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CLASSROOM ...
Index of topics:
Images: Forestry creek crossing structures
Summary: Images on this page show typical forestry creek crossing structures.
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Document: Estimating peak floods for the design of culverts and bridges for forest roads
Excerpt: The first step in designing a culvert or bridge for a particular location is to determine the design
flood. This is the flood that the culvert or bridge must be able to carry safely. This involves first
choosing the return period for the design flood, which involves considerations of cost, risk,
consequences of failure, how to deal with uncertainty and so on. However, the BC Forest
Practices Code makes it relatively simple by specifying Q100 3 (the 100 year flood) as the design
flow. A permanent bridge must be able to pass Q100, with adequate freeboard and a culvert must
be able to pass it, with the water level water no higher than the top of the entrance to the culvert.
Q100 is the flow that, on average, is exceeded once in 100 years. This is a very conservative
requirement, which means that, the estimated design flow already has a fair margin of safety built
in to it.
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Document: River Systems
Summary: Rivers carry sediment and logs and other floating debris as well as water. They also provide
habitat and transportation corridors for fish. Log jams form on rivers in forested regions. These persist
for years and tend to trap logs and floating debris, preventing them form reaching culverts and bridges.
Culverts in particular are very vulnerable to blockage from floating debris. However, from time to time, at
intervals of about 30 years and up, very large floods occur in an area. These "clean out" logs, log jams
and sediment from the stream beds and allow the logs and the bed load to reach the culverts and bridges
and damage or destroy them. This suggests that culverts and bridges should be designed to carry floods
in the 30 to 50 year range, with no damage and also that the design should minimize damage in the event
of a major flood with its accompanying sediment and debris load.
View this document ...
Document: Basic Hydraulics
This document includes ...
- types of flow
- Manning Formula
- Critical vs Subcritical flow
View this document ...
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