Application Guide - NexSens Technology Inc.
Contents
1. LY NA SB IN NAN ANANIZ xX ars AD AER DA WHAT S INSIDE 01 Bridge Scour Overview of FHWA Guidance and HEC Manuals 02 Sediment The Foundation of Scour 04 AReal Time Solution 06 Typical Scour Monitoring System 08 Points of Compliance 10 Data Management 12 Quality Assurance 14 Recommended Equipment 16 Purchase or Rent 17 About Fondriest Environmental 18 System Configuration Tool WHY MONITORING MATTERS Streambed scour is the erosion of sediment at the base of bridge piers abutments and other underwater structures Scouring can occur in any area of water flow from streams and rivers to tidal estuaries This erosion is caused by water flow and increases during times of high flow such as during a flood As flow speeds increase so does the potential for sediment transport The holes left behind in the riverbed by scour Can compromise structural integrity Bridge scour monitoring and scour monitoring at other offshore structures can identify and prevent disasters before they strike As scour alters the elevation of the riverbed at a pier a monitoring system can indicate when a bridge becomes structurally deficient and dangerous due to sediment erosion While monitoring does not make a structure less susceptible to scour a real time alert can be sent out if a bridge becomes scour critical and must be closed The Federal Highway Administration FHWA requires every state to ident2. can be easy to install during low flow events However they are very susceptible to debris in the water Automatic mag netic sliding collar systems are more expensive but also more robust than their manual counterparts However in biologically active environments such as estuaries and tidal rivers barnacle growth and other biofouling can occur This can interfere with scour readings as the biofouling can prevent the ring from moving down the rod Both versions of the sliding collar method should be firmly driven into the streambed Installations are easier in shallow rivers and during low flow events In addition to debris and biofouling sliding collars are susceptible to subsoil shifts Any lateral movement of a waterway can make the deploy ment ineffective Float out devices are buried at varying depths in a potential scour area When scour occurs removing the sediment covering the device the instru ment will float to the surface A wireless signal is transmitted to a nearby data logger to indicate its release These instruments have an extended lifespan 5 10 years for battery oper ated float outs to maintain operability for several seasons if they are not triggered in the first year As they are buried beneath the bed they are not susceptible to damage from debris at all They are also very easy to install in dry beds intermittent streams and riprap though they can also be installed in wet channels with a trained diver Whi
3. flood events PIER WATER SURFACE SEDIMENT BED When sediment transport removes material from a streambed or bank the erosion process is called scour Scour can occur anywhere that there is water flow and erodible material Local scour is the engineering term for the iso lated removal of sediment at one location such as the base of underwater structures including bridge piers and abutments This localized erosion can cause structural failure as bridges and overwater constructions rely on the bed sediment for support While scour can occur anywhere it is more likely to occur in alluvial water ways erodible bed and banks as opposed to a bedrock based nonalluvial channel As water flow is responsible for conducting sediment transport scour can occur even during low flow conditions However critical bridge scour conditions typically occur during periods of high flow such as during a flood event The higher flow rate can pick up more sediment and turbu lence often occurs at the base of a pier as it interrupts and accelerates the flow This turbulence in turn will increase the forces acting on a streambed suspending additional particles and initiating greater sediment transport If too much sediment is removed the structure can collapse Scour due to flood initiated sediment transport is the most common cause of bridge failure in the United States FONDRIEST COM 3 A REAL TIME SOLUTION One of the most effic
4. sensors and structure monitors provides useful data for scour research and offer a more thorough approach to scour monitoring Extra instrumentation often includes water level sensors stage sensors velocity or flow sensors temperature sensors and tiltmeters The use of additional sensors is more common with grant funded or USGS partnered projects as the supplementary data can be col lected for more accurate scour predictions and modeling These additional sensors can easily be connected to the monitoring station data logger for data transmission ABUTMENT PIER eee ae VERTICAL LATERAL RIVER STREAM SCOUR SCOUR mai INSTABILITY INSTABILITY TYPE SIZE VELOCITY MAGNETIC SLIDING COLLAR FLOAT OUT DEVICE BED ICE DEBRIS BANK MATERIAL LOAD SLOPE MAGNETIC SLIDING COLLAR SAND FINE FLOAT OUT DEVICE SAND FINE DATA REMOTE MAXIMUM MONITORING TECHNOLOGY RANGE MAGNETIC SLIDING COLLAR CONTINUOUS FLOAT OUT DEVICE DISCREET KEP EA HABIT DEPTH POSSIBLE FLOW WATER EXTREME FOUNDATION CONDITIONS TYPE EPHEMERAL INTERMITTENT MAINTENANCE MEDIUM FONDRIEST COM 9 DATA MANAGEMENT A major part of bridge scour monitoring is the need for raw data While it is possible to visit a site to periodically measure riverbed elevation a real time scour monitoring system is generally more cost effective The ability to frequently measure log and download the monitoring data in real time mean
5. viewed instantly at any time 24 7 through an online datacenter This data can be viewed in real time or as a graph to see trends Automated alerts can be sent in real time via text or email when scouring causes a structure to become dangerous Integrated Data Logging System 7 An integrated data logging system is a real time monitoring station that houses the data logger telemetry module and power charging supply Since it is generally cost prohibitive to run AC k al Mounting Hardware Data loggers can be mounted directly to the power to the monitoring location integrated solar panels are used to continuously charge the 12VDC battery for autonomous operation pier abutment or to a pole on the bridge depending on the location and recommended monitoring plan The sonar sensor s should be mounted to a bracket on the pier or abutment while water level or flow sensor s should be deployed in a fixed pipe SO oT 1 Sonar Depth Sensor Sonar instruments are commonly used to monitor scour as they measure the distance to the riverbed A sonar depth sensor can frequently ping the river bottom to detect if sediment has shifted or washed away changing the bed elevation Single beam sonar are best for monitoring one location while multi beam sonar can monitor a wider area FONDRIEST COM 7 MONITORING AS A COUNTERMEASURE The number location and even method of scour moni toring stations will vary due to lo
6. 25 and 50 ft Between 50 and 100 ft gt 100ft Water Level Fluctuation Sonar sensors need to be mounted below minimum pool in order to effectively measure distance to bottom st Between 5 and 25 ft Between 25 and 50 ft Other Please Specify Telemetry License free spread spectrum radio telemetry allows communication with a shore side NexSens radio base station as far as ive miles line of sight from the monitoring site Cellular telemetry allows greater geographic flexibility and is able to transmit from almost anywhere in the U S but it includes the cost of a cellular data plan Satellite telemetry can be used nearly anywhere in the world but it tends to have the highest data cost compared with cellular telemetry Cellular Radio Satellite None Project Length Rental vs Purchase Although it often makes sense to purchase systems outright many short term projects make it cost prohibitive Fondriest Environmental offers real time scour monitoring systems with weekly and monthly rental rates to accommodate these operations An application specialist can make recommenda tions on what choice is most cost effective 1 3 Months 3 6 Months 6 12 Months gt 1Year Please Specify FONDRIEST COM 19 FONDRIEST N ENVIRONMENTAL Fondriest Environmental Inc 2091 Exchange Court Fairborn OH 45324 888 426 2151 937 426 1125 O customercare fondriest com MIX Paper from res
7. Book pages or uploaded into the project s Media page The WQData LIVE report feature allows data to be shown both graphically and in a tabular format Report templates can be saved so that specific information can quickly be referenced Project alarms send email or text messages to project staff for immediate notification of critical conditions With this unique set of features WOData LIVE provides everything needed to effectively manage an environmental monitoring application FONDRIEST COM 15 PURCHASE OR RENT When managing a large or long term scour counter measure project purchasing several scour monitor ing systems is often the most economical option However for short term monitoring projects on a tight budget it may not be practical to purchase the necessary scour monitoring equipment In these situations it is much more prudent to rent real time monitoring systems With several lease duration and extension options available the flexibility of renting scour monitoring systems may still be cost effective for the larger countermeasure applications as well Scour monitoring equipment can be rented instrument by instrument or as an entire system calibrated and ready to deploy on arrival Rental equipment can include sonar hydrologic sensors sondes handheld displays data loggers telemetry stations and web based datacenter access Real time telemetry via radio to shore cellular and sat ellite can also be incorpo
8. cal stream and bridge conditions Before installing any monitoring systems a channel stability assessment should be conducted For most bridges in the US this can be included in the examination required by the National Bridge Inspection Standards This assessment will help determine what if any scour countermeasures are necessary The site and structure should first be examined for scour critical factors such as existing scour channel stability stream and bed type erodible banks and other environmen tal characteristics Short and long term geomorphic changes coupled with bridge design and local site conditions can all affect scour potential at a structure PEKA a dae P am MONITORING SCOUR eh ee ae Ta Ps ara Pena MAT Aa 4 Scour Critical Structures A structure is considered scour critical ifthe abutment s or pier foundation s are coded unstable This classification can be due to current observed scour ora high potential for scour as determined by the assessment Scour critical structures can include more than bridges with existing damage or migrating streams Presently sound bridges with no observable scour but that have a future scour risk due to calculations of 100 year flood conditions are also classified as scour critical Once a structure has been deemed scour critical by a bridge inspection or channel stability assessment the next step is to determine which countermeasures are most
9. ceives a cellular signal With cellular telemetry monitoring stations do not need to be in close proximity nor is a base station required If multiple monitoring stations are required each data logger can send information individually to a central database All the data can then be accessed wirelessly from any computer via the Internet Data loggers may be equipped with cellular modems from different providers including AT amp T Verizon and Sprint For remote applications where radio and cellular telemetry are not feasible satellite telemetry can be used The Iridium communications network main tains a dynamic cross linked constellation of Low Earth Orbiting LEO sat ellites providing coverage all over the world This means that data loggers with an Iridium satellite modem can transmit data in real time from any where on Earth As with cellular networks the data are sent to a central gateway which then transfers the data over the Internet to any project com puter or cell phone Real Time Online Datacenter The easiest way to share and view scour monitoring data is through a web based datacenter An online datacenter offers 24 7 instant access to project data via any web browser Scour monitoring and other data such as water level can be exported into the datacenter directly from the data logger or through the project software This project management service can be password protected or public and allows users access to the c
10. conditions All sensors are cabled through Sealcon gland fittings to ensure protection from the elements NexSens iChart Software is a Windows based program for interfacing to an iSIC data logger or network of data loggers The iChart Setup Device Wizard includes built in drivers and a step by step interface for setting up and con figuring remote monitoring sensors and systems When connected the user can quickly configure sample amp log intervals upload data or troubleshoot communications more Projects are password protected with the ability to configure a public portal or presentation view to share data with the general public Project Administrators have the ability to edit project descriptions and informa tion while users given Collaborator access are limited to data viewing and form entry The Google Maps view shows all project sites on a map with zoom scroll and drag capability Mousing over a site on the map displays the most recent data values and clicking on the site navigates to a display showing the last reading or tabular data that can be downloaded to Excel and sent via email or FTP FieldBooks can be created to store notes recorded during field visits including forms to store calibration data which can be submitted from the WQData LIVE mobile app This eliminates the need for conventional field books while keeping critical project information in a single easy to access location Site photos can even be placed onto Field
11. d value Together they provide bridge scour monitoring sediment transfer studies and much more Pairing st Bridge an innovative and responsive real time scour the compact sensor with a computer or data logger provides a low cost abs 4 monitoring system The Airmar EchoRange SS510 portable hydrographic survey system The EchoRange can also be fixed to II Smart Sensor is a low cost depth sonar with digital a bridge abutment or pillar for unattended monitoring of scour conditions LAN a output for scour and sediment transfer studies The ae iN ae 3 sensor features a robust stainless steel housing with The sensor digitally processes depth and water temperature signals to HEE m communicate data via NMEA 0183 protocol Using NMEA 0183 the sensor easily interfaces with computers or data collection platforms 1 2X 14 NPS threads for convenient mounting The NexSens MAST data logging system arrives fully assembled tested and operational with integrated solar power and a choice of real time radio cellu with a data output rate up to 10 times per second The Echo Range is constructed with a robust stainless steel housing lar and satellite communications Alone real time and has a measurement range from 0 4m to 200m with data are good but with remote data collection 24 7 0 01m resolution access from any computer instant alarm notifica tions and trend tracking the intuitive WQData LIVE takes real time data to t
12. ed intervals With telemetry whether radio cellular or satellite the system can then securely transmit the scour data to the Internet in real time for viewing from any com puter Integrated data logging and telemetry stations are customizable based on bridge scour monitoring needs The integrated system whether mounted on a bridge pier or along the riverbank can connect to and support multiple sensors even when they are mounted on different piers All equipment is powered via a central battery and recharging solar panel system With multiple telemetry options to choose from con tinuous real time data is available from any computer This ensures that the scour conditions are constantly monitored and any control or countermeasures can be implemented immediately if the scour becomes critical MONITORING SCOUR Bridge Piers and Abutments While scour can occur at any underwater structure highway bridges are most likely to be deemed scour critical and require monitoring Scour can be found at both piers and abutments of a bridge If too much sediment is washed away the bridge may collapse fy ft yf ft fy II INSAN D LA YA 4 AN 9 5 1 PA I AL Telemetry Telemetry provides scour monitoring N data in real time by sending the data A X to a central computer or web based datacenter The wireless communication can be radio to shore cellular or satellite based Live Data Scour data can be
13. efficient and cost effective for the location For most sites scour monitoring is considered an effective component of the plan of action if not the sole countermeasure in use Scour critical bridges with no existing scour and a minimum risk may only need a monitoring component as the countermeasure plan of action Older structures with unknown foundations and low level risk may also only have a scour moni toring countermeasure in their plan of action Though a bridge s approved plan of action may only require scour monitoring this does not fix or erase the problem The bridge will remain coded as a scour critical bridge unless other hydraulic or structural countermeasures are also implemented System Location and Deployment Typically scour monitoring stations are mounted directly to the bridge struc ture or near the foundation bed This allows them to monitor high risk areas that are vulnerable to scour While multiple instruments may be impractical on small low traffic structures it may be cost effective to monitor multiple piers for scour on a larger high traffic bridge However due to budget con straints most structures will only have one monitoring station Mounted scour monitoring systems can be set up anywhere that features a supportive foundation Common deployment locations include pole or wall mounting directly to a bridge deck or pier For ease of access the data logger is often mounted on the bridge deck while the senso
14. erm project needs Certifications Fondriest Environmental is a Certihed Repair Center for YSI NexSens amp Fish Sens offering quick turnaround affordable labor rates and personalized service Our knowledgeable technicians are available for phone email and onsite support when the need arises Publications We cover many customer projects in our Environmental Monitor magazine which is updated daily online and printed quarterly We also produce Lake Scientist an interactive online resource providing research articles and news on lake ecology Informational pages on environmental parameters and applications are available in the Measurement Sciences section of our website And FishSens Magazine available online provides anglers boaters and fisheries professionals with the latest fish science news Commitment A commitment to integrity and longstanding customer relations are the standard rather than the exception at Fondriest Environmental We support professionals educators and researchers who continuously work to monitor and protect our global resources by providing them with the products and services needed to face today s environmental challenges Our team of solu tion driven experts has years of field experience and a keen eye for finding the best equipment for each application Contact Information To reach an application specialist please call 888 426 2151 or email customercare fondriest com T D Z U zM
15. gy and organic elements sediment transport can be altered by other exter nal factors The alteration to sediment transport can come from changes in water flow water level weather events and human influence Water flow also called water discharge is the single most important element of sediment transport and streambed erosion The flow of water is respon sible for picking up moving and depositing sediment in a waterway Without flow sediment might remain suspended or settle out but it will not move downstream Flow is required to initiate the transport The equations describing the relationship of water flow and sediment transport are both numerous and elaborate The complexity of sediment transport rates are due to a large number of unknowns e g bed geometry particle size shape and concentration as well as multiple forces acting upon the sediment e g relative inertia turbulent eddies velocity fluctuations in speed and direction Shear stresses in the boundary layer of a sediment bed explain how much force is required for water flow to overcome relative inertia and begin sediment transport through bedload or suspended load When the force of water flow is high enough scour will occur Due to the nature of water flow around a structure greater forces are present through horseshoe and wake vortices These vortices accelerate sediment erosion at the base of the structure While sediment transport and thus scour relies
16. he next level NEXSENS technology WQData LIVE is a web based project management service that allows users 24 7 instant access to data collected from NexSens remote environmen tal data logging amp telemetry systems More than just an online database WOData LIVE offers the ability to generate automated reports configure alarms to notify project personnel when data values exceed threshold limits create FieldBooks to store calibration forms notes and media and much 14 MONITORING SCOUR The iSIC MAST system includes the data logger and solar panel pre mounted to a 2 diameter pole to create a truly plug and play data collec tion and sensor interface platform The system integrates a NexSens iSIC data logger and 20 watt solar power kit all in a compact pre configured package Simply thread the system to any 2 NPT male pipe thread connect the solar panel amp battery wire the sensors and setup a project using iChart software it s that simple The iSIC data logger arrives ready for long term deployment All electron ics are housed in a rugged NEMA 4X enclosure constructed of heavy duty fiberglass The built in 8 5 amp hour sealed lead acid battery provides 12 volt power to the system and the battery is continuously charged using solar power Polymer coated circuit boards sealed connectors corrosion resistant stainless steel hardware and built in lightning protection ensure reliable performance in the harshest
17. ient and cost effective coun termeasures for scour is real time monitoring While monitoring does not prevent or eradicate bridge scour it can provide adequate warning of scour critical conditions Scour monitoring instruments will measure sediment level or bed elevation near a pier or other structure As sediment is eroded away by water flow the elevation decreases and the instrument will measure the sediment level change If a critical level is reached a signal can be transmitted to the necessary personnel for bridge closure While portable scour monitoring instruments exist fixed instruments can provide more frequent data in real time Itis worth noting that no single scour moni toring method can be universally applied to every site regardless of environmental conditions However the three scour monitoring instruments listed here sonar magnetic sliding collar float out device were tested by the NCHRP research team and are in common use MONITORING SCOUR There are three major real time scour monitoring methods in common use These instruments include sonar acoustic transducer magnetic sliding collars and float out devices Any of these devices can be implemented in conjunction with a data logger and real time telemetry system These instru ments all measure elevation changes in the streambed When excessive sedi ment transport occurs such as during a flood event the instruments will indicate the elevation change am
18. ify monitor and improve any highway bridge where scour is or could become critical As scour affects more than just highway bridges it is recommended to monitor other bridges and offshore structures as well These monitoring systems can be used to detect the need for immediate mitigation measures or simply to establish a schedule for structural countermeasures Read the complete FHWA s Stream Stability at Highway Structures HEC 20 http www fhwa dot gov engineering hydraulics pubs hif12004 pdf Read the complete FHWA s Evaluating Scour at Bridges HEC 18 http www fhwa dot gov engineering hydraulics pubs hif12003 pdf Read the complete FHWA s Bridge Scour and Stream Instability Countermeasures Experience Selection and Design Guidance HEC 23 http www fhwa dot gov engineering hydraulics pubs 09111 09111 pdf FONDRIEST ENVIRONMENTAL BRIDGE SCOUR Overview of FHWA Guidance Flood related scour is responsible for the vast majority of bridge failures and closings across the country While most bridges can withstand typical water flows 50 year 100 year and 500 year floods can cause scour critical status or bridge collapse A scour critical status is based on current instabil ity or the potential of instability due to scour To determine the extent of at risk structures the Federal Highway Administration FHWA established the National Bridge Inventory NBI and requires states to report on the con ditions of public bridges Th
19. ing collar systems were thoroughly tested to meet all of the mandatory and desirable criteria While the trialed float out device also met the require ments it was not as thoroughly tested e Capability for installation on or near a bridge pier or abutment e Ability to measure maximum scour depth within an accuracy of 1 ft e Ability to obtain scour depth readings from above water or from a remote site e Operable during storm and flood conditions e Capability to be installed on most existing bridges or during construc tion of new bridges e Capability to operate in a range of flow conditions e Capability to withstand ice and debris e Relatively low cost e Vandal resistant e Operable and maintainable by highway maintenance personnel The NCHRP report stressed that while some methods were more applicable than others no single instrument will be the best option for any and every site The best scour monitoring system should be chosen based on site specific bridge conditions environmental conditions and potential for other influences FONDRIEST COM 13 RECOMMENDED EQUIPMENT While there are a variety of scour monitoring instru ments to choose from some stand out above the rest Fondriest Environmental has selected these products as the best in their field for their accuracy The Airmar EchoRange SS510 Smart Sensor is a digital depth sonar for Welcome Luke Log Oud PR 002022 im dependability an
20. iy m Z lt J O Z IK m SYSTEM CONFIGURATION TOOL Fondriest application specialists will assist with tailoring system configuration and equip ment choices on a site by site basis to ensure reliability and proper data management The questionnaire below can help you get started Once completed this form can be faxed to 937 426 1125 or if completed digitally emailed to customercare fondriest com Contact Information Name Organization Telephone Email Site Conditions Describe the site conditions in a paragraph or two Please include details regarding levels of wind waves and boat traffic experienced in the area 18 MONITORING SCOUR Site Location The location of a monitoring system can affect what equipment platform best suits the conditions Please select in what type of water body the system will reside Ll Lake Ll River Coastal Other Please Specify Number of Instruments While multiple instruments may be impractical on small low traffic structures it may be cost effective to monitor multiple piers for scour on a larger high traffic bridge 1 3 3 5 5 10 Other Please Specify Approximate Depth The mounting hardware and cable lengths used for a deployment depends on the distance to the sea floor An application specialist can develop the best monitoring plan to accommodate the approximate water depth Ll lt 5 ft Ll Between 5 and 25 ft Between
21. le relatively inexpensive and maintenance free these devices do have several drawbacks One such drawback of the float out device is that it will only provide data once the scour has progressed beyond a certain depth and the instrument becomes uncovered However several devices can be buried at multiple depths below the bed to signal scour progress It is recommended to have a level of redundancy when using float outs as once the instrument is buried its functionality cannot be verified These instruments only produce a signal once uncovered and their status cannot be checked in the interim Any instrument failure may result in unsafe condi tions as there will be no warning of critical scour levels SONAR FONDRIEST COM 5 TYPICAL SCOUR MONITORING SYSTEM Scour monitoring is a cost effective and recom mended component of any bridge scour countermea sure strategy A monitoring strategy can be used to detect potential scour problem areas and continually survey current scour progress This is usually done with a monitoring station mounted to the bridge structure with one or multiple sonar sensors providing data To be effective bridge scour should be continuously monitored with the data made available in real time The easiest and most efficient way to do this is with an integrated telemetry system A data logger can support multiple sonar and water level sensors and log scour data from each at pre defin
22. m mended Scour monitoring is particularly important during and after flood events when immediate data can ensure timely control measures A real time system constantly monitors potential problem areas and can alert bridge owners before scour becomes dangerous Several National Coop erative Highway Research Program NCHRP reports substantially expound on the strength of scour monitoring as an effective countermeasure Three of these reports NCHRP Report 396 397a 397b delve into the available scour monitoring instruments and their usefulness based on stream conditions bridge structure and other feasibility factors However scour monitoring even in real time does not erase scour critical status It is intended as a tool for early scour detection improved response time and determining which action should be undertaken to counter scour THE FOUNDATION OF SCOUR Sediment is the collection of organic and inorganic particles that can be moved by water and wind In water quality terms sediment typically refers to mineral based matter such as clay silt sand and gravel that are carried into the water from the local environment The amount of sediment and distance that these particles travel is known as the sediment transport rate Sediment transport and consequently erosion and deposition are dependent on water flow When water flow increases whether by volume or velocity the forces acting on a riverbed also increase D
23. nar sensors and other scour monitoring instruments can connect to a logger directly or through wireless transmissions typi cally float out devices A data logger can also handle additional hydrologic sensors including water level or water flow for more thorough data Telemetry Telemetry or wireless communication is a useful tool for monitoring scour in real time Common telemetry options are cellular and radio though satellite telemetry can be used in more remote locations The deciding factor when determining the most cost effective telemetry option should be the local site conditions and proximity to a project computer All three of these options permit real time updates for local scour conditions Radio telemetry is recommended when all equipment is in close proximity If equipped with a license free spread spectrum radio a data logger can com municate with a shore side or dam mounted radio base station This range may vary depending on the logger and base station used Spread spectrum radio technology may allow a range as far as five miles line of sight or a few hundred feet non line of sight The radio base station serves as a central hub for any compatible data logger in range with the ability to send the collected data to a project computer Cellular telemetry offers more geographic flexibility than radio though it does require a cellular data plan This small additional cost permits data transmissions from anywhere that re
24. ollected data in real time In addition to any streambed elevation information the online interface can provide dynamic area maps overlaid with weather information recent and historical data time series graphs and statistical summaries Visitors can interact with the project maps and view real time monitoring data or scour trends over time But these cloud based datacenters are more than just a pretty face Many can be programmed to send out automated alarm notifications when streambed erosion becomes critical These limits are determined by col lecting background data as per the channel stability assessment or NBIS inspection Once a structural safety limit has been set the data are entered into the online database If sediment erosion reaches the established limit the datacenter can issue an alert text and or email to the bridge owner or appropriate personnel With the availability of real time data and the datacenter s auto alert system timely control procedures can be implemented to close down the bridge or to engage in additional countermeasures when scour becomes critical Alerts are most useful when used in conjunction with additional sensors such as flow or water level instruments The online datacenter can transmit the scour critical alert back to the data logger in response to the flow rate water level or streambed elevation readings Automated responses may include taking more frequent measurements during flood events then re
25. on water flow to move a load downstream this flow rate is variable Water flow is affected not only by the local terrain e g sediment material and slope but by the amount of precipitation received Rainfall influences water flow by increasing the water level and thus volume Precipitation causes water levels to initially rise and then return to previous levels base flow over the course of hours or days The extent to which a rainstorm will influence sediment transport is dependent on the amount and size of sediment available While most periods of precipitation will not have a noticeable effect excessive rain and flooding will Flooding can cause increased sediment transport as the increased flow rate erode additional sediment from both the streambed and embankments In fact most of a waterway s sediment load occurs during flood events While some of this sediment load comes from runoff it is also due to the elevated water level and flow rate Elevated water level creates additional volume in a channel and increases the hydraulic radius cross sectional area of a waterway The increased hydraulic radius drives up the flow rate regardless of whether or not flow is uniform or non uniform Increased flow will add stress on the bed making it more likely for water flow to initiate sediment transport The higher velocity also increases erosion rates as flow overcomes the shear stress of sediment This is why most sediment loss occurs during
26. ontinuously measure and return data They are also easily connected to a telemetry station for real time data transmission These systems are also easy to implement as they do not need to be installed or buried in the riverbed at all However depending on the location and environmental conditions some above surface debris e g ice flows can interfere with the sonar As with any moni toring solution regular maintenance is recommended These instruments can be equipped with one sonar transducer to monitor a specific area or multiple devices to measure elevation changes in a wider range around the pier If a stream migrates shifting the potential scour area it is fairly simple to move the system to the new at risk pier In addition to their appeal as continuously monitoring systems sonar based scour moni toring systems are recommended in deep channels waterways with loose sediment beds and biologically active areas as they are not as susceptible to biofouling in water debris or shifting sediment Sliding collar solutions are comprised of a rod and a ring driven into the riv erbed As the sediment erodes lowering the bed elevation the collar slides down the rod Magnetic triggers in the rod will determine the collar s depth based on its position on the rod While magnetic sliding collars can be automated or manually read they only measure maximum scour depth Manual magnetic sliding collar installations are fairly inexpensive and
27. ount of sediment removed and can send that information to a data logger While other instruments such as tilt sensors sounding rods and piezoelec tric sensors can also be used for monitoring they are not as well known or preferred Tilt sensors measure bridge movement not sediment erosion which requires partial structure failure before action is taken Sounding rods and piezoelectric sensors can provide false or inaccurate measurements Sonar magnetic sliding collars and float out devices on the other hand all measure streambed erosion in areas of potential scour Of all the scour monitoring methods available sonar is the most widely used due to the ease of installation and the wider range of applicable site con ditions In addition sonar instruments provide continuous bed level data while magnetic sliding collars and float out devices only indicate when scour has reached a certain depth Sonar instruments also known as acoustic transducers use sound waves to ping the bottom of a waterway The corresponding echo will indicate depth to the riverbed When the transducer is angled toward an area of potential scour the sensor will measure the level of erosion occurring Most sonar instruments are mounted directly to a pier or substructure of a bridge This indirect measurement method limits interference from debris in the water and makes the instruments easier to maintain Sonar is a popular scour monitoring solution as it can c
28. ponsible sources ae FSC C007943 when your PRSRT STD research US POSTAGE demands AID quality data oavron or PERMIT 860 TAKE YOUR PROJECT TO THE NEXT LEVEL CONTACT A FONDRIEST APPLICATION SPECIALIST 888 426 2151
29. rated A large rental pool also means that most scour monitoring equipment can be shipped same day for quick deployment and emergency situations Just as with Fondriest purchases rental projects have access to a knowledgeable support staff who will provide personalized service before during and after the project Fondriest Environmental Inc 2091 Exchange Court Fairborn OH 45324 tel 888 426 2151 fax 937 426 1125 customercare fondriest com 16 MONITORING SCOUR ABOUT FONDRIEST Company Located in the Lower Great Lakes and Ohio River Valley region Fondriest Environmental is a leading distributor and integrator of equipment for natural resource professionals and outdoor enthusiasts Our team of spe cialists can help customers understand the products they are buying and make the correct decisions out in the field We seek to understand project needs devise a comprehensive solution provide the equipment and know how to implement it and then offer long term project support for whatever needs arise Capabilities We work closely with NexSens Technology a company that specializes in the design and manufacture of real time environmental measurement systems A variety of sensor platform and telemetry options are available to fit the unique needs of each project We can provide complete integrated solutions and support projects from conception to completion An extensive fleet of rental equipment is also available for short t
30. rough the NBI structurally deficient or scour critical bridges must be iden tified and a plan of action POA for monitoring and scour countermeasures must be developed Monitoring plans are further outlined and discussed in the FHWAS three set guidance manuals These manuals are published in the Hydraulic Engineering Circular HEC and are intended to be referenced in sequence The first manual Stream Stability at Highway Structures HEC 20 assists in initial data collection to assess water channel classification and channel instability The second manual Evaluating Scour at Bridges HEC 18 estab lishes procedures for hydrologic and hydraulic analysis of waterways This manual further evaluates the existing risk and potential scour at the struc ture The final guidance manual FHWA s Bridge Scour and Stream Instability Countermeasures HEC 23 provides options for monitoring and combating bridge scour HEC 23 details the need for a monitoring strategy preferably in real time within the countermeasure proposal In compliance with the NBI and often in conjunction with the U S Geological Survey state DOTs can establish a thorough POA for scour critical bridges within their boundaries The POA is developed for each bridge individually detailing the best countermeasure methods to monitor and remedy current bridge scour as well as to prevent or slow its future expansion When implementing a POA a real time monitoring solution is reco
31. rs are mounted below The system can include a locking stainless steel enclosure to protect the data logger and telemetry modem from harsh weather and vandalism Connected sensors run from the station down the pier into or over the water Sonar sensors are mounted out from the pier face while magnetic sliding collars are driven into the sediment at the base of the pier Float out devices are not connected at all but are buried near the bridge foundation These devices should still have a signal receiving unit on the bridge deck or mounted nearby to log when the instrument becomes uncovered Selecting the Instrumentation Scour monitoring as a countermeasure is used to survey scour progress and identify potential scour before it becomes a hazard Based on environmental conditions including river type flow rate and bed material one instrument may be better suited than others Whether or not the monitoring counter measure is intended as a short or long term solution will also play a role in instrument selection If conditions and budget allow for it multiple instru ments may be used to cover all situations as well as to provide data redun dancy and quality assurance The chart below can be consulted to assist in determining which instrument would be best suited to a structure based on monitoring needs and river conditions Some plans of action may require additional monitoring beyond scour and sediment erosion Adding other hydraulic variable
32. s more raw elevation data for more accurate sediment transportation models Real time alerts by text or email also ensure a faster response time when adverse conditions arise meee Data Logger As the name implies a data logger is an instrument that stores data In envi ronmental monitoring applications data loggers can be used not only to collect data from sensors and monitoring instruments but to control log intervals and transmit data to a central location in real time While some scour monitoring instruments have the ability to log their own data a separate dedicated data logger can gather all data from any and all attached sensors ensuring that no data are lost If telemetry wireless communication is available the logger can remotely control measurement intervals and transmit the collected data to a central project computer Data loggers with telemetry technology can provide real time scour data and remote access via a cellular modem radio transmission or satellite modem Most scour monitoring systems use a mounted data logger on the bridge deck or other structure The equipment is powered by an external battery often housed in the same enclosure with a recharging solar panel For bridge mounted systems near an AC power source an AC converter can be used Data loggers can be configured with a number of sensor ports for con nection to industry standard digital and analog interfaces including RS 485 SDI 12 or 0 2 5 VDC So
33. suming regular log intervals when water levels return to normal East River Buoy 01 2 24 Friday October 3 wadatalive nexsens com WQData LIVE Alert Scour Potential Ihe distance lo bollom al Pier 3 has dropped below 4 Il FONDRIEST COM 11 QUALITY ASSURANCE To ensure and maintain structure safety accurate data are important Accurate scour information can help prevent structure failure by keeping bridge owners and other personnel aware of scour criti cal conditions Ideally all equipment should meet or exceed the NCHRP s desirable criteria for sensor quality and robustness In addition best practice recommends regular maintenance of sensors and equipment to prevent damage and interference from debris or shifting sediment conditions If a budget allows it redundancy is also recommended to confirm that all sensors are operating within specifications The majority of fixed scour monitoring systems require regular mainte nance Whether the main instrument in use is a sonar sensor or a magnetic sliding collar the equipment will need to be checked for functionality and to remove debris While most scour monitoring instruments do not require calibration the quality of data can be affected by external influences partic ularly debris The exception is float out devices as they cannot be accessed while they are installed For sonar based monitoring systems the sensor face should be kept clean and the se
34. tup should be regularly checked to prevent damage due to van dalism or above water debris Magnetic sliding collar systems are harder to maintain as they are below the surface of the water However it is extremely important to inspect the equipment regularly particularly in waters with risk of biological growth algae or barnacles Biofouling can interfere with readings and damage the equipment if not removed Data loggers should also be included in the maintentence check The enclosure dessicant pack should be replaced regularly to prevent moisture damage to the electronics and the battery may need to be replaced every three to five years Ideally a scour monitoring system should be installed in such a way as to protect the sensors and instruments from damage This can include a deployment pipe or other robust material to guard the equipment from debris For structure mounted systems or data loggers a locked enclosure can help deter vandalism For greater details regarding maintenance requirements the manufacturer s user manual and the HEC guidelines should be referenced The National Cooperative Highway Research Program NCHRP developed four mandatory criteria and six desirable criteria for any scour monitoring system The required benchmarks were established as necessary for a suc cessful monitoring application while the desirable conditions will assist in effectiveness and efficiency During the NCHRP s testing both sonar and slid
35. uring high flow events such as floods and snow melt the amount of sediment picked up by the higher flow rate increases increasing the sediment transport rate and causing erosion While sediment transport and deposi tion are an important part of most aquatic ecosystems the constant erosion can pose a risk to man made structures Scour riverbed erosion at a structure is a conse guence of excessive sediment transport When sedi ment erosion occurs at the base of a bridge pier or other structure it can cause safety concerns due to structural compromises MONITORING SCOUR Sediment transport is the movement of organic and inorganic particles by water In general as flow speeds increase so does the potential for sediment transport Water flow can be strong enough to suspend particles in the water column as they move downstream or simply push them along the bottom ofa waterway Transported sediment may include mineral matter chemicals and pollutants and organic material While much of the sediment load will come from runoff and bank erosion loose sediment on the bottom of a streambed can easily be picked up and carried downstream Due to the tur bulent eddies that exist at an underwater structure this streambed erosion is more likely to occur at the base of a pier or abutment Sediment transport is not constant In fact it is constantly subject to change In addition to the changes in sediment load due to geology geomorpholo
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