California Rapid Assessment Method for Wetlands - State Water ...

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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 58
California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 4 occasional breaching of the tidal barrier. Assessing hydroperiod for seasonal estuaries requires knowing its recent history of inlet closure and opening. Hydroperiod alteration can be inferred from atypical wetting and drying patterns along the shoreline (e.g., a preponderance of shrink-swell cracks or dried pannes). Inadequate tidal flushing, or, in arid systems, excessive freshwater input during the dry season may be indicated by algal blooms or by encroachment of freshwater vegetation. Dikes, levees, ponds, ditches, and tide-control structures are indicators of an altered hydroperiod resulting from management for flood control, salt production, waterfowl hunting, mosquito control, boating, etc. Table 4.13 provides narratives for rating Hydroperiod for seasonal estuarine wetlands. Table 4.12: Rating of Hydroperiod for Perennial Estuarine wetlands. Rating A B C D Alternative States AA is subject to the full tidal prism, with two daily tidal minima and maxima. AA is subject to reduced, or muted, tidal prism, although two daily minima and maxima are observed. AA is subject to muted tidal prism, with tidal fluctuations evident only in relation to extreme daily highs or spring tides. AA is subject to muted tidal prism, plus there is inadequate drainage, such that the marsh plain tends to remain flooded during low tide. Table 4.13: Rating of Hydroperiod for Seasonal Estuarine wetlands. Rating A B C D Alternative States AA is subject to natural inter-annual tidal fluctuations (range may be severely muted or vary seasonally), and episodically has tidal inputs by natural breaching due to either fluvial flooding or storm surge. AA is subject to tidal inputs more often than would be expected under natural circumstances, because of artificial breaching of the tidal inlet. AA is subject to tidal inputs less often than would be expected under natural circumstances due to management of the inlet to prevent its opening. AA is rarely subject to natural tidal inputs. 59
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