1. Basic Hydraulics: Bridges

2. Definition & terminology Abutments Flow contraction

3. Definition & terminology Bridge opening

4. Definition & terminology Piers in normal and skew crossings Obstruct flow Create instability

5. Bents, abutments, & embankments Abutments: Protective measures used at abutments consist of the following: riprap header slopes and deep toe walls (stone protection is generally preferred to vertical abutment walls sheet pile toe walls deep foundations of piles or drilled shafts Revetment is usually placed at the abutment on the slopes under the bridge end and around the corners of the embankment to guard against progressive embankment erosion

6. Bents, abutments, & embankments Two common types of revetments used to protect abutments are rigid (concrete riprap) and flexible (stone protection).

7. Bents, abutments, & embankments Embankments: Embankments that encroach on floodplains are most commonly subjected to scour and erosion damage by overflow and by flow directed along the embankment to the waterway openings The embankment may need to be protected if significant overtopping of the approach embankment is anticipated during the life of the crossing The embankment can be protected with soil cement or revetments, rock, wire-enclosed rock, or concrete.

8. Contraction The contraction of flow caused by the bridge opening (and piers) increases velocities in the contraction. The contraction also causes a backwater drawdown (in subcritical flow)

9. Bridge scour A scour analysis is required for new bridges, replacements, and widenings Where a scour analysis indicates high depths of potential contraction scour, a structure larger than that required by the basic velocity and backwater criteria may be more cost effective than to designing foundations and armoring to withstand the scour The potential for deep local scour can be reduced by enlarging the structure, but designing foundations and armoring to withstand local scour depths may be more cost-effective.

10. Bridge scour USGS

11. Scour at highway bridges Three areas at bridges are affected by scour: At pier and abutment foundations. Commonly water flows faster around piers and abutments, making them susceptible to local scour Across a bridge opening. Contraction scour occurs when water accelerates as it flows through a bridge opening that is narrower than channel and floodplain upstream from bridge Throughout a long reach of the stream, both upstream and downstream of the bridge. This degradation in a stream is usually a long-term process that results in lowering the streambed.

12. Hydraulics as pre-requisite Determine backwater caused by the bridge abutments and piers Determine flow distribution and velocities Estimate scour potential HDM Chapter 9 Culvert Design and Analysis is subject of DES604

13. Hydraulics as pre-requisite Generally use computer models WSPRO HEC-RAS Flow Zones Loss methods in Zone 2 HDM 9-20

14. Hydraulics as pre-requisite If water reaches the lower chord of the bridge, then pressure flow is used. Still have a free surface