TIDEROUT2 - GISHydro
Contents
1. Bridge Opening Data Roadway Data Output Graphic Constant Flow Discharge cfsicms ag Stream Flow Option C Given Hydrograph Stream Flow Hydrograph Discharge cfsicms A Insert row Generate Hydrograph STREAM FLOW OPTION The User has two options with regard to stream flow data The objective is to get a conservative yet reasonable model combining tidal flow and riverine stream flow that includes the peak tidal flow and the peak riverine flow e Given Hydrograph A conservative approach would be to arrange the time of a riverine hydrograph to peak at the same time as the tidal hydrograph peaks usually time zero Judgment is needed to decide whether it is reasonable to assume that the time of concentration of the riverine hydrograph will coincide with the peak tidal hydrograph e Constant Discharge A second option is to convert the riverine hydrograph to a hydrograph with a constant discharge The height discharge of this rectangular hydrograph is determined by dividing the total area runoff volume under the hydrograph by the length of the hydrograph base This approach has the advantage of combining tidal and riverine flows when the relative timing of peak flows is problematical CONSTANT FLOW DISCHARGE If the constant discharge option is selected input the value of the computed constant flow discharge otherwise leave this field blank STREAM FLOW HYDROGRAPH If the stream flow hydrogra2. Area sfism HS Bei A A Insert row 2 528 Delete row Bridge Road Tool MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 12 Discharge Coefficient Refer to F 1 Help For 1 bridges the default value has been selected as 0 80 For larger bridges particularly those with streamlined abutments a higher value may be appropriate Bridge Waterway Area Opening Rating Table The waterway area rating table is provided by the user as a set of elevation vs waterway area pairs See F 1 Help The waterway area for various water surface elevations can be measured from the bridge plans ROADWAY DATA TIDEROUT2 C 12008 old stuff on tidal hydraulics 2008 fred tidal presentation EXAMPLE 1 4_11_08 tid File Run Draw Tools Help Project Data Stream Flow data Tidal Basin Data l Bridge Opening Data Roadway Data Output Graphic Weir Flow Coefficient Cw 2 5 Use default value Roadway Profile Ascending Station Order Station fim Elevation fim 1 100 Insert Row 4 46 _Insert Row 4 09 Delete Row 3 2 3 61 Bridge Road Tool 42 2 5 3 23 2 8 2 62 2 35 2 95 3 2 43 MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 13 Weir Flow Coefficient See F 1 Help Roadway Profile Ascending Station Order See F 1 Help Boundary Conditions This roadway data card represents a very important boundary condition for evaluating tidal flow through the bridge For many Eastern
3. Shore bridges roadway elevations will be below storm tide elevations and a large quantity of the tidal prism will flow over the road instead of through the bridge Similarly if the watershed boundaries for the tidal basin are lower than the peak storm tide elevations it may not be possible to estimate the peak tidal flows through the bridge For this condition the recommended approach is to input an extended roadway length at the watershed overtopping elevation This will serve to define the flows through the bridge as those flows below the elevation of the watershed divide Program Output The output consists of two parts 1 a summary of the information input to the program by the user and 2 a time sequence of the changing hydraulic characteristic of the flow during passage of the selected tide and riverine hydrographs OUTPUT PRINTOUT PART 1 SUMMARY OF USER INPUT MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 14 Bridge Opening Data Discharge Coefficient 6 Bridge Opening Area rating Table Dataf Elevation ft Area sf L 6 8 0 Fa 3 228 3 2 528 4 3 588 5 10 588 Roadway Data Weir Flow Coefficient For Overtopping Flow 2 5 Roadway Profile Dataf Station ft Elevation ft l 100 4 2 720 4 46 3 1640 4 09 4 2340 5 5 2780 3 2 6 3060 3 61 3789 4 2 8 4730 2 5 3 5000 3 23 10 6000 2 8 11 6500 2 62 12 7500 2 35 13 38200 2 95 14 9400 3 2 15 3700 4 3 MD SHA OFFICE OF STRUCTURES TIDER
4. depth is computed as 7 6 feet Surface and subsurface boring samples indicate that the channel bed is comprised of a medium sand with a D50 of 0 0016 feet Clear Water Scour Equation Va amp Ya from TIDEOUT output q Yo Yo Yo Ye from chart Contraction Scour Flow Depth 4 W i Contraction scour Depth Y Y Yo The values of vo 6 9 fps and yo 7 6 feet are known values obtained from the TIDEROUT output tables and the value of y is the total scour depth we wish to calculate This missing variable is Vc the critical velocity of the sand which can be obtained from the chart below excerpted from the ABSCOUR 9 Users Manual For a flow depth of 7 6 feet and a particle size of 0 0016 the critical velocity of the sand 1s estimated as 3 6 fps MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 20 Solve the equation for y2 total contraction flow depth including flow depth e q Vo yo Ve y2 then e y2 q Ve Vo Ve yo 6 9 3 7 7 6 14 2 ft Contraction scour depth ys y2 yo 14 2 7 6 6 6 say 7 feet Total Abutment Scour Depth y2a y2a 1 4 y2 1 4 14 2 19 9 ft 6 Abutment scour ysa ysa y2a yo 19 9 7 6 12 feet The estimates of 7 feet of contraction scour and 12 feet of abutment scour should be evaluated in the context of the Office of Structures policies in Chapter 11 to determine the appropriate design for the bridge abutments If the bridge foundations
5. now 1 1 _insertrow_ 1 l if l r Delite rw a 10600000 Dreta row 1 l 1 l U U 1 1 1 l U l I 1 U l 1 i 1 lo 0 551000 d 158000000 10 16000000 MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 11 The user creates a storage area rating table for the tidal basin upstream of the bridge using the Tidal Basin card Beginning with the elevation of the channel bottom at the bridge usually a negative value below zero the information is provided as a set of elevation area pairs The areas corresponding to the elevations can be obtained by measuring the areas between successive contour lines See F 1 help The upper limit of the rating table should be selected as an elevation above the design storm tide elevation The area contained within a given contour line can be measured with a planimeter or can be computed using appropriate software i e GIS Systems CADD Programs topographic digital elevation models etc BRIDGE WATERWAY OPENING DATA TIDEROUT 2 C 2008 old stuff on tidal hydraulics12008 fred tidal presentation EXAMPLE 1 4_11_08 tid File Run Draw Tools Help Project Data Stream Flow data Tidal Basin Data Bridge Opening Data Roadway Data Output Graphic Discharge Coefficient Cd 6 Use Default Value Bridge opening area rating table Input as the elevation area pairs in ascending order The first data shall be the invert Datat Elevation fm Opening
6. 2 1973 1928 1693 1381 1158 916 572 257 34 11 o o cO OO OO 00000000 rQ 52 29 69 55 10 63 97 37 68 10 2s 84 47 00 00 00 00 00 00 00 oo 00 oo 00 00 oo 00 n P o o oo o mb Ph Ph Ph OO n m OO 953 154 222 277 351 484 668 884 145 455 780 083 345 559 726 848 919 934 766 552 210 671 738 807 349 494 Basin Area sf 18686296 18134795 17555526 16952047 16331143 15726982 15155474 14600292 14065443 13573553 13119712 12673790 12214771 11729334 11215577 10673862 10003454 9275724 3500203 7670142 6775297 5799489 4715126 3468251 1919726 541655 534779 524198 Oo MO SG GA Oh AF oO On JOJON w o WD WD Dm JONN Flow Area av sf 588 588 588 588 588 585 578 568 559 549 539 529 519 510 500 490 481 471 462 445 436 428 420 412 405 398 391 oo oo oo oo oo 60 43 ER 10 33 51 69 ER 10 39 77 28 93 76 Bridge V ft s 3 066 Remark der ft MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 19 Please note that the highest flow velocity of 6 9 fps occurs at time 7 6 hours underlined row above when the downstream tide elevation is at an elevation of 0 84 feet The channel bed elevation is at 6 8 feet so the downstream flow
7. 73 16 0 00 4 738 1919726 7 9 00 0 103 sc LS 682 75 0 00 2 807 541655 6 9 20 0 216 0 200 83 44 0 00 0 349 534779 3 9 40 0 322 0 331 116 03 0 00 0 494 524198 4 MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 16 OUTPUT RESULTS SKETCHES 10 10 Ea E 6 4 ta E SE E E 4 4 6 6 3 3 Elevation vs Bridge Opening Area 10 10 5 5 6 6 g 8 bk E ch 8 2 4 4 6 6 8 45 Elevation vs Basin Surface Area MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 17 Tidal and Riverine Hydrographs For this case the user selected a riverine hydrograph with a constant discharge Headwater Tailwater Relationships at Bridge Note that the velocity of flow thorough the bridge is highest When the head differential across the bridge is greatest MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 18 Evaluating Scour Computations At Tidal Bridges HEC RAS TIDAL COMPUTATIONS Two flow conditions should be checked for each combination of riverine and storm tide discharges to be evaluated 1 2 The riverine discharge with low tide elevation The combination of riverine and maximum storm tide discharges at mid tide elevation Note that the maximum storm tide discharge can be estimated as Q max 3 14 VOL T Where VOL volume of water in the tidal prism between high and low tides T tidal period selected as 24 hours for the Chesapeak
8. 8 for computing the TR 20 hydrograph For drainage areas greater than 300 square miles use the U S Geological Survey USGS dimensionless hydrograph described in USGS Water Resources Investigations Report 97 4279 The use of this approach should be discussed with the Office of Structures prior to the commencement of the tidal study 1 If the drainage area for the 100 year riverine hydrograph is less than 25 square miles assume that the peak riverine discharge and the peak storm surge elevation occur at the same time match the peaks of the hydrographs 2 If the time of concentration of the 100 year riverine hydrograph is more than 24 hours treat the storm tide and riverine flood as independent events To evaluate the effects of the 100 year riverine hydrograph separately use a tidal hydrograph with a tidal period of 24 hours and an average tidal condition having a range between mean lower low water and mean higher high water This essentially provides a low tailwater condition for evaluating scour at the bridge 3 If 1 the drainage area is over 25 square miles and 2 the time of concentration of the riverine hydrograph is less than 24 hours then compute the riverine discharge as a constant discharge The recommended approach for the TIDEROUT 2 analysis is to start the routing procedure for the combined riverine and tidal flows assuming the tidal basin MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 6 is full Fo
9. EROUT2 USERS MANUAL MAY 2015 Page 8 Tools Utility tools for quick calculations Help Help menus to answer questions about the program F 1 Short Help Help for any input window can be obtained by placing the cursor in the input field window and clicking on the F1 Key 2 TAB BARS A PROJECT DATA Project Describe the highway and the estuary being crossed include information on particular aspects of the study i e flood discharges referenced tidal station etc Unit option SHA prefers English units Analysis starting time For the Chesapeake Bay the storm tide period is assumed to be 24 hours Typically the worst case scour is expected to occur during the 12 hour ebb tide period starting when the tidal basin is full high tide and at the elevation of the design storm tide time 0 hours and ending when the basin has emptied time 12 hours Analysis ending time 12 at low tide Time step See Fl Starting bridge headwater elevation High tide elevation of the design storm tide or See F1 guidance Tide amplitude See Fl Tidal period Default value is 24 hours Tidal peak time hrs is Zero Please click on and read the Disclaimer button MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 9 STREAM FLOW DATA TIDEROUT2 C 2008 old stuff on tidal hydraulics 2008 fred tidal presentation EXAMPLE 1 4_11_08 tid PE Fie Run Draw Tools Help Project Data Stream Flow data Tidal Basin Data
10. OFFICE OF STRUCTURES STRUCTURE HYDROLOGY AND HYDRAULICS DIVISION CHAPTER 11 APPENDIX B TIDEROUT2 USERS MANUAL Version 2 Build 1 22 4 April 2015 MAY 2015 TABLE OF CONTENTS o A a O E e E E E E EE 3 Introductions bebe 5 KT 5 Boundary Cond OS siii tr ida 5 Combining Riverine and Storm Tide Dscharges 6 GEHEIERT AE E 7 Input Data tor TIDEROUT eebe Aa iia 8 Program A e EE 14 Scour Computations at Tidal Bndees 0 ccc ccc cece ence eee esser eee enae ena eees 20 MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 2 Preface TIDEROUT 2 Build 1 22 4 dated April 2015 is the current version of this program and all previous versions should be discarded The user is advised to check the web site below for any revisions to the program http www gishydro eng umd edu The material presented in this TIDEROUT 2 Users Manual has been carefully researched and evaluated It is periodically updated and improved to incorporate the results of new research and technology However no warranty expressed or implied is made on the contents of this program or the user s manual The distribution of this information does not constitute responsibility by the Maryland State Highway Administration or any contributors for omissions errors or possible misinterpretations that may result from the use or interpretation of the materials contained herein TIDEROUT 2 is a flood routing program Its primary purpose is to serve to estimate scou
11. OUT2 USERS MANUAL MAY 2015 Page 15 OUTPUT PRINTOUT PART 2 TIDEROUT COMPUTATIONS Note Remark show critical depth for critical flow with indicates fail to converge after 100 cycles Time Tide EL Basin EL Bridge Q Weir Q Bridge V Basin Area Flow Area Remark hrs ft ft av cfs av cfs ft s sf av sf der ft 0 00 5 240 5 240 0 00 0 00 0 000 19000000 0 588 00 0 20 5 236 5 238 84 99 0 65 0 241 19000000 0 588 00 0 40 5 223 5 231 195 32 7 88 0 554 19000000 0 588 00 0 60 5 201 5 218 313 22 32 50 0 888 19000000 0 588 00 0 80 5 172 5 200 424 62 80 96 1 204 19000000 0 588 00 1 00 5 133 5 175 527 98 155 65 1 497 19000000 0 588 00 1 20 5 087 5 142 622 54 255 15 1 765 19000000 0 588 00 1 40 5 032 5 102 708 16 375 58 2 007 19000000 0 588 00 1 60 4 969 5 053 785 19 511 95 2 226 19000000 0 588 00 1 80 4 899 4 997 854 45 657 22 2 422 19000000 0 588 00 2 00 4 821 4 932 916 93 807 70 2 599 19000000 0 588 00 2 20 4 735 4 860 973 70 957 74 2 760 19000000 0 588 00 2 40 4 642 4 780 1025 54 1109 41 2 907 19000000 0 588 00 2 60 4 542 4 692 1073 00 1257 98 3 041 19000000 0 588 00 2 80 4 436 4 597 1116 71 1403 00 3 165 19000000 0 588 00 3 00 4 323 4 496 1158 01 1528 75 3 282 19000000 0 588 00 3 20 4 204 4 391 1200 28 1609 98 3 402 19000000 0 588 00 3 40 4 080 4 281 1246 07 1671 13 3 532 19000000 0 588 00 3 60 3 950 4 168 1296 09 1708 24 3 674 19000000 0 588 00 3 80 3 815 4 050 1347 54 1787 06 3 820 19000000 0 588 00 q ac rage B
12. R mn nn nnn rn nnn nnn Time Tide EL Basin EL Bridge Q Weir Q Bridge V Basin Area Flow Area Remark hrs ft ft av cfs av cfs ft s sf av sf der ft 4 00 3 675 3 925 1394 72 1882 52 3 953 18686296 2 588 00 4 20 3 531 3 794 1434 33 1943 29 4 066 18134795 2 588 00 4 40 3 383 3 656 1465 68 1972 69 4 154 17555526 3 588 00 4 60 3 232 3 512 1489 67 1973 55 4 222 16952047 7 588 00 4 80 3 077 3 365 1508 84 1928 10 4 277 16331143 4 588 00 5 00 2 920 3 221 1528 80 1693 63 4 351 15726982 5 585 60 5 20 2 761 3 085 1556 27 1381 97 4 484 15155474 9 578 43 5 40 2 600 2 952 1593 09 1158 37 4 668 14600292 9 568 81 5 60 2 437 2 825 1638 35 916 68 4 8394 14065443 3 559 10 5 80 2 274 2 708 1695 81 572 10 5 145 13573553 9 549 33 6 00 2 110 2 600 1765 81 257 25 5 455 13119712 2 539 51 6 20 1 946 2 494 1836 93 84 34 5 780 12673790 4 529 69 6 40 1 783 2 384 1897 47 11 47 6 083 12214771 7 519 87 6 60 1 620 2 269 1941 85 0 00 6 345 11729334 9 510 10 6 80 1 459 2 147 1969 09 0 00 6 559 11215577 7 500 39 7 00 1 300 2 018 1980 62 0 00 6 726 10673862 0 490 77 7 20 1 143 1 881 1977 36 0 00 6 848 10003454 7 481 28 7 40 0 988 1 736 1959 11 0 00 6 919 9275724 7 471 93 7 60 0 837 1 582 1925 33 0 00 6 934 8500203 5 462 76 0 9 Y 1875 D 7 7670142 0 gt 3 8 00 0 545 1 239 1806 58 0 00 6 766 6775297 2 8 20 0 405 1 045 1715 94 0 00 6 552 5799489 0 8 40 0 270 0 829 1595 84 0 00 6 210 4715126 3 8 60 0 140 0 581 1430 26 0 00 5 671 3468251 1 8 80 0 016 0 272 11
13. e Bay and The HEC RAS results can be used as input to ABSCOUR 9 to develop an evaluation of scour at the bridge TIDEROUT SCOUR COMPUTATIONS The clear water scour equation Refer to the ABSCOUR 9 Users Manual in Chapter 11 is used to estimate scour from the TIDEROUT 2 output tables A portion of the table depicting flow through the bridge vs time is excerpted below Time hrs 4 20 40 60 80 00 20 40 w w o o o o oi 32 2 AA OO Oh Om o OKO Dm bb as oo 40 60 80 00 20 40 60 30 00 20 40 60 00 20 40 60 80 00 20 40 ft 675 531 383 232 077 320 761 600 437 274 110 946 783 620 459 300 143 988 837 OOrFRPRrFRFRFRFREFN NN NNN oO oO WOW Ww 645 405 270 140 016 0 103 0 216 0 322 ooo o og Wach 925 794 656 512 365 221 085 952 825 708 600 494 384 269 147 018 881 736 582Z 239 045 829 581 272 0 115 0 200 0 331 OO Ott fr Grp NN NNN NNN oO Go WWW WW Tide EL Basin EL Bridge Q av cfs 1394 1434 1465 1489 1508 1528 1556 1593 1638 1695 1765 1836 1897 1941 1969 1980 1977 1959 1925 875 72 33 68 67 84 80 2 09 35 81 81 93 47 85 og 62 36 11 33 5 13 183806 1715 1595 1430 1173 682 58 94 84 26 16 75 83 44 116 03 Wei av cfs 1882 1943 197
14. ement of sediment through the tidal basin 2 Method cannot be used for complex tidal currents resulting from flows between islands where wind forces predominate 3 User needs to separately compute contraction and local abutment scour 4 User needs to import TIDEROUT2 output into ABSCOUR to compute pier scour MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 4 Introduction Chapter 10 Appendix A Hydraulics of Tidal Bridges provides a comprehensive discussion of various aspects of the hydraulic design of tidal bridges The user of the TIDEROUT 2 program is encouraged to become familiar with the guidance in Chapter 10 Appendix A before conducting a tidal analysis at a bridge The user needs to recognize that unsteady tidal flow is complex and that TIDEROUT 2 provides for simple hydraulic and scour models to evaluate it Nevertheless the program can be used effectively in the design of structure foundations to evaluate and determine worst case scour conditions Tide Models The Office of Structures currently uses TIDEROUT 2 and HEC RAS to analyze tidal flow at a bridge Two dimensional flow models are useful for evaluating flow in large estuaries but are not considered necessary for the typical SHA tidal crossing The SHA guidance is geared towards tidal areas tributary to the Chesapeake Bay Special studies may be necessary for estuaries discharging directly to the ocean The following guidance is provided with regard t
15. g the feasibility of constructing a scour module for TIDEROUT 2 that would compute contraction scour on a step by step basis This approach should add to the accuracy of the estimated scour computed for tidal bridges Input Data for TIDEROUT 2 Typical input values are described below Tidal elevations for use in the analysis will depend on the location of the structure and other factors The user may wish to select other values depending on the issues to be addressed PROJECT DATA TIDEROUT2 C 2008 old stuff on tidal hydraulics 2008 fred tidal presentation EXAMPLE 1 4_11_08 tid aE Fie Run Draw Tools Help Project Data Stream Flow data Tidal Basin Data Bridge Opening Data Roadway Data Output Graphic Project WALLACE Creek no wind setup 32ft span overtopping 100 yr 4_01_2008 Unit option E gt C Metric SI units Analysis starting time hr H Analysis ending time hr 12 Time step hr 2 Starting bridge headwater elevation fm 5 24 Leave blank for default condition Press lt F1 gt for detail Tidal amplitude fm 313 Mean tidal elevation firm 211 Tidal period hr 24 DISCLAIMER Tidal Peak Time hr 0 TIDEROUT 2 opens to the Project Data Card This card has the following characteristics 1 TOOL BAR e File File management including accessing and saving TIDEROUT 2 files e Run Run the program e Draw Draws a schematic of the output results MD SHA OFFICE OF STRUCTURES TID
16. include a pier in the waterway the above information can be input in the pier module in ABSCOUR 10 to compute the pier scour Modified Neill s Curve for Non cohesive Soils in the Piedmont Region See Chapter 11 for Cohesive Soils 100 10 Critical Velocity fps MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 21
17. o selection of a tidal model for Chesapeake Bay estuaries Most likely a typical bridge site will not exhibit the clear cut categories listed below and judgment will be needed to select the most appropriate model It may be helpful to use both models compare the results and then select the most appropriate results TIDEROUT 2 HEC RAS Tidal crossing in close proximity to the bay A Tide elevations control downstream tailwater elevations Tidal crossing at a considerable distance X from the outlet to the bay Downstream tailwater controlled by normal depth Manning considerations Small riverine discharge tidal flow X predominates Large upland drainage basin riverine X discharge predominates Boundary Conditions for TIDEROUT 2 During a major storm such as a hurricane there are two different events that need to be considered in evaluating flow through a tidal bridge and the resulting scour at the foundations One event is the discharge through the bridge caused by the storm tide and the other related event is the riverine discharge through the bridge caused by the heavy rains on the upland drainage basin The peak discharges from these two events may or may not occur at the same MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 5 time There is no standard or correct way of evaluating these flows since each tidal bridge will present a different set of conditions to consider H
18. owever the Office of Structures recommends that the following procedure be followed as a guide in deciding how to combine the upland riverine flow with the storm tide flow A preliminary meeting with the Office of Structures is recommended to discuss the tidal conditions The results of this approach also need to be discussed with the Office of Structures to determine whether the computed discharges are reasonable If an alternative scenario is determined to offer a better approach the alternative method should be discussed with the Office of Structures prior to the commencement of the tidal study Combining Riverine And Storm Tide Discharges 100 Year Combined Riverine And Storm Tide Discharges It has been the experience of the Office of Structures that determining the relative timing of the occurrence of the peak riverine flow with the timing of the peak tidal surge is not subject to a rigorous analysis Many factors can influence the way in which these two peak flows will develop to form the peak flow conditions at the bridge The following guidance is based on previous studies conducted by the office of Structures However it may not be appropriate for all tidal crossings Estimate the 10 year and 100 year riverine hydrographs from the upland drainage basin Use the TR 20 dimensionless hydrograph in TIDEROUT 2 for drainage areas under 25 square miles If the drainage area is over 25 square miles follow the guidance in Chapter
19. ph option is selected there are two ways of inputting the data e fa hydrograph has already been developed as a part of a project study it can be manually input here MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 10 e The user can also click on the generate hydrograph button to obtain a TR 20 single area model A window is presented to input the hydrograph characteristics We note that the TR 20 peak factor constant is 484 for all of the physiographic regions in Maryland except for the Eastern Shore which is 284 The time step selected in normally 0 1 to 0 2 hours to be consistent with the tidal hydrograph e The user can shift the stream inflow hydrograph so that the peak riverine discharge coincides with the peak tidal flow elevation at time zero or with any other tidal flow elevation or discharge For example assume that the time of concentration of the riverine hydrograph peak occurs at time 19 hours and the user desires to shift the hydrograph so that this peak occurs at time zero for the tidal hydrograph This is accomplished in the following manner 1 compute the hydrograph and then 2 adjust the hydrograph time discharge pairs for each time unit to shift the hydrograph peak to the desired time In the example presented above the hydrograph would need to start at time 19 hours so that the peak flow would occur at time zero TIDE BASIN DATA l I U U L 1 1 L 1 1 l 1 i insert
20. r and mean higher high water This essentially provides a low tailwater condition for evaluating scour at the bridge If 1 the drainage area is over 25 square miles and 2 the time of concentration of the riverine hydrograph is less than 24 hours then evaluate the 500 year tidal storm surge and compute the riverine discharge as a constant discharge equal in value to the 2 year peak discharge Other Considerations Tidal flow is complex especially if a combination of riverine and tidal discharges is to be used in the analysis In low lying tidal basins particularly on the Eastern shore the tidal basin boundary elevations may be at four feet or less while the storm tide elevations may be at six feet or more Careful analysis is needed to decide the proportion of the flows going through the bridge over the road and across the drainage divide to other watersheds FEMA maps which are commonly used to define peak storm tide elevations are based on the NGVD datum of 1929 while SHA current project mapping is based on NAVD datum of 1988 The user will need to convert tidal data from the NGVD datum to NAVD datum when using the program See Chapter 10 Appendix A MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 7 e Various other factors such as the wind may influence the flow through the bridge Please refer to Chapter 10 Appendix A for a discussion of these factors e The Office of Structures in currently evaluatin
21. r at bridges in tidal waterways It can be used to route riverine flows from an upland watershed down to the tidal basin and then route the combined riverine tidal flow through the bridge and perhaps over the road down to the sea e Basic equation Inflow Outflow Storage e Bridge flow roadway overtopping flow tidal flow riverine flow Many newly designed tidal bridges span wetlands and do not constrict tidal flow so as to cause significant contraction scour Contraction scour may be more of a problem with older structures that do constrict the waterway area Please refer to the Introduction to this Appendix for a discussion of the advantages of using both the Tiderout 2 and the HEC RAS program for determining the worst case conditions for scour The advantages of the TIDEROUT program include 1 Takes into account conditions of unsteady tidal flow 2 Evaluates potential benefits of storage in the tidal basin upstream of structure 3 Provides a means of combining riverine and tidal flow hydrographs to estimate the worst case scour condition 4 The user can very quickly change input parameters to do sensitivity testing of reasonable combinations of storm tides riverine flow wind conditions etc to find the worst case scour MD SHA OFFICE OF STRUCTURES TIDEROUT2 USERS MANUAL MAY 2015 Page 3 The limitations of the TIDEROUT 2 program include 1 Method does not address other aspects of tidal flow such as littoral drift or mov
22. r this condition use a constant riverine discharge equal to the 10 year peak discharge cfs 500 Year Combined Riverine And Storm Tide Discharges Estimate the 2 year and 500 year riverine hydrographs from the upland drainage basin Also estimate the 10 year hydrograph if not already computed for the 100 year combined riverine and storm tide discharge Use the SCS dimensionless hydrograph in TIDEROUT 2 for drainage areas under 25 square miles If the drainage area is over 25 square miles follow the guidance in Chapter 8 for computing the TR 20 hydrograph For drainage areas greater than 300 square miles use the U S Geological Survey USGS dimensionless hydrograph described in USGS Water Resources Investigations Report 97 4279 The use of this approach should be discussed with the Office of Structures prior to the commencement of the tidal study l If the drainage area for the 500 year riverine hydrograph is less than 25 square miles use TIDEROUT 2 to compute the flow of the 500 year tidal storm surge through the bridge Use a constant discharge value for the riverine flow equal to the 10 year peak discharge If the time of concentration of the 500 year riverine hydrograph is more than 24 hours treat the storm tide and riverine flood as independent events To evaluate the 500 year riverine hydrograph separately use a tidal hydrograph with a tidal period of 24 hours and an average tidal condition having a range between mean lower low wate
Download Pdf Manuals
Related Search