/ DIY Bridge #101
We built a low water bridge at the local non-profit camp and the leader decided (against a lot of advice, but he knew better) to put in ten 12" diameter X 8' long concrete pipes to save money. Creak is ~18' wide with very little to no slope, and dry most of the year. 5 years later its a low water dam.If you are going to dig the creek bed for a bridge that's probably fine but for culverts, I would advise against it will only fill back up with sediments and your culvert will end up half full of dirt within a few years...
We built a low water bridge at the local non-profit camp and the leader decided (against a lot of advice, but he knew better) to put in ten 12" diameter X 8' long concrete pipes to save money. Creak is ~18' wide with very little to no slope, and dry most of the year. 5 years later its a low water dam.
You need the right amount of slope and big enough diameter so that the flow can/will flush the sticks and debris out.
Dittos in Sierra foothills and all up and down the San Joaquin Valley ....Now that we're finally getting too much rain here in California all at once I'm glad I have a bridge with lots of clearance (8' high and 48'wide). My creek went from being ankle deep and 8' wide to up 5' deep and 35' wide on several occasions in the last month. As far as the idea of letting water over flow a hard surface or coming out of a culvert, I've seen what I call the "waterfall effect" where the running water scours out the downstream side of the discharge point eroding the creek bed when experiencing high flows. Often it may fill back up with silt when the fast flowing water subsides but often leaves of hole, or a pool, check out county culverts in your area. Also I've seen where the displaced material can create a sandbar barrier that further down that also alters the flow to one side or the other downstream. Whatever you decide, I like that quote from a movie of Morgan Freeman, " Go big or go home"!
“If the terrain allows it, build relief dips on both sides of the bridge.” This sounds like a good idea. Certainly something to look into. Thanks.In a 50-yr career building stream crossings for 100K lb log trucks I learned that bridges are always better than culverts. They take more careful planning and are more expensive to build initially, but they will always pass more water--and with less impact--than culverts. If the terrain in your case will allow it, build relief dips on both sides of the bridge. When the flood waters get high enough to lap at the bottom of the bridge you want them to continue downstream by going around the bridge, not over it. When the water subsides it will be much easier and cheaper to repair the eroded roadway on both sides of the bridge than repairing the bridge itself.