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

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California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 4 Rating A B C D Table 4.14: Rating for Riverine Channel Stability. Alternative State (based on worksheet above) Most of the channel through the AA is characterized by equilibrium conditions, with little evidence of aggradation or degradation (based on the field indicators listed in worksheet). Most of the channel through the AA is characterized by some aggradation or degradation, none of which is severe, and the channel seems to be approaching an equilibrium form (based on the field indicators listed in worksheet). There is evidence of severe aggradation or degradation of most of the channel through the AA (based on the field indicators listed in worksheet), or the channel is artificially hardened through less than half of the AA. The channel is concrete or otherwise artificially hardened through most of AA. 4.2.3 Hydrologic Connectivity A. Definition: Hydrologic Connectivity describes the ability of water to flow into or out of the wetland, or to accommodate rising flood waters without persistent changes in water level that can result in stress to wetland plants and animals. This metric pertains only to Riverine, Estuarine, Vernal Pool Systems, Individual Vernal Pools, Depressional, and Playas. B. Rationale: Hydrologic connectivity between wetlands and adjacent uplands promotes the exchange of water, sediment, nutrients, and organic carbon. Inputs of organic carbon are of great importance to ecosystem function. Litter and allochthanous input from adjacent uplands provides energy that subsidizes the aquatic food web (Roth 1966). Connection with adjacent water bodies promotes the import and export of water-borne materials, including nutrients. Hydrologic connections with shallow aquifers and hyporheic zones influence most wetland functions. Plant diversity tends to be positively correlated with connectivity between wetlands and natural uplands, and negatively correlated with increasing inter-wetland distances (Lopez et al. 2002). Amphibian diversity is directly correlated with connectivity between streams and their floodplains (Amoros and Bornette 2002). Linkages between aquatic and terrestrial habitats allow wetland-dependent species to move between habitats to complete life cycle requirements. This metric is scored by assessing the degree to which the lateral movement of flood waters or the associated upland transition zone of the AA and its encompassing wetland is restricted by unnatural features such as levees, sea walls, or road grades. For estuarine wetlands, the function of upland transitions as refuge for intertidal wildlife during extreme high tides is especially important C. Seasonality: This metric is not sensitive to seasonality. D. Field Indicators: Scoring of this metric is based solely on field indicators. Tables 4.14a–14c contain narratives for rating the Hydrologic Connectivity metric. 62
California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 4 Riverine: For riverine wetlands, Hydrologic Connectivity is assessed based on the degree of channel entrenchment (Leopold et al. 1964, Rosgen 1996, Montgomery and MacDonald 2002). Entrenchment calculated as the flood-prone width divided by the bankfull width. The flood-prone width is measured at the elevation equal to twice the maximum bankfull depth; maximum bankfull depth is the height of bankfull flow above the thalweg. The process for estimating entrenchment is outlined below. Worksheet 4.5: Riverine Wetland Entrenchment Ratio Calculation The following 5 steps should be conducted for each of 3 cross-sections located in the AA at the approximate mid-points along straight riffles or glides, away from deep pools or meander bends. Steps Replicate Cross-sections 1 2 3 1 Estimate bankfull width. 2: Estimate max. bankfull depth. 3: Estimate flood prone depth. 4: Estimate flood prone width. 5: Calculate entrenchment. 6: Calculate average entrenchment. This is a critical step requiring familiarity with field indicators of the bankfull contour. Estimate or measure the distance between the right and left bankfull contours. Imagine a level line between the right and left bankfull contours; estimate or measure the height of the line above the thalweg (the deepest part of the channel). Double the estimate of maximum bankfull depth from Step 2. Imagine a level line having a height equal to the flood prone depth from Step 3; note where the line intercepts the right and left banks; estimate or measure the length of this line. Divide the flood prone width (Step 4) by the bankfull width (Step 1). Calculate the average results for Step 5 for all 3 replicate cross-sections. Enter the average result here and use it in Tables 4.15 a, b. Flood Prone Width Bankfull Width Flood Prone Depth Bankfull Depth Figure 4.5: Parameters of Channel entrenchment. Flood prone depth is twice maximum bankfull depth. Entrenchment equals flood prone width divided by bankfull width. 63
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LIST OF WORKSHEETS Worksheet 4.1: L
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