BRIDGES Definition A Bridge is defined in Minnesota

BRIDGES

Definition � � A Bridge is defined in Minnesota as a structure over 10’ in length, sized hydraulically to convey water under a highway, railroad or other embankment Road grade, geometrics, sitedistance, vertical curvature or ecological considerations may also influence the size of the waterway opening

Basic Criteria � � For DNR- no stage increase over 0. 5’ for new crossings. Check flood damage potential upstream Velocities no more than 8 -9 fps Match the channel width up and down stream

Case Studies � Br 20558� ADT < 50, minimum flood is 5 year � Design speed: 30 mph � Sag Vertical Curve � Match the natural channel bottom � Used a 100 year design event as road profile drives the design

Case Studies � Br 85560 � ADT <50 (Dead End), minimum flood is 5 year � Inplace 4 - 36” CMP with Slab � Resident was cut off during floods, township wanted dry crossing � Road design 30 mph, design speed set the road profile � Max velocities between 8 -9 fps � Stage increase < 0. 5’ � Designated trout stream � 25 year design was used

Case Studies � Br 58552 � ADT < 50, minimum flood is 5 year � Sag Vertical Curve, design speed 30 mph � Old bridge was constricting the river � Channel Bottom Upstream and Downstream ~ 80’ wide � High debris stream � Vertical curve drives the design � Used a 100 year design event

Case Studies � Br 08552 � ADT 510 minimum flood is 25 year event � Road profile is driving the design � Inplace road does not overtop � Stage increase was to be held at a minimum 0. 6’ for the inplace 0. 5’ for the proposed � 100 year design was used

Case Studies � Br 30515 � ADT 925 minimum flood is 25 year � ARRA Project- Federal Funds were used � 55 mph design speed was required as ARRA funds were used � Sag Curve was designed for the design speed � Bridge sized to match natural channel bottom � 100 year design was used

Case Studies � Br 22605 � ADT < 50, 5 year event � Road Profile is driving the design � Matched the waterway opening of inplace bridge � Br 55583 � ADT 2200, 50 year minimum event � Velocities are high, 8. 5 fps � Match existing bridge lengths � 100 year design was used on both bridges

Deck Drains � � � Federal Requirement: Army Corps of Engineers General Permit does not allow bridges with over 500 heavy vehicles per day to drain directly to a trib to a navigable water No State Regulation, but DNR has conditions in the General Permit that will not allow direct drainage to a stream When ever possible, keep the deck drainage from being discharged directly to a stream