Monitoring Scour Critical Bridges (2009)

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13 OVERVIEW OF SURVEY AND LITERATURE SEARCH This overview of bridges with fixed scour monitoring systems includes data from the respondents of the survey, as well as information obtained from the literature search and other sources. This study identified 32 states and the District of Columbia that have installed fixed scour monitoring systems on one or more of their highway bridges. This includes systems that are currently active, those that are no longer in service, and states with plans to install monitoring systems. These states are listed and shown on a map of the United States in Figure 17. The bridges that have been identified by survey responses and through the literature search are listed in Tables 2 and 3, respectively. Additional information on fixed instrumentation and scour critical statistics for all the states, the District of Columbia, and Puerto Rico can be found in Appendix D. A total of 81 completed scour monitoring surveys were received and these represented 37 different states. Several states completed surveys for more than one bridge site, includ- ing different districts and agencies. A list of the respondents can be found in Appendix B. Of the respondents, 29 reported using fixed or portable instrumentation for scour monitoring, and 21 stated they did not. The group that used instrumen- tation included 25 that stated they used fixed instrumenta- tion and 14 that said they used portable instrumentation. Completed surveys were received from a total of 56 sample bridge sites that used fixed instrumentation, and these were from 19 different states. The states that use fixed scour monitoring instrumenta- tion were asked about their general scour monitoring expe- rience and to complete specific detailed questions on at least one sample bridge site. An abridged survey was sent to sev- eral states that had several bridges with fixed scour instru- mentation. They were also asked to provide additional, less detailed information on other bridge sites they are moni- toring. The following states submitted completed full surveys for multiple bridge sites: Alaska, Florida, Georgia, Hawaii, New Jersey, and New York. Caltrans submitted the abridged survey for seven additional bridge sites. The majority of the sample bridges (51) were state owned and maintained by their DOTs. Five bridges were owned by a city, county, or other agencies. The respondents for the 56 monitored bridge sites where surveys were completed reported a wide range of conditions. Table 4 includes a list of these bridges with statistics on each location. The average daily traffic (ADT) for the monitored bridges ranged from 100 to 175,000 vehicles per day. The mean ADT was 21,635, and the median was 8,190 vehicles per day. The total length of the bridges varied from small to long span bridges. The smallest bridge was 12 m (41 ft) long, whereas the longest was 3,921 m (12,865 ft) in length. The mean bridge length was 302 m (992 ft), and the median was 120 m (394 ft). The bridges being monitored were constructed between 1901 and 1988. The mean and median years were 1959 and 1963, respectively. The scour monitors reported in these surveys had been or were scheduled to be installed between 1991 and 2008. The majority of owners reported a history of scour and a scour critical rating for the bridges being monitored. Sixty percent of the bridges being monitored were on pile foun- dations, 35% were on spread footings, and drilled shafts, unknown foundations, and other were each 2%. The foun- dation depths were reported to be 67% as-built depths, 22% design depths, and 11% unknown. Borings and/or soil and rock data were available for all but six of the bridge sites. SITE-SPECIFIC FACTORS AND THE SELECTION PROCESS When deciding which fixed scour monitoring system to use, many factors need to be considered. These considerations range from waterway characteristics to bridge geometry to soil conditions. The decision-making process requires the multi-disciplinary effort of hydraulic, structural, and geotechnical engineers. FHWA HEC-23 (Lagasse et al. 2001a) contains a table to aid in the selection of a fixed scour moni- toring system. It includes both advantages and disadvantages of various conditions as they pertain to fixed scour monitoring. Table 5 is a matrix that summarizes some of these site- specific factors from the surveys. This matrix highlights some of the factors that could be considered when deciding which type of fixed scour monitoring instruments work best for your site. The following is a discussion of the conditions that affect the selection of an appropriate fixed scour monitoring system. The final chapter of this report contains a discussion of best practices and includes additional selection tables based on the information obtained in this study. Chapter eight includes CHAPTER THREE OVERVIEW OF BRIDGES BEING MONITORED

two additional tables that can be used for the selection of fixed instrumentation and are based on the survey respondents and literature search. Bridge Geometry and Size The bridge owners reported that 89% of the structures moni- tored with fixed instruments were piers. Abutments were 3% and others were 8%. Others included bulkhead and down- stream sheetpile protection. Complex pier geometry can make it difficult to mount equipment directly onto the structure. Protrusions from footings or steel sheeting can block monitor readings. As-built bridge plans or measurements from divers can provide important information for the design of the components of the scour monitors. In the case of sonar scour monitors, adjustable mounting brackets have been developed for flexibility during the installation and to allow the moni- tors to take readings beyond the footing or any steel sheeting. Sample plans for a tripod telescopic bracket can be found in Appendix G. Other important considerations in the selection of the scour monitor include bridge height off the water and foundation type. Waterway Type, Flow Habit, and Water Depth Understanding the waterway characteristics will enable the bridge owner to determine what type of information is needed 14 and which monitors would work best at the site. The type of waterway, tidal or riverine, is an important consideration. Both flood and ebb conditions need to be taken into account in the tidal environment. The instrumented bridge sites included 78% riverine and 22% tidal environments. Riverine waterways often contain debris flows that can prevent the system from taking readings and/or damage the instrumenta- tion. In tidal waters, scour monitors can be placed on both sides of the bridge to monitor the scour conditions owing to incoming and outgoing tides. The flow habit is another important factor to consider. With ephemeral and intermittent waterways, the streambed is dry some or most of the time. Perennial waterways always have some flow. Both types of conditions affect the type of installation procedures that can be used to place a monitoring system at the site. The bridge owner also needs to assess whether continuous monitoring is needed and practical. Certain monitors such as sonars and magnetic sliding col- lars yield a continuous set of data. Other types of monitors such as float-out devices are activated only when certain scour depths are reached. Sixteen percent of the survey respondents reported ephemeral and intermittent conditions at their bridge sites and used a combination of continuous and non-continuous monitors. Eight-four percent of the bridges were in perennial or perennial but flashy conditions, and all but one of those bridge sites employed continuous monitors only. FIGURE 17 States with fixed scour monitoring installations.

15 State Bridge Type(s) of Fixed Scour Monitors Date o f Installation Waterw ay Type Flow Habit Waterw ay Depth Alabam a US-82 1 Float-O u t N /A Riverine Perenni al 51–75 f t Alas k a Tanana River Bridge No. 202 1 Sona r 200 3 Riverine Perenni al 10–30 f t Kashwitna River Bridge No. 212 1 Sona r 200 2 Riverine Perennial <10 ft Montana Creek Bridge No. 215 2 Sonars 200 2 Riverine Perennial <10 ft Sheridan Glacier No. 3 Bridge N o. 230 1 Sona r 200 2 Riverine Perennial <10 ft Copper Delta Bridge No. 339 1 Sona r 200 2 Riverine Perennial <10 ft Copper Delta Bridge No. 340 1 Sona r 200 2 Riverine Perennial <10 ft Copper Delta Bridge No. 342 8 Sonars 200 5 Riverine Perenni al 10–30 f t Salcha River Bridge No. 527 1 Sona r 200 2 Riverine Perennial <10 ft Knik River Bridge No. 539 1 Sona r 200 2 Riverine Perenni al 10–30 f t Slana Slough Bridge No. 654 1 Sona r 200 5 Riverine Perennial <10 ft Slana Slough Bridge No. 655 1 Sona r 200 4 Riverine Perennial <10 ft Mabel Slough Bridge No. 656 1 Sona r 200 2 Riverine Perennial <10 ft Tok River Bridge No. 663 2 Sonars 200 4 Riverine Perennial <10 ft Kasilof River Bridge No. 670 2 Sonars 200 5 Riverine Perennial <10 ft Kenai River at Soldotna No. 671 1 Sona r 200 5 Riverine Perennial <10 ft Eagle River Bridge No. 734 1 Sonar, Ultrasonic Piezoelectric Fil m 200 5 Riverine Perenni al 10–30 f t Red Cloud River Bridge No. 983 1 Sona r 200 5 Riverine Perenni al 10–30 f t Glacier Creek Bridge No. 999 1 Sona r 200 5 Riverine Perenni al 10–30 f t N enana River at Wi ndy Bridge N o. 1243 1 Sona r 200 5 Riverine Perenni al 10–30 f t Lowe River Bridge No. 1383 1 Sona r 200 2 Riverine Perennial <10 ft Arkansas Red River at Fulton 1 Sonar; 1 Ultrasonic Distance; cam er a 200 6 Riverine Perenni al 10–30 f t Califor ni a Toom es Cree k 5 Tilt Sensors 200 2 Riverine Ephem eral <10 ft St. Helena Cree k 1 Magnetic Sliding Collar, 1 Tilt Senso r 200 2 Riverine Perennial but Flash y <10 ft Merced Rive r 2 Sonars 199 7 Riverine Perennial <10 ft SR-101 Bridge over the Salinas Rive r Magnetic Sliding Collars, Float-Outs 0 Riverine Ephem eral 10–30 f t Cholam e Cree k 6 Float-Outs, 1 Tilt Senso r 199 9 Riverine Ephem eral <10 ft Tick Canyon Wash 16 Float-Out s 199 9 Riverine Interm itte n t <10 ft San Mateo Creek—L / R 8 Tilt Sensors 200 1 Riverine Perennial <10 ft San Gorgonio Rive r 2 MSC; 6 Circuit Cables a t Levee 200 5 Riverine Perennial but Flash y 10–30 f t Santa Clara Rive r 1 Sonar, 16 Tilt Sensors, 32 Float-Outs 200 0 Riverine Perennial but Flash y <10 ft Florid a SR-105 and SR-A 1 A 8 Sonars 200 2 Tidal Interm itte n t 10–30 f t John's Pass Bridge 2 Sonars 199 7 Tidal Interm itte n t 31–50 f t TABLE 2 BRIDGES WITH FIXED SCOUR MONITORS I Information from Synthesis Surveys (continued on next page)

16 State Bridge Type(s) of Fixed Scour Monitors Date of Installation Waterway Type Flow Habit Waterway Depth Georgia Otis Redding Bridge 6 Sonars 2001 Riverine None <10 ft Georgia Highway 384 over Chattahoochee River 4 Sonars 2001 Riverine None <10 ft US Highway 27 over Flint River 6 Sonars 2001 Riverine None 10–30 ft US Highway 17 over Darien River 3 Sonars 2001 Tidal None 10–30 ft Hawaii Kaelepulu Bridge, Oahu 2 Magnetic Sliding Collars 2002 Tidal Perennial but Flashy <10 ft Kahaluu Bridge, Oahu 1 Sonar 2003 Tidal Perennial <10 ft Indiana US-52 over Wabash River and SR-43 1 Sonar, 1 Magnetic Sliding Collar 1997 Riverine Perennial 10–30 ft Kansas Amelia Earhart Bridge (US-59) 2 Sonars 2000 Riverine Perennial 76–100 ft Maryland / Virginia / Washington DC Woodrow Wilson Memorial Bridge (US-495) 5 Sonars 1999 Tidal Perennial 31–50 ft Minnesota TH 16 over Root River, Rushford Village 1993 Riverine Perennial but Flashy <10 ft Nevada SR-159 over Red Rock Wash 2 Sonars, 2 Float-Outs 1997 Riverine Intermittent <10 ft North Carolina Herbert C. Bonner (NC-12) 4 Sonars 1992 Tidal Perennial 51–75 ft New Jersey Route 35 over Matawan Creek 1 Sonar, 1 Magnetic Sliding Collar 1999 Tidal Intermittent 10–30 ft Route 46 over Passiac River 1 Sonar, 1 Magnetic Sliding Collar 2000 Riverine None 10–30 ft New York Wantagh Parkway over Goose Creek 4 Sonars 1998 Tidal Perennial 10–30 ft Robert Moses Causeway over Fire Island Inlet 13 Sonars 2001 Tidal Perennial 31–50 ft Route 262 over Black Creek 1 Brisco 1993 Riverine Perennial <10 ft Wantagh Parkway over Sloop Channel 10 Sonars 1998 Tidal Perennial 10–30 ft NYS Thruway over Cattaraugus Creek (US-90) 6 Magnetic Sliding Collars 1999 Riverine Perennial but Flashy 10–30 ft Willis Avenue Bridge over Harlem River 15 Sonars 2007 Tidal Perennial 31–50 ft Texas FM 1157 Bridge over Mustang Creek Sonars 1998 Riverine Perennial <10 ft Vermont Vt Route 5 over White River 2 Time Domain Reflectometers 1997; 2001 Riverine Perennial but Flashy 76–100 ft Washington Klineline Bridge #1 2 Sonars; 2 Tilt Sensors 2006 Riverine Perennial <100 ft TABLE 2 (continued)

17 State Bridge Type(s) of Fixed Scour Monitors Date of Installation Arizona I-10 over Gila River, Bridge No. 0185 12 Float-Outs, 1 Sonar 1997–98 I-17 over Verde River, Bridge No. 00505 4 Float-Outs, 1 Sonar 1997–98 Franconia 3 Float-Outs, 1 Brisco 1997–98 San Pedro River, Bridge No. 1530 1 Sonar 1997–98 Float-Outs 1997–98 California Colorado River 2 Magnetic Sliding Collars Santa Rosa River 6 Float-Outs, 2 Tilt Sensors Putah River 4 Tilt Sensors Kidder Creek 3 Float-Outs Scott River 3 Float-Outs Temecula Creek 9 Float-Outs Eel River 5 Tilt Sensors Colorado Orchard Bridge over South Platte River 1 Manual Sliding Collar, 1 Sonar South Platte River Bridge 1 Magnetic Sliding Collar, 1 Sonar Connecticut Mystic River Bridge Brisco Delaware SR-1 over Indian River Inlet 2 Sonars and Tilt Meters 2007–08 Florida Nassau Sound Bridge 1 Magnetic Sliding Collar Indiana SR-26 Bridge over Wildcat Creek 1 Sonar, 1 Magnetic Sliding Collar 1997 Iowa US-34 Mississippi River Bridge 2 Briscos 1991 Maine 1 Magnetic Sliding Collar Michigan US-31 over the Muskegon River 1 Manual Sliding Collar Minnesota US-14 over Straight River near Owatonna 1 Manual Sliding Collar 1993 TH 76 over Root River, Houston 1 Manual Sliding Collar 1993 New Hampshire Brisco Nevada I-15 over California Wash, Bridge No. 839S 3 Float-Outs, 1 Sonar 1997–98 I-15 over Toquop Wash, Bridge No. 571N 3 Float-Outs, 1 Sonar 1997–98 West Charleston Blvd at Red Rocks, Bridge No. 1805 3 Float-Outs, 1 Sonar 1997–98 US-95 over Piute Wash, Bridge No. 420 8 Float-Outs, 1 Sonar 1997–98 Virgin River 24 Float-Outs—to be installed TBD TABLE 3 BRIDGES WITH FIXED SCOUR MONITORS II Information from Literature Search and Other Sources (continued on next page)

18 State Bridge Type(s) of Fixed Scour Monitors Date o f Installation N ew Mexico Bernado Bridge over the Ri o Grande Magnetic Sliding Collars San Antonio Bridge over the Ri o Grande Sonar s N ew Yor k State Rte 30/145 over Schohari e Cree k 1 Manual Sliding Colla r 199 4 US-418 Bridge over the Hudson Riv e r 1 Sona r 199 4 Oregon US-Hwy 101 over Alsea Ba y Sonars early 90s Highway 92 over Wallowa Rive r Sonar s Interstate 84 over Sandy Rive r Sonar s Hwy 226 over Crabtree Creek Sonar s Hwy 22 at Mill Creek Misc. site Interstate 5 at Little Mudd y Cree k Misc. site Highway 101 Test site for new met hods Sandy River near Troutdale 1 Piezoelectric Film Rhode Island Westerly Bridge 4 Magnetic Sliding Collars Jamestown–Verrazzano 4 Sonars Texas US Highway 380 Bridge/Doubl e Mountain Fork/Brazos Rive r 1 Magnetic Sliding Colla r US Highway 59 Bridge over th e Brazos Riv e r 1 Sona r US Highway 59 Bridge over th e Trinity Riv e r 1 Sona r US Highway 90 Bridge ove r Trinity Riv e r 1 Sona r Verm on t Bridge Street Bridge over White River Junctio n 1 Brisco 199 1 Route 5 Bridge over White Rive r 1 Brisco 1960s Wiscons in 1 Magnetic Sliding Colla r 1 Magnetic Sliding Colla r County Highway B Bridge, Crawfish Rive r 2 Manual wire-weight gages 200 2 Balsam Road Bridge, Big Ea u Pleine Rive r 2 Sonars 199 8 Wisconsin Highway 35 Bridge , Tank Cree k 1 Sona r 1999 TABLE 3 (continued)

(continued on next page) State Bridge Nam e Bridge Identification Num ber (BIN) Type(s) of Fixed Scour Monitors ADT Year Bui l t Yea r Rebui l t NBI S Item 113 Foundation Type Known Foundation Depth Alabam a US-82 0 1 Float-O u t 9,000 196 2 N /A 345 1,13 3 N /A Pile s A s- b uilt depths Alas k a Tanana River Bridge No . 202 202 1 Sona r 0 196 5 0 398 1,30 5 0 Kashwitna River Bridge N o. 212 212 1 Sona r 2,359 196 2 0 65 213 7 Piles & Spr Ftg As - b uilt depths Montana Creek Bridge N o. 215 215 2 Sonars 0 196 2 0 43 140 0 Sheridan Glacier No. 3 Bridge No. 230 230 1 Sona r 0 196 8 0 61 201 0 Copper Delta Bridge No. 339 1 Sona r 0 197 7 N /A 122 401 7 Pile s As - b uilt depths Copper Delta Bridge No. 340 340 1 Sona r 0 197 7 N /A 73 241 Pile s As - b uilt depths Copper Delta Bridge No. 342 342 8 Sonars 0 1977 1988 269 881 7 Pile s As - b uilt depths Salcha River Bridge No . 527 527 1 Sona r 0 1967 154 504 0 Knik River Bridge No . 539 539 1 Sona r 3,407 197 5 N /A 154 506 7 Pile s As - b uilt depths Slana Slough Bridge No . 654 654 1 Sona r 400 197 9 0 47 153 0 Slana Slough Bridge No . 655 655 1 Sona r 400 1979 200 6 1 2 4 1 0 Mabel Slough Bridge No . 656 656 1 Sona r 400 197 9 0 12 41 0 Tok River Bridge No. 663 663 2 Sonars 0 196 9 0 73 241 0 Kasilof River Bridge No . 670 670 2 Sonars 4,610 196 5 0 87 284 0 Kenai River at Soldotn a N o. 671 671 1 Sona r 0 0 0 120 394 0 Eagle River Bridge No . 734 734 1 Sonar, Ultrasonic Piezoelectric Film 351 195 9 0 64 211 7 Spread footing As - b uilt depths Red Cloud River Bridge N o. 983 983 1 Sona r 100 0 19 63 0 Glacier Creek Bridge No. 999 999 1 Sona r 3,71 1 0 68 222 7 Spread footing As - b uilt depths N enana River at Wi nd y Bridge No. 1243 124 3 1 Sona r 1,912 197 3 0 119 389 0 Lowe River Bridge No . 1383 138 3 1 Sona r 461 197 8 0 92 303 0 Bridge Length (m ) (ft) TABLE 4 BRIDGE SPECIFIC DATA Sample Set of 56 Surveyed Bridges with Fixed Scour Monitors

State Bridge Name Bridge Identification Number (BIN) Type(s) of Fixed Scour Monitors ADT Year Built Year Rebuilt NBIS Item 113 Foundation Type Known Foundation Depth Arkansas Red River at Fulton 3981 1 Sonar; 1 Ultrasonic Distance; Camera 20,900 1959 394 1,294 3 Spread footing As-built depths California Toomes Creek 08-0005 5 Tilt Sensors 8,190 1917 1952 117 385 St. Helena Creek 14-0016 1 Magnetic Sliding Collar, 1 Tilt Sensor 7,030 1934 57 187 Merced River 39-0071 2 Sonars 2,230 1953 144 473 SR-101 Bridge over the Salinas River 44-0002 L/R Magnetic Sliding Collars, Float-Outs 12,350 1939 1960 (L) All 1999 384 1,260 Cholame Creek 49-0095 6 Float-Outs, 1 Tilt Sensor 5,370 1959 56 184 Tick Canyon Wash 53-1547 16 Float-Outs 89,000 1963 35 114 San Mateo Creek—L/R 57-0001 L/R 8 Tilt Sensors 22,500 1968 154 506 San Gorgonio River 56 0003 1 MSC; 6 Circuit Cables at Levee 86,000 1940 73 239 8 Spread footing As-built depths Santa Clara River 1 Sonar, 16 Tilt Sensors, 32 Float- Outs 1930 1965 558 1,830 3 Piles As-built depths Florida SR-105 & SR A1A 720062 8 Sonars 1949 N /A 37 120 5 Piles As-built depths John's Pass Bridge 150076 2 Sonars 1971 N /A 253 830 3 Piles As-built depths Georgia Otis Redding Bridge N /A 6 Sonars Spread footing Design depths Georgia Highway 384 over Chattahoochee River N /A 4 Sonars Piles Design depths US Highway 27 over Flint River N /A 6 Sonars Spread footing Design depths US Highway 17 over Darien River N /A 3 Sonars Piles Design depths Hawaii Kaelepulu Bridge, Oahu 3.00083E+12 2 Magnetic Sliding Collars 1960 61 200 Spread footing Unknown Kahaluu Bridge, Oahu 1 Sonar 97 318 Spread footing Unknown Indiana US-52 over Wabash River and SR-43 21480 1 Sonar, 1 Magnetic Sliding Collar 16,498 1969 1984 305 1,002 8 Piles Design depths Kansas Amelia Earhart Bridge (US-59) B0003-0013 2 Sonars 8,960 1938 N /A 762 2,500 5 Piles Design depths Bridge Length (m ) (ft) TABLE 4 (continued) (continued on next page)

State Bridge Name Bridge Identification Number (BIN) Type(s) of Fixed Scour Monitors ADT Year Built Year Rebuilt NBIS Item 113 Foundation Type Known Foundation Depth Maryland/Virgina Woodrow Wilson Memorial Bridge (US 495) 5 Sonars 175,000 1961 2006 1,798 5,900 5 Piles As-built depths Minnesota TH 16 over Root River, Rushford Village 23015 1 Magnetic Sliding Collar 2,000 1988 219 718 8 Piles As-built depths Nevada SR-159 over Red Rock Wash B1805 2 Sonars, 2 Float- Outs 2,650 1985 N/A 61 200 5 Piles As-built depths North Carolina Herbert C. Bonner (NC- 12) 270011 4 Sonars 5,100 1962 N/A 3,921 12,865 3 Piles As-built depths New Jersey Route 35 over Matawan Creek 1313-161, 162 1 Sonar, 1 Magnetic Sliding Collar 30,000 1986 137 450 Piles Unknown Route 46 over Passiac River 1607-168 1 Sonar, 1 Magnetic Sliding Collar 70,000 1920 137 450 Unknown Unknown New York Wantagh Parkway over Goose Creek 1058509 4 Sonars 12,900 1930 1998 164 537 3 Piles Design depths Robert Moses Causeway over Fire Island Inlet 1058770 13 Sonars 16,809 1966 2001 1,290 4,233 6 Piles As-built depths Route 262 over Black Creek 1 Brisco N/A 1949 1981 23 75 3 Spread footing As-built depths Wantagh Parkway over Sloop Channel 1058499 10 Sonars 12,900 1930 1999 226 740 3 Piles Design depths NYS Thruway over Cattaraugus Creek (US 90) 5511570 6 Magnetic Sliding Collars 31,730 1954 1992 203 667 7 Piles As-built depths Willis Avenue Bridge over Harlem River 2-24005-9A/B 15 Sonars 75,000 1901 2007 979 3,212 Design depths FM 1157 Bridge over Mustang Creek N/A 4 Sonars N/A 1958 Spread footing Unknown Verm Texas ont Vt Route 5 over White River N/A 2 Time Domain Reflectometers 1966 337 1,105 Piles As-built depths Washington Klineline Bridge #1 8356100 2 Sonars, 2 Tilt Sensors 17,000 1929 1954 40 132 2 Spread footing Design depths Median 8,190 1963 1992 120 394 Mean 21,635 1959 1987 302 992 Bridge Length (m) (ft) TABLE 4 (continued)

22 Sonar Sensors Magneti c Sliding Collars Tilt Sensors Float-Out Devices Piezoelectric Film Ti me Do ma in Reflectom eter s T ota l Bridge Geom etry Substructure Monitored Abutm en t 1 2 3 Pie r 47 10 3 2 2 1 65 Foundation Type Pile 33 4 2 2 1 42 Spread Footings 19 3 1 1 24 Drilled Shafts 0 Unknow n 0 Othe r 0 Waterw ay Characteristic s Waterw ay Type Tida l 11 1 12 Riverine 37 8 3 3 2 1 54 Flow Habi t Ephem eral 24 1 25 Interm itte n t 17 1 1 1 20 Perennial but flash y 4 4 1 1 1 11 Perennial 37 3 1 1 42 Water Dept h <10 f t (<3 m) 19 4 2 2 27 10–30 f t (3.1–9.1 m) 17 5 1 1 24 31–50 f t (9.2–15.2 m) 4 4 51–75 f t (15.3–22.9 m) 1 1 2 76–100 f t (23–30.5 m) 0 Soil Conditions Clay 9 2 1 2 14 Fine Sand/Sil t 20 7 1 1 29 Coarse/Medium San d 35 4 4 2 1 46 Grav e l 25 5 4 1 35 Cobbles 22 6 1 29 Organic s 2 1 1 4 Ripra p 6 1 1 8 Extrem e Conditions Debri s 34 6 3 1 44 Extrem e tem peratures 1 1 2 Sedim ent loading 29 5 2 36 Ice flows 25 3 1 29 Air entrainm en t 1 1 High velocity flow s 35 2 2 1 40 Pow er Source (for mo nitoring system ) Sola r 40 3 2 2 47 Co mme rcia l 9 2 2 2 1 Back-up battery 23 Access (to monitoring system) Security clearance Lane closures 8 1 1 Boat 30 3 1 Keys to doors/gates 21 1 2 1 Data Retrieval (from mo nitoring system s) Locally 24 4 Telephone 13 3 3 1 Cellular 5 1 1 1 Satellite 26 16 23 0 10 34 25 28 20 8 26 Installation Experience by State AK, AR, CA, FL, GA, HI, IN, KS, MD, NC, N J, NV, NY, TX, VA, WA CA, HI, IN, MN, N J, NY CA, WA AL, CA, N V AL VT FIXED SCOUR MONITORING SYSTEM2 SITE CONDITIONS 1. Results based on 56 complete surveys that indicated the use of fixed scour monitoring systems at specific bridge sites. Additional bridge sites were reported but not in full detail. See Tables 2 and 3 for a complete list of reported bridge sites with fixed scour monitoring instrumentation. 2. Vibration sensors and buried/driven rods were also in the survey. However, none of the survey respondents reported using these fixed scour monitoring systems. Notes: Some bridge sites have multiple types of fixed scour devices in one scour monitoring system. TABLE 5 BRIDGE SITES WITH FIXED SCOUR MONITORING SYSTEMS1

23 Water depth can be another limiting factor. In deeper waterways it can be expensive and difficult to bury monitors in the streambed. Driven rods can also not be practical in deeper channels owing to the long, unsupported length of the rods. Soil Conditions The type of soil being monitored is important. Clays tend to erode at a slower rate than sands. Clays can reach their max- imum scour depths after numerous events, whereas sands can reach the maximum scour depths in one event. Sands are also more prone to infilling of a scour hole after an event. Infill is often less dense and does not have the same capacity as the original soil. Infilling is difficult to detect through diving inspections or occasional portable field measurements. The scour hole usually fills in within a short period of time following a storm event. A majority of the survey respon- dents reported sand as the predominant soil and used fixed scour monitors with continuous data recording capabilities (Figure 18). The type of soil present is also a good indicator of where monitors could be placed with relation to the structure. In clays, the greatest scour occurs behind the pier as it faces the flow. In sands, the greatest scour is usually located on the upstream face of the pier. A scour monitor should be placed at a location that will allow the engineer to decide if the bridge foundation is becoming dangerously close to failure. With this concern in mind it becomes critical to place the scour monitor at the location of the potential deepest scour depth around the foundation. This location cannot be obvious and deciding where to place the scour monitor should be studied carefully on a case- by-case basis while taking advantage of existing knowledge. In sands, it is likely that the location extends fairly broadly in front and to the side of the pier; in clays, that is not necessarily the case. Laboratory experiments indicate that in clay the scour hole around a cylindrical pier can be non-existent in front of the pier, although it is significant on the side of the pier where the mean shear stress is maximum and behind the pier where the turbulence intensity is high (Briaud et al. 2003). Placing the scour monitor in front of the pier in this case would indicate no scour when the scour hole would be significant around the sides and in the back (Figure 19). The shape of the pier is also a factor. Long rectangular piers develop a scour hole at the front of the pier but little scour behind the pier because the flow is streamlined by the time it gets to the back. A second problem associated with locating the scour mon- itor is that the scour hole around the bridge support cannot be the same depth all around the pier. Considering all factors, it appears that the best place for placing the monitor is to the side of the pier immediately behind the front edge. This can also help in reducing the impact of debris. Nonetheless, it is important to consider each case independently. 0 5 10 15 20 25 30 35 40 45 N um be r of In st al la tio ns No. 12 24 40 33 22 5 1 8 4 Clay Fine Sand to Silt Coarse to Med. Sand Gravel Cobbles Organics Concrete Riprap Rock FIGURE 18 Soil conditions at scour monitoring locations. FIGURE 19 Flume test showing scour hole behind a pier in cohesive soil (Courtesy: Texas A&M University).

Scour History Most of the survey respondents who used fixed scour moni- toring systems reported a history of scour and/or scour critical ratings at their bridge sites. The scour observations and eval- uations were used in the decision-making process to deter- mine the number and locations of the individual monitoring instruments. Power Fifty-seven percent of the survey respondents used solar power. Thirty percent reported back-up battery power and 13% used commercial power. The respondents indicated that solar power was used at remote bridge crossings where power 24 supplies were not readily available or on long span bridges to reduce the cost of long conduit runs. Batteries were used as temporary back-ups at numerous sites. Commercial power can be used by tapping into the electrical systems at the bridge, particularly on movable bridges. Extreme Conditions and Hazardous Locations Survey respondents indicated that high velocity flows, debris, ice forces, sediment loading, and/or severe water tempera- tures were extreme conditions that were present at their bridge sites (Figure 20). However, survey results indicated that debris (41%) and ice (28%) forces caused the most damage and interference to the scour monitoring systems (Figure 21). Based on survey responses, the extent and frequency of 0 5 10 15 20 25 30 35 40 N um be r of In st al la tio ns No. 37 1 31 29 36 Debris Loading Extreme Temperatures Sediment Loading Ice Flows High Velocity Flows FIGURE 20 Extreme site conditions at scour monitoring locations. (Note: Air entrainment was surveyed, but no cases were reported.) 0 5 10 15 20 25 30 35 No. 22 32 3 4 1 8 9 Ice Flows Debris Solar PowerInterruptions Corrosion or Electrolysis Collisions Vandalism Other FIGURE 21 Site conditions that caused interference or damage to the fixed scour monitoring systems. (Note: “Other” responses included damage owing to vibration, high water velocities, and equipment being buried over time.)

25 damage was often not anticipated by the bridge owner. This resulted in much higher maintenance and repair costs than were anticipated. One respondent indicated that repair costs were double what they had budgeted. Numerous cases were also reported where new replacement instruments had to be installed after high velocity flows, debris, and/or ice forces caused the existing instrument to separate from the structure. The materials used to produce the scour monitoring instru- mentation need to be robust when there are extreme condi- tions. Many survey respondents indicated that this is an area of concern because some of the materials being used do not last long enough when severe conditions are present. Fixed monitors often need to be placed in hazardous loca- tions to monitor bridge scour. Debris or ice flows can collide with the monitors that are mounted underwater on the sub- structure and damage or destroy the devices. Debris and ice flows generally float on the top of the waterway; therefore, locating the monitors closer to the streambed can help protect the instrument from collision. Fixed monitors are generally placed in the location of the potential maximum scour. Often this is considered to be the center of the pier on the upstream side of the bridge. Depending on the angle of flow, this can also be the position where the maximum debris and ice flows collide with the bridge. Placement of the scour instrument to the side of the pier can help to protect it. As discussed in the section on soil conditions, if the streambed material is cohesive, the maximum scour hole can be to the side or back of the pier. Alaska has developed a retractable arm for mounting their sonar scour monitors. The retractable bracket is mounted under the bridge deck and the arm periodically extends out, takes the readings, and retracts under the protection of the deck. Alaska has also mounted sonar monitors in the snow (Figure 22). In Maryland, protective stainless steel shields for the sonar transducer mountings were placed on the upstream side of the approach piers on the Woodrow Wilson Memorial Bridge to protect monitors from the floating debris and boat traffic (Hunt et al. 1998). Shields were not placed on the two bascule piers being monitored because they were protected by navigation fenders of the main channel. Corrosion and marine growth in the harsh tidal environ- ments have led to the use of certain materials as well as more stringent maintenance procedures. The survey respon- dents reported the use of AISI 316 stainless steel, similar materials to avoid electrolysis, zinc anodes, and anti-fouling paint to help keep the underwater components of the mon- itoring installations operational. They noted that marine growth (Figure 23) needs to be periodically cleaned from the monitoring devices. This can be done during the underwater inspections of the bridge, but often needs to be done at shorter intervals if the bridges are on the National Bridge Inspection Standards (NBIS) five-year underwater inspection cycles (Figure 24). Access and Vandalism Selection of the various components of the scour monitoring system requires a careful balance between access and pre- vention of vandalism. Complex access requirements can FIGURE 22 Sonar monitor mounted on pier in the snow in Alaska. FIGURE 23 Underwater sonar bracket installation in the tidal environment showing the marine growth.

26 make it difficult to install, maintain, and repair a fixed scour monitoring system. Figure 25 shows a variety of locations where the master and remote stations have been placed to provide access for maintenance and to protect the stations from vandalism. Master and remote stations can be mounted on bridge abutments, piers, catwalks, sidewalks, or inside the towers on movable bridges. Master stations can also be mounted on buildings, bulkheads, or other structures in the vicinity of the bridge. Additional parties or equipment can be required, such as divers, boats, and barges, both to install, and later to access the system for maintenance and repairs. These items must be given serious consideration especially when planning a maintenance and repair program and budget. Examples of access limitations include security clearances, traffic lane closures, boats, barges, keys to doors or gates, and under bridge inspection trucks (Figures 26 and 27). Survey FIGURE 24 Underwater sonar bracket installation in the tidal environment showing corrosion. FIGURE 25 Locating the master and remote stations (clockwise from left to right). Master stations mounted inside a bascule pier machinery room and on a building near the bridge, remote stations on a pier stem, a catwalk under the bridge, and on a pier pile cap.

27 responses showed that 47% of the scour monitoring systems required access by boat. The high costs of owning or renting a boat and the increased personnel needed to operate the boat have made maintenance of some monitoring installations difficult or, without funding, some have been abandoned. Additionally, there are waterways in the northern states that cannot be navigable during the winter, so that maintenance and repairs to the systems can only be done during certain months of the year. Access is important, but if a scour monitoring system is too readily accessible, vandalism can occur. Ten percent of the respondents indicated that damage to their scour monitoring systems was the result of vandalism. These unexpected repairs increased the cost of maintaining the system. One survey respondent reported that monitoring was discontinued because of repeated vandalism. Environmental Concerns The installation of fixed instrumentation on a bridge can require permitting. Consideration needs to be given to envi- ronmental concerns. Installation of fixed instrumentation such as magnetic sliding collars and float-out devices require drilling. In addition, the magnetic sliding collars and float-out devices have mercury switches that need to be contained to protect the fish habitat. RAILROAD BRIDGES Inquiries were made with Association of American Railroads, FRA, and Burlington Northern and Santa Fe regarding the use of fixed scour monitoring systems on railroad bridges in the United States; however, none were identified from these inquiries and the literature search. Several of the rail- road owners described their procedures regarding monitor- ing and scour critical bridges. Their monitoring is most frequently visual (inspection) monitoring. Many railroads have procedures that require trains to be operated at restricted speeds when approaching, and running over, scour critical bridges during periods of heavy rain. As used in railroad operating rules, “restricted speed” means a speed of less than 20 mph that allows stopping within half the range of vision, short of listed hazards, while watching for a broken rail. Railroad dispatchers can communicate with trains by means of radio to control their movements. They can instruct their trains to reduce their speeds or stop and inspect a bridge. The fixed instrumentation commonly used on many rail- road lines is a simple device called a high water detector. Although these devices do not monitor scour, they can cer- tainly indicate the presence of conditions that could cause scour. The high water detector will sense a threshold water elevation at its location near, and upstream from, the track and bridge. At a particular bridge, if the water level gets high enough, an alert can be sent to trains, the train dispatcher, and/or maintenance personnel, who can then take appropriate action. Timely inspections can then be initiated. This warning device can activate a stop signal when the water surface elevation has reached a level that can damage the track or bridge. It is likely that high water detectors are most com- monly used in the western United States where dry washes FIGURE 26 Installation of solar panels, remote stations, and conduit requires a snooper truck. FIGURE 27 Installation of an underwater sonar bracket requires divers and a boat.

can turn into rapidly flowing rivers for a few hours or days after a rainstorm. Additionally, the railroads often have inspection programs during and after major storms. These programs typically involve inspection from an on-track vehi- cle running ahead of trains. In Japan, the East Japan Railway Company has used clinometers to monitor scour at their bridges (Suzuki et al. 2007). They report that they cancel trains based on observa- tions of the inclination of bridge piers owing to scour. They have placed clinometers as scour monitoring devices on top of the bridge pier to monitor the inclination angle in real time. The threshold angle for train suspension is derived from a geometric relationship between the inclination angle of the bridge pier and the maintenance limits of track irregularity. 28 When an inclination angle of a bridge pier exceeds the threshold angle, the device triggers an alarm to suspend train operation. Suzuki reports that the problem with using this type of device is that it cannot issue an alarm before a bridge pier is inclined. He points out that even if the inclination angle of a bridge pier is minute, reconstruction of the pier tends to take a long time, is expensive, and includes suspension of train service. They reported a case in 1995 of an inclined bridge pier that resulted in the suspension of train operation for four days for emergency reconstruction, and more than one year to reconstruct the inclined pier. They are currently working on a project to develop a new technology to alert if there is scour damage before the inclination of a pier. Infor- mation on this project can be found in chapter seven in the section on current studies on instrumentation.