us that reside in southern Alabama, it is almost always the Gulf of Mexico. When rivers enter standing bodies of water (e.g., the Gulf), the sediment load that they are carrying is dropped and deposition occurs. Usually deposition forms more or less parallel layers called strata. Given time, and the processes of compaction and cementation, the sediment may be lithified into sedimentary rock. It is important to note that deposition of sediment is not restricted to river mouths. It also occurs on floodplains surrounding rivers, on tidal flats, adjacent to mountains in alluvial fans, and in the deepest portions of the oceans. Sedimentation occurs everywhere and this is one of the reasons why your humble author finds sedimentary geology so fascinating. Sedimentary rocks comprise approximately 30% of all of the rocks exposed at the Earth's surface. Those that are composed of broken rock fragments formed during erosion of bedrock are termed siliciclastic sedimentary rocks (or clastic for short). Sedimentary rocks can also be produced through chemical and biochemical deposition.
    [Show full text]