Regulated Rivers - Hydro-Environmental Analysis: Freshwater Environments - page 57

Red

Green

Gray

FIGURE 3.14 Illustration of the good (green), bad (gray), and ugly (red) culverts. (Courtesy of USDA Forest
Service, Alaska Division.)

One of the themes of this text is also “one generation's solution is the next generation's prob-
lem,” or for engineers perhaps the next generation's job. Today, engineers are commonly involved
in designing or retroitting culverts to make them more environmentally friendly. Guidance for the
design includes:

• FHWA Culvert repair practices manual, Volume 1 (FHWA 1995), pp. 3-58-3-61 and 5-39-

5-50, and Volume 2, Appendix B-23, for a discussion on ish passage and ish passage
devices

• NOAA Fisheries Draft: Culvert criteria for ish passage and the guidelines for salmonid

passage at stream crossings

• Washington (2003) “Design of road culverts for ish passage”

3.2.4 L eVeeS
Levees (as illustrated in Figure 3.15) are embankments that are primarily designed for lood protec-
tion from seasonal high waters with lood durations most commonly only a few days or weeks per
year. Even though levees are similar to small earth dams, they differ from earth dams in the follow-
ing important respects (USACE 2000):

• A levee embankment may become saturated for only a short period of time beyond the

limit of capillary saturation

• Levee alignment is dictated primarily by lood protection requirements, which often results

in construction on poor foundations

• Borrow is generally obtained from shallow pits or from channels excavated adjacent to the

levee, which produce ill material that is often heterogeneous and far from ideal.

Some levee types according to their use are shown in Table 3.1.