Design Guidelines for Bridge, Culvert, Dip Crossing, Low-Flow Channel, and Other Design Topics

1. VIII. Overview Of Design Guidelines A. Bridge Design Tips: • Use Computerized step-backwater model such as HEC-2, HEC-RAS or WSPRO • Take cross sections 1) far downstream 2) at the face of the bridge 3) at the bridge opening 4) far upstream • Utilize guidance (such as Hydraulics of Bridge Waterways) produced by Federal Highway Administration and/or the U.S. Army Corps of Engineers • Utilize Scour Countermeasures: such as provision of deep toe-downs on bridge piers and abutments or construction of spur dikes and jetties • Meet minimum freeboard requirements listed in the literature See these resources: Various City/County Design Manuals and CCDC-01 (5.4), CCDM-99 (1005), CTDM-89 (9.5), FITD Class CD

2. Example Large Scale Bridge

3. Example Small Scale Bridge

4. VIII. Overview Of Design Guidelines B. Culvert Design Tips: • Consider Step-by-Step Procedures for Sizing Culverts • See Literature for Explanations/Equations of Culvert Hydraulics • Determine whether a culvert is under inlet or outlet control • See Guidance for Culvert Inlet/Outlet Design and Protection • Consider Countermeasures for Culvert Sedimentation and Erosion • See Nomographs to simplify equation solving • See guidanceequations to evaluate the appropriateness of using a culvert in lieu of a bridge • See guidance for culvert material selection See these resources: Various City/County Design Manuals and CCDC-01 (5.1 to 5.3),CCDM-99 (1001 to 1004), CTDM-89 (11), YCDM-98 (8.2 to 8.4), FITD Class CD

5. Example Small Culverts

6. Example Culvert Inlet and Outlet Protection

7. Example Culvert Inlet and Outlet Control Diagrams

8. Example Culvert Flow Types

9. Example Culvert Nomograph

10. VIII. Overview Of Design Guidelines C. Dip Crossing Design Tips: Definition: “Crossings of watercourses which are designed to allow drainage to flow across roadways at-grade are commonly referred to as either ‘at-grade’ or ‘dip’ crossings” (CTDM-89). • Design Dip Crossings to have a 4% minimum cross-slope to reduce roadway sedimentation • At a minimum, place a two-foot-deep cutoff wall along the upstream side of the dip crossing to protect against general scour • Place a minimum 3-foot-deep cutoff wall downstream of the dip crossing to protect against local scour and channel degradation See these resources: Various City/County Design Manuals, CTDM-89, FITD Class CD

11. Examples of Dip Crossings

12. VIII. Overview Of Design Guidelines D. Low-Flow Channel Crossing Design Tips: Definition: When “the bottom of the channel cross section is too wide to efficiently convey the low-flow discharges [which instead] creates an incised low-flow channel that may meander back and forth across the bed of the channel...” And, “the meandering process can cause frequent and unnecessary scouring at the toe of the primary banks…[which can] even destabilize totally lined channels.” (CTDM-89). • Possibly construct a low-flow channel within any larger channel in order to restrict the low flows to a designated area within the primary channel. • The designed low-flow channel should be designed such that the unit discharge associated with the 2-year storm event is the same as pre-construction conditions. See these resources: Various City/County Design Manuals, CTDM-89, FITD Class CD

13. Example Low Flow Channel

14. VIII. Overview Of Design Guidelines E. Other Design Topics Design Guidance are Similarly Available for the Following – • Levee Systems See this resources: FITD Class CD

15. VIII. Overview Of Design Guidelines E. Other Design Topics • Levee System: Illustration Streams with well-developed natural levees tend to be of constant width and have low rates of lateral migration. Well-developed levees usually occur along the lower courses of streams or where the floodplain is submerged for several weeks or months a year. If the levee is breached, the stream course may change through the breach.

16. VIII. Overview Of Design Guidelines E. Other Design Topics Design Guidance are Similarly Available for the Following – • Levee Systems • FEMA Requirements See this resources: FITD Class CD

17. VIII. Overview Of Design Guidelines E. Other Design Topics Design Guidance are Similarly Available for the Following – • Levee Systems • FEMA Requirements • Channelization See this resources: FITD Class CD

18. ChannelizationIllustration

19. VIII. Overview Of Design Guidelines E. Other Design Topics Design Guidance are Similarly Available for the Following – • Levee Systems • Channelization • Super-Elevation See this resources: FITD Class CD

20. VIII. Overview Of Design Guidelines E. Other Design Topics • Levee System • Channelization • Super-Elevation:Illustrations Because of the change in flow direction which results in centrifugal forces, there is a superelevation of the water surface in bends. The water surface is higher at the concave bank than the convex bank.