WETLAND FUNCTIONAL ASSESSMENT

 

1. NEED FOR FUNCTIONAL ASSESSMENT

a. To assess mitigation ratios

b. To assess both losses in function and gains due to mitigation

 

2. FUNCTIONS USED

Three major categories: water quality, hydrology, habitat (see listing below)

 

3. APPLIED ASSESSMENT

a. Measurements taken before impact and estimated after

b. Reference wetlands function set at 1.0

c. Impacted and restored wetlands function compared to reference standard

 

4. ESTIMATING FUNCTIONS

Two sources of variation:

a. Natural variation should be accomodated in reference measurements

b. Changes due to impacts will be separable and detectable

 

5. BUILDING ASSESSMENT MODELS

a. Measurable indicator variables are combined into indices of function

b. All variables are scaled from 0 to 1.

 

6. OUTPUT OF HGM MODEL

a. Project wetland functional loss is estimated

b. Mitigation wetland gain is estimated

c. Loss of function in the impacted wetland must be offset by an adequate acreage of increased function in the restoration site.

 

HGM: Using the Functional Assessment Guidelines

1. The accounting matrix: Function Loss vs. Function Created (Damage/Mitigation) (Project/Restoration Wetland Index)

2. Use of reference wetlands

a) Establishes highest function that may be expected (Reference Standard Wetlands) in

- a similar kind of wetland

- in the same watershed

b) Takes into account

- seasonal differences

-natural variation

- climatic cycles

c) Should pick up changes due to impacts

3. The function with the biggest ratio of function lost to function established is the one that controls (the one that requires the most acreage in return for acres damaged).

4. 1999 "Methods for Assessing Wetland Functions: Riverine and Depressional Wetlands in the Lowlands of Western Washington"

a) Focus is on Riverine and Depressional Wetlands

b) There is overlap (riverine) , (depressional)

-depressional outflow

-depressional closed

-riverine impounding

-riverine flow-through

5. Functions are placed in three categories

Water Quality Improvement

Potential for removing sediment

Potential for removing nutrients

Potential for removing heavy metals and toxic organics

Hydrology

Potential for reducing peak flows

Potential for decreasing downstream erosion

Potential for recharging groundwater

Habitat Suitability

General habitat

Invertebrate habitat

Amphibian habitat

Anadromous fish habitat

Resident fish habitat

Wetland-associated bird habitat

Wetland-associatesd mammal habitat

Native plant richness

Potential for primary production and organic export

6. Example of assessment of a function

a) A function (such as sediment removal) is represented by a score that combines several variables (V).

b) Variables represent measurable environmental characteristics (D - values or Data values) that are considered important in the performance of a function.

c) Function scores are calculated for

-effectiveness

-reduced performance

7. Water quality category, "Sediment Removal" example

a) Calculation page for "Depressional Outflow Wetlands - Function: Removing Sediment"

b) "Model at a Glance"

Variables (V storage, etc.)

-description

-what is measured

- rationale

c) D - (Data) values