(CRAM) For Wetlands User's Manual Version 5.0.2
(CRAM) For Wetlands User's Manual Version 5.0.2
(CRAM) For Wetlands User's Manual Version 5.0.2
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California Rapid Assessment Method for <strong>Wetlands</strong> v. <strong>5.0.2</strong> – Chapter 3<br />
3.2.2.1.1 Non-confined Riverine Sub-type<br />
In non-confined riverine systems, the width of the valley across which the system can migrate<br />
without encountering a hillside, high terrace, or other feature that is likely to resist migration is at<br />
least twice the average bankfull width of the channel. Non-confined riverine systems typically<br />
occur on alluvial fans, deltas in lakes, and along broad valleys. A channel can be confined by<br />
substantial artificial levees if the average distance across the channel at bankfull is more than half<br />
the distance between the levees. This assumes that the channel would not be allowed to migrate<br />
past the levees, and that levee breaches will be repaired. Confinement is unrelated to the channel<br />
entrenchment. Entrenched channels can be confined or non-confined (Figure 3.3).<br />
3.2.2.1.2 Confined Riverine Sub-type<br />
In confined riverine systems, the width of the valley across which the system can migrate<br />
without encountering a hillside, terrace, or substantial man-made levee is less than twice the<br />
average bankfull width of the channel. A channel can be confined by artificial levees and urban<br />
development if the average distance across the channel at bankfull is more than half the distance<br />
between the levees or more than half the width of the non-urbanized lands that border the<br />
stream course. This assumes that the channel would not be allowed to migrate past the levees<br />
and that levee breaches will be repaired. Confinement is unrelated to channel entrenchment.<br />
Entrenched channels can be confined or non-confined (Figure 3.3).<br />
3.2.2.2 Depressional <strong>Wetlands</strong><br />
Depressional wetlands exist in topographic lows that do not usually have outgoing surface<br />
drainage except during extreme flood events or heavy rainfall. Precipitation is their main source<br />
of water. Depressional wetlands can have distinct or indistinct boundaries. Many depressional<br />
wetlands are seasonal, and some lack surface ponding or saturated conditions during dry years.<br />
A complex of shallows and seasonally wet swales and depressions created by the slight<br />
topographic relief of a vernal pool system is an example of an indistinct depressional wetland.<br />
The margins of distinct depressional wetlands are relatively easy to discern in aerial photos and<br />
in the field. Examples of distinct depressional wetlands include sag ponds, snowmelt ponds,<br />
kettle-holes in moraines, cutoff ox-bows on floodplains, and water hazards on golf courses.<br />
3.2.2.2.1 Vernal Pool <strong>Wetlands</strong><br />
Vernal pools are ephemeral wetlands that form in shallow depressions underlain by bedrock or<br />
by an impervious, near-surface soil horizon (Witham 2006). These depressions fill with<br />
rainwater and runoff during the winter and may remain inundated until spring or early summer,<br />
sometimes filling and emptying repeatedly during the wet season (USFWS 1994). Vernal pools<br />
undergo four distinct annual phases: (1) the wetting phase with the onset of the first rains; (2)<br />
the aquatic phase when the peak rainfall and inundation occurs; (3) the drying phase when many<br />
plants flower and produce seed and many animals disperse; and finally (4) the drought phase<br />
when the soil dries and cracks, and the plants succumb to extreme dry conditions (Zedler 1987).<br />
Vernal pools typically support a minimum of 30% cover of native plant species during the<br />
aquatic or drying phase. Vernal pools in disturbed areas or ones that are subjected to abnormal<br />
rainfall patterns might not meet this criterion due to invasion by non-native plants (USFWS<br />
1994). If the wetland is mostly characteristic of a vernal pool but also has characteristics of other<br />
kinds of wetlands, such that its classification as a vernal pool is not completely certain, then it<br />
should be considered a vernal pool.<br />
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