Water surface slope extending up to 20 channel widths up and downstream of crossing.

Transcription

1 Site Evaluations Site Information Site Location: Mt ood NF, Forest Road 7 Year Installed: Pre-987 Lat/Long: 8 W Watershed rea (mi ): N Stream Slope (ft/ft) : Channel Type: Step-pool ankfull Width (ft): Survey Date: pril, 7 Water surface slope extending up to channel widths up and downstream of crossing Culvert Information Culvert Type: Open-bottom arch Culvert Material: nnular CMP Culvert Width: 9 ft Outlet Type: ybrid projecting/mitered Culvert Length: 7 ft Inlet Type: ybrid projecting/mitered Pipe Slope (structure slope): Culvert ed Slope: (First hydraulic control upstream of inlet to first hydraulic control downstream of outlet) Culvert width as a percentage of bankfull width: 8 lignment Conditions: ppears inline with natural channel ed Conditions: Scoured at upstream end of pipe Large cobbles to large boulders are creating steps in culvert Pipe Condition: Left footing severely undermined at upstream end May be some piping around sides of pipe where erosion has occurred ydrology Discharge (cfs) for indicated recurrence interval % -yr Q bf -year -year -year -year -year ankfull flow estimated by matching modeled water surface elevations to field-identified bankfull elevations 7

2 Culvert Scour ssessment Points represent survey points Figure Plan view map 8

3 Site Evaluations istory The exact installation date is unknown, but the culvert was included in the 987 Western Federal Lands ighway Division (WFLD) Oregon Culvert Fish Passage Survey The field survey for the WFLD study was conducted on November 7, 987 The study describes the culvert as an open bottom arch with boulders placed inside the barrel With respect to fish passage, Oregon Department of Fish and Wildlife (ODFW) staff described the culvert as an excellent open bottom arch installation; whereas WFLD staff noted that the culvert was in fair condition, the foundation was in poor condition, and there was moderate outlet scour The culvert hydraulics were considered compatible with the natural stream hydraulics They go on to note that open-bottom arches with shallow foundations are susceptible to scour and recommend that if foundation requirements cannot be met (ie, embedment depth), then closed-bottom pipes should be installed The following are photos from the WFLD study: Culvert inlet Typical stream channel Site Description The culvert is an open-bottom arch that projects from the roadfill The culvert is characterized by a deep scour pool at the inlet, primarily concentrated along the left side of the culvert where significant footing scour and undermining has occurred Downstream of the scour pool, the bed is aggraded and levels off forming a consistent riffle The channel is against the left side of the culvert for most of its length There has been deposition of material along the right footing at the inlet There is a large (greater than -foot diameter) log just upstream and inside of the culvert There is significant erosion at the sides of the culvert at the inlet and outlet The upstream representative reach consists of a moderate gradient step-pool channel The upstream segment sits in a fairly confined and narrow valley Channel banks are steep with high adjacent terraces that may only be active at infrequent floods Large boulders and fallen trees line both banks The reach consists of a series of steps and pools The downstream representative reach consists of a series of steep riffles interspersed with pools relatively extensive low (active) flood plain exists through this reach ed material was finer and there were small log jams 9

4 Culvert Scour ssessment Survey Summary Fourteen cross sections and a longitudinal profile were surveyed at the crossing in pril 7 to characterize the culvert, an upstream representative reach, and a downstream representative reach Representative cross sections in the culvert were taken through the downstream end of the pool and the riffle One additional cross section was surveyed upstream to characterize the inlet as well as the contraction of flow nother two cross sections were surveyed downstream of the culvert to characterize the outlet and the expansion of flow Four cross sections were surveyed to characterize the upstream representative reach; one at the upstream boundary, one at the downstream boundary, one through a step, and one through a pool Four cross sections were also surveyed to characterize the downstream representative reach; one at the upstream boundary, one at the downstream boundary, one through a pool, and one through a riffle Profile nalysis Segment Summary The profile analysis resulted in a total of eight profile segments The two consecutive segments downstream of the outlet, though similar in gradient, were not combined in order to separate out the transition area from the downstream representative channel The culvert consisted of two profile segments, the upstream one extending into the upstream transition area The upstream culvert segment was compared to two representative profile segments, one in the upstream channel and one in the downstream channel There was no suitable comparison for the downstream segment in the culvert The upstream transition segment was compared to a representative profile segment in the downstream channel The downstream transition segment was compared to two representative profile segments, one in the upstream channel and one in the downstream channel See figure and table Scour Conditions Observed conditions Footing scour The greatest amount of footing scour is at the upstream end on the left bank where the footing is undermined The base of the footing is suspended above the bed feet at the maximum depth of the scour pool The lateral extent of scour under the footing reaches feet at one location Some of this scour may be the result of a large log (greater than -foot diameter) located at the inlet pproximately percent of the footing on the left bank is undermined and all of it is exposed There is also scour around the sides of the pipe at the inlet and outlet and there may be some piping of flow around the culvert in these areas The poor foundation rating from the WFLD study and the suggestion regarding foundation requirements suggest that some foundation undermining may have been present in 987, but likely less than in 7 or there would have been more mention of it Culvert-bed adjustment The culvert bed has reduced its slope since installation (assuming the culvert bed was constructed at the same gradient as the structure) This flattening appears to be mostly due to scour in the upstream portion of the pipe There is still streambed material throughout the pipe and no bedrock is present on the bed Profile characteristics The profile has a concave shape through the crossing (figure ) This shape reflects scour at the inlet region There is a natural valley transition in this area Upstream is more confined with higher and less active floodplain terraces than the downstream reach Residual depths The single culvert residual depth is within the range of residual depths in corresponding profile segments in the natural channel ( and ) (figure ) The single residual depth in the downstream transition is also within the range of corresponding profile segments in the natural channel ( and ) There was no residual depth in the corresponding profile segment for the upstream transition

5 Site Evaluations Substrate ed-material distributions are similar between the culvert and channel sample sites The culvert has more coarse material than the downstream channel but similar abundance of coarse material as the upstream channel The downstream channel has the greatest abundance of fine material Sorting and skewness values in the culvert are within the range of those in the natural channel (table 7) Predicted conditions *Note: s estimated in the model, backwater from the culvert affects portions of the upstream reach (figure ) The backwater affects the upstream representative reach for the Q and Q For this reason, hydraulic metrics for these flows are not used in the comparisons with culvert values Cross-section characteristics The culvert appears to affect most of the cross-section metrics at the Q bf and above (figures through 9 and through 9) There is a dramatic reduction in top width and an increase in depth as flows rise The culvert exhibits characteristics of outlet control, with culvert characteristics (ie, barrel roughness, slope, and area) creating deep subcritical flow throughout most of the barrel length The flow passes through critical depth near the downstream end Cross-section characteristics at the upstream transition (F) are impacted by the culvert backwater at higher flows (Q and Q ) t lower flows, the flow has lower width and greater depth than the corresponding profile segments (), but this may be due partially to changes in valley confinement Cross-section characteristics in the downstream transition (C) are mostly within the range of corresponding profile segments ( and ) Shear stress The modeling suggests that shear stress is low in the culvert due to backwater conditions that reduce the energy grade Shear stress near the downstream end of the culvert is high where the flow passes through critical depth (figure ) Shear stress in the upstream transition (F) is greater than the corresponding profile segment () for flows up to the Q but is less at the Q and Q because of backwater effects (figures and 9) Shear stress in the downstream transition (C) is within the range of corresponding profile segments ( and ) Excess shear The excess shear analysis shows the culvert as having lower potential for bed mobilization when compared to the upstream and downstream channels (figure ) This is due to the backwater effect of the culvert that lowers the energy grade and therefore lowers the applied shear available to move material Velocity The modeling suggests that velocity is low in the culvert due to backwater conditions that reduce the energy grade Velocity near the downstream end of the culvert is high where the flow passes through critical depth (figure ) Velocity in the upstream transition (F) is similar to the corresponding channel segment () at the Q and below but is lower than the channel at the Q and Q (figure 8) due to backwater effects Velocity in the downstream transition (C) is within the range of corresponding channel segments ( and ) at all modeled flows Scour summary There is severe scour of the left bank footing at the inlet and extending downstream approximately feet This is a serious maintenance issue that needs to be addressed to ensure that the structural integrity of the crossing is not compromised This scour may be partially related to culvert capacity, deposition of coarse material upstream of the inlet, and a large (greater than -foot diameter) midchannel log just upstream and inside of the culvert The drop into the scour pool is larger than any drops observed in the reference reaches This has also resulted in the deposition of material along the right footing at the inlet and the shifting of the channel towards the left Downstream of the scour pool, the bed is aggraded and levels off forming a consistent riffle

6 Culvert Scour ssessment ed material at the inlet has likely eroded out and redeposited at the downstream portion of the culvert, contributing to bed flattening Modeling suggests that flow geometry and hydraulics are highly impacted by the culvert, especially at high flows that cause backwater within and upstream of the culvert The culvert appears to be under outlet control at high flows, with the length, roughness, and downstream conditions raising the elevation of the flow through much of the culvert This condition serves to reduce channel velocity and shear stress through most of the culvert at very high flows (Q and above) t these flows, the modeling shows flow passing through critical depth near the downstream end of the culvert, with associated high shear stress and velocity that could cause scour at this location Prior to the inlet scour, which widened the inlet area, the culvert may have exhibited inlet control conditions that contributed to the scour observed in the inlet area t more frequent flood events, inlet control conditions may still be a concern, especially with respect to the potential for increased scour of the footing at the inlet There is also significant erosion at the sides of the culvert at the inlet and outlet, possibly a result of flow contraction and expansion Erosion at the left bank upstream of the inlet is further exacerbated by the coarse material and logs that have deposited upstream of the inlet, thus initiating lateral boundary adjustment OP Conditions Cross-section complexity The sum of squared height differences in the culvert cross sections are both within the range of those in the channel cross sections (table ) Profile complexity Vertical sinuosity in the upstream culvert segment (E) is slightly greater than the values in the corresponding channel segments ( and ) (table ) Vertical sinuosity in the upstream transition segment (F) is slightly greater than the value in the corresponding channel segment () Vertical sinuosity in the downstream transition segment (C) is within the range of values in the corresponding channel segments ( and ) Depth distribution The upstream culvert cross section has less channel margin habitat than the natural channel but the downstream culvert cross section is within the range of the natural channel (table ) abitat units abitat-unit distribution in the culvert is within the range of that found in the natural channel upstream and downstream of the crossing (table ) Residual depths The single culvert residual depth is within the range of residual depths in corresponding profile segments in the natural channel ( and ) (figure ) The single residual depth in the downstream transition is also within the range of corresponding profile segments in the natural channel ( and ) There was no residual depth in the corresponding profile segment for the upstream transition Substrate ed-material distributions are similar between the culvert and channel sample sites The culvert has more coarse material than the downstream channel but similar abundance of coarse material as the upstream channel The downstream channel has the greatest abundance of fine material Sorting and skewness values in the culvert are within the range of those in the natural channel (table 7)

7 Site Evaluations Large woody debris There was one - to -footdiameter piece of LWD present at the inlet to the culvert The piece may have been a contributor to the scour present at the inlet The representative channel had high LWD abundance (table 8) LWD formed steps and scour pools in the channel outside the crossing and played a primary role in habitat-unit creation and complexity Features in the culvert did not mimic the role of wood in the natural channel OP summary Complexity measures and site observations suggest that this is a good installation with respect to OP There is good flow concentration in the culvert that would support fish passage at low flows The hydraulics at the Q bf and below are unaffected by the backwater effects described earlier and are assumed to be amenable to fish passage There is also a dry bank along the right side suitable for passage of terrestrial organisms There is also erosion on the sides of the culvert at the inlet and outlet These areas should be stabilized with rock or concrete (eg, wing-walls) to prevent erosion around the edges of the pipe Regular maintenance of the site is needed to remove woody debris, such as the large log that is located at the inlet and may be contributing to the inlet scour ased on the presence of log jams in the natural channel, wood transport is common through this portion of Maintenance needs to be conducted to manage for this wood or the crossing needs to be made wide enough to convey wood Design Considerations This site is a poor installation with respect to scour but appears to be suitable for OP There are serious concerns with the structural integrity of the structure that are primarily related to the undermining of the left-bank footing at the upstream end of the culvert dditionally, modeling suggests a severe effect on flow geometry and hydraulics at the Q and above that may create future scour problems within the pipe This design could be improved by use of a wider culvert with greater capacity to convey high flood flows It is also clear that the footing depth needs to be increased to extend below the depth of maximum potential scour

8 Culvert Scour ssessment 9 Relative 9 elevation (feet) 8 S e g m e n t XS S e g m e n t L e n g th ( f t) S e g m e n t G r a d ie n t C D 7 E 7 F G XS : Pebble count (riffle) XS : Pebble count (pool) XS C XS XS D C ulvert XS 7: Pebble count (riffle) E XS 8: Pebble count (pool) Large log in inlet XS 9 XS Representative Channel 8 Dis tance along bed (feet) Figure longitudinal profile Table Segment comparisons R epres en ta tiv e C h a n n el S egmen t % D ifferen c e in G ra dien t C u lv ert S egmen t E 7% E 9% U ps tream T rans ition F 97% D o w n s trea m T ra n s itio n C % C % F XS G XS XS : Pebble count (step) XS : Pebble count (pool) Representative Channel

9 Site Evaluations Table Summary of segments used for comparisons Segment Range of Manning's n values # of measured XSs # of interpolated XSs C 7 E F Obtained using equation from Jarrett (98): n = 9S8R-, where S=stream slope; R=hydraulic radius Jarrett s equation only applied within the following ranges: S = to 8, R = ft to 7 ft For cross-sections outside these ranges, n was computed either from adjacent sections that fell within the ranges, using the guidance of rcement and Schneider (987), or from the EC-RS recommendations for culvert modeling L e ge nd Culvert W S Q W S Q W S Q W S Qbf W S c fs Ground Elevation (ft) * * * * * 7 * * 7 7 * 7 * * Main Channel Dis tance (ft) Stations with decimal values are interpolated cross sections placed along the surveyed profile Figure EC-RS profile

10 Culvert Scour ssessment RS = RS = L e ge nd L e ge nd WS Q 8 WS Q WS Q WS Q 8 WS Q WS Q WS Qbf WS Qbf WS cfs WS cfs Ground 8 Ground ank St a ank St a l 8 i Station (ft) Station (ft) RS = RS = L e ge nd 8 WS Q WS Q WS Q 8 E WS Qbf l t a v e i Elevation (ft) Elevation (ft) ) t f ( n o L e ge nd WS Q WS Q WS Q WS Qbf WS c fs WS cfs 8 Elevation (ft) Elevation (ft) Ground Ground ank St a ank St a 8-8 Station (ft) Station (ft) Figure Cross-section plots Only measured cross sections are included Manning s n values are included at the top of the cross section The stationing (RS) corresponds to the stationing on the EC-RS profile Green arrows define the ineffective flow areas lack arrows represent points surveyed in as the bankfull channel boundary Only those points called out in the field and supported by further hydraulic and topographic analyses are marked below ) t f ( n o t a v e E

11 Site Evaluations RS = 9 RS = L e ge nd WS Q 8 WS Q 8 WS Q E WS Qbf WS cfs Elevation (ft) Ground 98 ank St a Station (ft) Station (ft) RS = 7 RS = 8 L e ge nd L e ge nd WS Q 9 WS Q 8 WS Q 8 WS Q WS Q l t a v e WS Q i ) t f ( n o L e g e n d W S Q W S Q W S Q W S Qb f WS cfs G rou nd Elevation (ft) Le ve e Ine ff an k S ta WS Qbf WS Qbf WS c fs WS cfs Elevation (ft) Elevation (ft) Ground Ground 98 ank St a 98 ank St a Station (ft) Station (ft) Figure Cross-section plots Only measured cross sections are included Manning s n values are included at the top of the cross section The stationing (RS) corresponds to the stationing on the EC-RS profile Green arrows define the ineffective flow areas lack arrows represent points surveyed in as the bankfull channel boundary Only those points called out in the field and supported by further hydraulic and topographic analyses are marked below (continued) 7

12 i l i l Culvert Scour ssessment RS = Station (ft) ) t f ( n o t a v e L e g e n d W S Q W S Q W S Q W S Qb f WS cfs G rou nd Ine ff an k S ta Elevation (ft) E L e g e n d W S Q W S Q W S Q W S Qb f RS = Station (ft) Elevation (ft) WS cfs G rou nd Ine ff an k S ta L e ge nd WS Q WS Q WS Q WS Qbf WS c fs Ground ank St a RS = Station (ft) Elevation (ft) L e ge nd WS Q WS Q WS Q WS Qbf WS c fs Ground ank St a RS = Station (ft) Elevation (ft) Figure Cross-section plots Only measured cross sections are included Manning s n values are included at the top of the cross section The stationing (RS) corresponds to the stationing on the EC-RS profile Green arrows define the ineffective flow areas lack arrows represent points surveyed in as the bankfull channel boundary Only those points called out in the field and supported by further hydraulic and topographic analyses are marked below (continued) 8 ) t f ( n o t a v e E

13 Site Evaluations RS = RS = L e ge nd WS Q WS Q WS Q WS Qbf WS c fs Ground ank St a Station (ft) Elevation (ft) L e g e n d W S Q W S Q W S Q W S Qb f WS cfs G rou nd Le ve e an k S ta Station (ft) Elevation (ft) Figure Cross-section plots Only measured cross sections are included Manning s n values are included at the top of the cross section The stationing (RS) corresponds to the stationing on the EC-RS profile Green arrows define the ineffective flow areas lack arrows represent points surveyed in as the bankfull channel boundary Only those points called out in the field and supported by further hydraulic and topographic analyses are marked below (continued) Main Channel Distance (ft) Figure Flow area (total) profile plot 9 ) t f q s ( a e r Legend Flow rea Q w o F l Flow C D E F G Culvert Flow rea Q Flow rea Q Flow rea Qbf Flow rea cfs Flow area (sq ft)

14 Culvert Scour ssessment Legend WP Total Q WP Total Q Flow C D E F G Culvert 8 Main Channel Distance (ft) Figure Wetted perimeter Flow 8 Main Channel Distance (ft) Figure 7 ydraulic radius WP Total Q WP Total Qbf WP Total cfs ) t f ( s u d a R r d y Legend ydr Radius Q C D E F G Culvert ydr Radius Q ydr Radius Q ydr Radius Qbf ydr Radius cfs i WP total (ft) ydraulic radius (ft)

15 Site Evaluations Legend Top Width Q Top Width Q Flow C D E F G Culvert 8 Top Width Q Top Width Qbf Top Width cfs Main Channel Distance (ft) Figure 8 Top width 8 Main Channel Distance (ft) Figure 9 Maximum depth ) t f ( h t p D h C x a M l Legend Max Chl Dpth Q Max Chl Dpth Q Max Chl Dpth Q Max Chl Dpth Qbf Max Chl Dpth cfs Top width (ft) Flow C D E F G Culvert Maximum channel depth (ft)

16 Culvert Scour ssessment Legend Shear Chan Q Shear Chan Q Shear Chan Q Shear Chan Qbf Shear Chan cfs Flow C D E F G Culvert l l Shear channel (lbs/sq ft) Main Channel Distance (ft) *Note: Shear at station for the Q and Q are greater than pounds per square foot and are therefore not shown Figure Shear stress (channel) profile Legend Vel Chnl Q Flow Main Channel Distance (ft) Figure Velocity (channel) profile plot s ) / t f ( C D E F G Culvert Vel Chnl Q Vel Chnl Q Vel Chnl Qbf Vel Chnl cfs Velocity channel (ft/sec) n h C e V

17 Site Evaluations ox Plot Explanation Maximum value 7th percentile Median (aka th percentile) % of the values % of the values th percentile Minimum value Flow rea (ft) Flow area (ft ) %Q Qbf Figure Flow area (total)

18 Culvert Scour ssessment 9 Wetted Perimeter (ft) Wetted perimeter (ft) %Q Qbf Figure Wetted perimeter ydraulic Radius (ft) ydraulic radius (ft) %Q Qbf Figure ydraulic radius

19 Site Evaluations 8 Top width (ft) Top Width (ft) %Q Qbf Figure Top width 8-8 Maximum Depth (ft) Maximum depth (ft) %Q Qbf Figure Maximum depth

20 Culvert Scour ssessment 8 Width-to-depth Ratio Width-to-depth ratio %Q Qbf Figure 7 Width-to-depth ratio 8 Velocity (ft/sec) Velocity (ft/sec) %Q Qbf Figure 8 Velocity (channel)

21 Site Evaluations Shear Stress (lbs/ft) Shear stress (lbs/ft ) %Q Qbf Figure 9 Shear stress (channel) US Channel (DS pebble count) - step Culvert (DS pebble count) - riffle DS Channel (DS pebble count) - riffle Excess Shear (pplied / tcrit) Discharge (cfs) Excess shear (pplied/tcrit) Excess shear stress is the channel shear divided by the critical shear for bed entrainment of the D 8 particle size Values of excess shear greater than indicate bed movement for the D 8 particle size Figure Excess shear stress 7

22 Culvert Scour ssessment Table Sum of squared height difference Reach XS Unit Sum of squared Within range of Location type height difference channel conditions? Culvert US Pool Yes DS Riffle Yes Upstream US Pool DS Step Downstream US Pool DS Riffle Table Vertical sinuosity Segment Location Vertical Sinuosity (ft/ft) DS channel DS channel 9 C DS transition 7 D Culvert E Culvert F US transition G US channel US channel 7 Table Depth distribution Reach XS % Q Within range of Location channel conditions? Culvert US No Upstream US DS Yes DS Downstream US DS 8 8

23 Table abitat unit composition Percent of surface area Reach Pool Glide Riffle Step Culvert % % % % Upstream Channel 8% % % % Downstream Channel % % 7% % Site Evaluations Residual Depth (ft) 8 Segment Segment Segment C DS Transition Segment D Culvert Segment E Culvert Segment F US Transition Segment G Segment Figure Residual depths Table 7 ed material sorting and skewness Reach XS Unit Sorting Within range Skewness Within range Location Type of channel of channel conditions? conditions? Culvert US Pool Yes Yes DS Riffle 7 Yes Yes Upstream US Pool 9 DS Step Downstream US Pool DS Riffle 7 9

24 Culvert Scour ssessment Table 8 Large woody debris Reach Pieces/Channel Width Culvert ` Upstream Downstream Terminology: US = Upstream DS = Downstream RR = Reference reach XS = Cross section

25 Site Evaluations View upstream through culvert View downstream through culvert View downstream of culvert inlet View of undercut left bank footing at upstream end of culvert Downstream reference reach Upstream reference reach

26 Culvert Scour ssessment Cross Section: Upstream Reference Reach Upstream Pebble Count Material S ize C las s (mm) C ount Item % C umulative % sand < % % very fine gravel - % % fine gravel - 7 % % fine gravel 7-8 % % medium gravel 8 - % % medium gravel - % 8% coarse gravel - % 9% coarse gravel - % % very coarse gravel - 8 9% % very coarse gravel - 9 % % small cobble % 9% medium cobble 9-8 % % large cobble % 9% very large cobble 8 - % 7% small boulder - % 8% small boulder - 9 % 9% medium boulder - % % large boulder - 8 % % very large boulder 8-9 % % bedrock edrock % % Frequency 8 < Particle Size Category (mm) edrock % 9% 8% 7% % % % % % % % Cumulative Frequency S ize C las s S ize perc ent finer than (mm) D D D D8 9 D9 D 9 Material P ercent C ompos ition Sand % Gravel % Cobble % oulder 9% edrock % Sorting Coefficient: 9 Skewness Coefficient:

27 Site Evaluations Cross Section: Upstream Reference Reach Downstream Pebble Count Material S ize C las s (mm) C ount Item % C umulative % sand < % % very fine gravel - % % fine gravel - 7 % % fine gravel 7-8 % % medium gravel 8 - % % medium gravel - % % coarse gravel - % % coarse gravel - % % very coarse gravel - % % very coarse gravel - % % small cobble % % medium cobble 9-8 7% 9% large cobble 8-8 % % very large cobble 8 - % 9% small boulder - % 7% small boulder - % 87% medium boulder - % % large boulder - 8 % % very large boulder 8-9 % % bedrock edrock % % Frequency 8 % 8% % % % % Cumulative Frequency < Particle Size Category (mm) edrock -% S ize C las s S ize perc ent finer than (mm) D D 78 D D8 D9 D 7 Material P ercent C ompos ition Sand % Gravel % Cobble 7% oulder % edrock % Sorting Coefficient: Skewness Coefficient:

28 Culvert Scour ssessment Cross Section: Culvert Upstream Pebble Count Material S ize C las s (mm) C ount Item % C umulative % sand < % % very fine gravel - % % fine gravel - 7 % % fine gravel 7-8 % % medium gravel 8 - % % medium gravel - % 8% coarse gravel - % % coarse gravel - % % very coarse gravel - 7 7% % very coarse gravel - 7 7% % small cobble % 9% medium cobble % 9% large cobble % 7% very large cobble 8-9 9% 8% small boulder - % 89% small boulder - 9 9% 98% medium boulder - % % large boulder - 8 % % very large boulder 8-9 % % bedrock edrock % % Frequency 8 8 < Particle Size Category (mm) edrock % 9% 8% 7% % % % % % % % Cumulative Frequency S ize C las s S ize perc ent finer than (mm) D D D D8 D9 7 D Material P ercent C ompos ition Sand % Gravel 9% Cobble % oulder % edrock % Sorting Coefficient: Skewness Coefficient:

29 Site Evaluations Cross Section: Culvert Downstream Pebble Count Material S ize C las s (mm) C ount Item % C umulative % sand < % % very fine gravel - % % fine gravel - 7 % % fine gravel 7-8 % % medium gravel 8 - % % medium gravel - % % coarse gravel - % 9% coarse gravel - % % very coarse gravel - % % very coarse gravel - 7 7% % small cobble % % medium cobble 9-8 % % large cobble 8-8 7% % very large cobble 8 - % % small boulder - % 8% small boulder - % 9% medium boulder - % % large boulder - 8 % % very large boulder 8-9 % % bedrock edrock % % Frequency 8 8 % 9% 8% 7% % % % % % % % Cumulative Frequency < Particle Size Category (mm) edrock S ize C las s S ize perc ent finer than (mm) D 8 D 9 D D8 8 D9 D 9 Material P ercent C ompos ition Sand % Gravel % Cobble % oulder % edrock % Sorting Coefficient: 7 Skewness Coefficient:

30 Culvert Scour ssessment Cross Section: Downstream Reference Reach Upstream Pebble Count Material S ize R ange (mm) C ount Item % C umulative % sand < % % very fine gravel - % % fine gravel - 7 % % fine gravel 7-8 % % medium gravel 8 - % % medium gravel - % % coarse gravel - % % coarse gravel - % % very coarse gravel - % 8% very coarse gravel - % 8% small cobble % % medium cobble 9-8 % % large cobble % 8% very large cobble 8 - % 9% small boulder - % 97% small boulder - % % medium boulder - % % large boulder - 8 % % very large boulder 8-9 % % bedrock > 9 % % % 8 9% Frequency 8 8% 7% % % % % Cumulative Frequency % % % < Particle Size Category (mm) edrock S ize C las s S ize perc ent finer than (mm) D D D D8 D9 D Material P ercent C ompos ition Sand % Gravel 8% Cobble % oulder 9% edrock % Sorting Coefficient: Skewness Coefficient:

31 Cross Section: Downstream Reference Reach Downstream Pebble Count Material S ize C las s (mm) C ount Item % C umulative % sand < 8 8% 8% very fine gravel - % 9% fine gravel - 7 % 9% fine gravel 7-8 % % medium gravel 8 - % % medium gravel - % % coarse gravel - 8 8% % coarse gravel - 9 9% % very coarse gravel - % % very coarse gravel - 9 9% % small cobble - 9 % 8% medium cobble 9-8 % % large cobble % 7% very large cobble 8-8 8% 78% small boulder - % 9% small boulder - 7 7% 97% medium boulder - % % large boulder - 8 % % very large boulder 8-9 % % bedrock edrock % % Site Evaluations Frequency 8 % 9% 8% 7% % % % % % % % Cumulative Frequency < Particle Size Category (mm) edrock S ize C las s S ize perc ent finer than (mm) D D 8 D D8 D9 D 7 Material P ercent C ompos ition Sand 8% Gravel 7% Cobble % oulder % edrock % Sorting Coefficient: Skewness Coefficient: 7 7