748.7 Bridge Deck and Bridge End Drainage

Drainage may be from the bridge deck that has not drained through deck drains or from the roadway before encroachment onto the bridge deck. For either situation, the excess drainage water at the location of the approach area should be made to exit the approach area at the bridge ends effectively without eroding the bridge/roadway sideslopes.

748.7.1 Bridge Deck Drainage

Bridges are provided with a combination of slab drains on the bridge and drain basins, if required (see EPG 504 Concrete Approach Pavement), drain flumes or rock blanket off the bridge at the bridge ends to drain the bridge deck. Bridge Division will determine the placement of slab drains.

748.7.2 Bridge End Drainage

Bridge end drainage provisions should be considered on every bridge job. Bridge end drainage are provisions for conveying bridge deck and roadway discharge near the bridge ends away from the bridge without eroding embankment spill slopes and sideslopes. Some examples of when bridge end drainage provisions are most effective are for down-grade ends on sloped bridges, bridges in sag vertical curves, long and/or wide bridges, inside radius of superelevated and curved bridges, roadways with curbs and gutters leading up to a bridge end. Consideration should also be given to providing drain basins on the up-grade side of bridges where the roadway has curb and gutter, or the roadway is steeply sloped and/or wide, or it is the critical low side of a superelevated roadway and there is a possibility of a significant volume of water being carried onto the bridge.

The project core team should make recommendations at the bridge field check or on the bridge field check memorandum for handling drainage when submitting bridge survey reports for concurrence by the Bridge Division and the selection should be noted on the Bridge Memorandum.

Bridge end drainage provisions can include concrete spill slope protection and concrete slope aprons, drain basins, curbs, and sideslope drainage provisions which includes rock blanket or drain flumes, or a combination of these. (See Standard Plans 609.40 for details.)

748.7.3 Bridges on a Major Route

Because concrete approach pavement is required for bridges on a major route, the available use of drain basins, as needed, and as the only drainage conveyance at the bridge end is sufficient. Drain basins should be provided on the down-grade side of all bridges on major routes. Consideration should be given to providing drain basins on the up-grade side of bridges where the roadway has curb and gutter, or the roadway is steeply sloped and/or wide, or the it is the critical low side of a superelevated roadway and there is a possibility of a significant volume of water being carried onto the bridge. Where interchange ramps with curb are involved at the end of a bridge, consideration should be given to carrying bridge drainage along the ramp curb to an outlet on the ramp in lieu of using curb and gutter or drain basins at the concrete approach pavement. The drainage facility beyond the limits shown in the standard plans is designed to meet the existing conditions at the bridge involved and is generally shown on the culvert section sheets.

748.7.4 Bridges on a Minor or Low Volume Route

Because concrete approach pavement is not used for bridges on a minor or low volume route, drain basins are not available as an option for drainage conveyance and other methods must be used. Either rock blanket or drain flumes should be considered for this purpose in order to prevent sideslope erosion.

748.7.5 Concrete Spill Slope Protection and Concrete Aprons

Concrete spill slope protection and concrete aprons adjacent to bridge wings should be used together in accordance with EPG 611.3 Concrete Slope Protection in order to prevent spill slope erosion along embankment and along the bridge wings.

748.7.6 Drain Basins

Drain basins and Type A curbs are used only when necessary (refer to EPG 504 Concrete Approach Pavement). When a concrete Bridge Approach Slab (Major) is included on the plans, and only when required, the roadway items of drain basins and Type A curbs as part of the concrete approach pavement and as shown on Standard Plan 609.40 are also specified on the roadway plans. When a Bridge Approach Slab (Minor) is used, a method of moving drainage away from the bridge end other than drain basins will be necessary since concrete approach pavements are not used with these bridge approach slabs.

748.7.7 Curbs

All bridge approach slabs will have curbs to direct the drainage away from the bridge wings. Bridge approach slabs on major routes will use a 4” Type A curb for the full length of the slab and in accordance with the standard plans. Approach slabs on minor and low volume routes will use either a 4” Type A curb or a 4” Type S curb for a partial length of 5’-6” along either the concrete or asphalt slab respectively.

748.7.8 Sideslope Drainage Provisions

There are a couple of methods for protecting sideslopes for bridge run-off (drainage water), or protecting and channeling bridge run-off on sideslopes that should be considered and implemented: Rock Blanket (EPG 611.1 Rock Blanket) and Drain Flumes.

748.7.9 Type 2 Rock Blanket at Stream Crossings

Rock blanket can be wrapped around the side of the embankment fill and will provide the necessary protection of the sideslopes for stream crossings. The upper limit of sideslope protection is the same elevation as the elevation of the upper limit of the front slope protection. However, if bridge drainage onto the sideslopes is a concern, the elevation of the sideslope protection can be extended to the shoulder of the roadway along the length of the Bridge Approach Slab (Minor) for at least 8’-6” from the end of the bridge wing. It is important that Permanent Erosion Control Geotextile (PECG) be used with Type 2 Rock Blanket which is shown on the Standard Plans. Type 1 Rock Blanket may be used with consensus of the project core team.

748.7.10 Type 2 Rock Blanket at Grade Crossings

Rock blanket is generally not wrapped around the embankment fill as sideslope protection. If bridge drainage onto the sideslopes is a concern, bridge end drain flumes should be implemented and run from the side of the bridge approach slab to a lower more stable and less erodible embankment elevation ending in either a rock basin or drainage ditch.

748.7.11 Drain Flumes

Drain (Rock) flumes can be used for protecting the sideslopes and channeling water for the case when rock blanket is not required to be extended up to the elevation of the approach slab. This is an economical decision for which both options produce equal performance with respect to bridge end drainage. A Type 1 Rock Ditch Liner with PECG is used for this purpose. The length of drain flume can vary based on the elevation of the rock blanket on the sideslope.