(CRAM) For Wetlands User's Manual Version 5.0.2

California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 4
Table 4.11b: Rating of Hydroperiod for Individual Vernal Pools and Pool Systems.
Rating
A
B
C
D
Alternative States
(based on Table 4.10 above)
Hydroperiod of the AA is characterized by natural patterns of filling,
inundation, or saturation as well as natural patterns of drying or drawdown
with no indication of hydro-modification. There are no artificial controls on
the hydroperiod.
The filling, inundation, or saturation patterns in the AA are of greater
magnitude or longer duration than would be expected under natural condition
(or compared to comparable natural wetlands), but thereafter, the AA is subject
to natural processes and patterns of drawdown or drying.
The patterns of filling, inundation or saturation of the AA as well as the
patterns of drawdown or drying of the AA are naturalistic but controlled by
unnatural processes due to hydromodification.
The patterns of filling, inundation or saturation of the AA as well as the
patterns of drawdown or drying of the AA significantly deviate from natural
patterns due to hydromodification.
Perennial Estuarine: The volume of water that flows into and out of an
estuarine wetland is termed the “tidal prism.”
The tidal prism consists of inputs from both tidal (i.e., marine or estuarine) and
non-tidal (e.g., fluvial or upland) sources. The timing, duration, and frequency
of inundation of the wetland by these waters are collectively referred to as the
tidal hydroperiod.
Under natural conditions, increases in tidal prism tend to cause increases in
inorganic sedimentation, which raises the tidal elevation of the wetland and
thus reduces its hydroperiod. If the sediment supply is adequate, estuarine
marshes tend to build upward in quasi-equilibrium with sea level rise.
A change in the hydroperiod of an estuarine wetland (i.e., a change in the tidal
prism) can be inferred from changes in channel morphology, drainage network
density, and the relative abundance of plants indicative of either high or low
tidal marsh. A preponderance of shrink-swell cracks or dried pannes on the
wetland plain is indicative of decreased hydroperiod. In addition, inadequate
tidal flushing may be indicated by algal blooms or by encroachment of
freshwater vegetation. Dikes, levees, ponds, or ditches are indicators of an
altered hydroperiod resulting from management for flood control, salt
production, waterfowl hunting, mosquito control, etc. Table 4.12 provides
narratives for rating Hydroperiod for perennial estuarine wetlands.
Seasonal Estuarine: The hydroperiod of a seasonal estuarine wetland can be
highly variable due to inter-annual variations in freshwater inputs and
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