Calculating Credits and Debits for Compensatory Mitigation in - - PowerPoint PPT Presentation

Calculating Credits and Debits for Compensatory Mitigation in Wetlands of Western Washington

Patricia Johnson Washington State Department of Ecology

Debits and Credits

Debits = area-based units representing the loss

• f wetland functions

at an impact site Credits = area-based units representing the gain of wetland functions at a mitigation site

Background

• Creates functional currency to compare

functions and values lost to those proposed

• Based on the Washington State Wetland

Rating System for Western Washington

• HGM based

Function Groups

Improving water quality – Water Quality Flood storage and flow reductions – Hydrologic Habitat for plants and animals – Habitat

Photo courtesy of King County, WA

Score for each function based on a qualitative rating of:

• The potential of the site to provide the function
• The potential of the landscape to maintain each

function at the site scale

• The values each function may have for society

What is the potential of the site to provide the function?

Based on indicators of structure.

Site Potential:

What is the potential of the landscape to affect the function at the site scale?

Landscape Potential:

What is the value of the function to society?

Value:

Scoring for each function

Site potential + Landscape potential + Value High = 3 Medium = 2 Low = 1 H,H,H = 9 H,H,M = 8 H,H,L = 7 H,M,M = 7 M,M,M = 6 H,M,L = 6 H,L,L = 5 M,M,L = 5 M,L,L = 4 L,L,L = 3

Example Wetland Impact (Debit):

Before After

Example Wetland Impact (Debits)

Rating of Wetland Unit BEFORE impact

Function Improving Water Quality Hydrologic Habitat Site Potential (H, M, L) M = 2 L L Landscape Potential (H, M, L) H = 3 H M Value (H, M, L) L = 1 L L Score for Wetland Unit 2 + 3 + 1 = 6 5 4

Losses (Debits) and Gains (Credits) are estimated by multiplying the score by the area and by the appropriate Modifier

Photo courtesy of King County, WA

Calculating Debits

Modifier: Temporal Loss Factor

Calculating Debits

Score (Water Q.) x Area x TLF = Debits (Water Q.) Score (Hydrologic) x Area x TLF = Debits (Hydrologic) Score (Habitat) x Area x TLF = Debits (Habitat)

Example: DEBITS from Impact

DELAYED Mitigation

Improving Water Quality Hydrologic Habitat Score for Wetland Unit

6 5 4

Acres of impact

(non-forested)

1

Basic mitigation requirement (BMR)

6 x 1 = 6 5 4

Temporal loss factor (Delayed)

3

DEBITS

6 x 3 = 18 15 12

Total Debits: 18 + 15 + 12 = 45 Permittee purchases 45 credits from ILF Program

Calculating Credits

Basic Credits = Increase in Score

[Score at “maturity” of site – Score before] Creation : Score before = 0 Re-establishment: Score before = 0 Rehabilitation: Score before = (from form) Enhancement: Score before = (from form)

Example ILF Mitigation Site (Credits)

Before After

Example ILF Mitigation Site (Credits)

Rating of Unit BEFORE mitigation

Improving Water Quality Hydrologic Habitat Site Potential (H, M, L) M = 2 M M Landscape Potential (H, M, L) H = 3 H L Value (H, M, L) H = 3 H H

Score 2 + 3 + 3 = 8 8 6

Improving Water Quality Hydrologic Habitat Site Potential (H,M,L) H = 3 H H Landscape Potential (H,M,L) H = 3 H L Value (H,M,L) H = 3 H H

Score 3 + 3 + 3 = 9 9 7

Example ILF Mitigation Site (Credits)

Rating of Unit AFTER mitigation

Calculating Credits

Modifier: Risk of Failure

Type of Mitigation Risk Factor Advance mitigation The site meets criteria in Charts 1 and 3 of the site selection guidance [i.e. identified in a local plan and is sustainable] AND meets the criteria in Charts 4- 11 for the appropriate functions. (Ecology publication #09-06-032)

Advance means that at least two years has passed since plantings were completed or one year since “as-built” plans were submitted to regulatory agencies.

1.0 Advance mitigation without meeting criteria in Ecology publication #09-06-032 0.83 Concurrent Mitigation Mitigation site meets criteria in Charts 1 and 3 of the site selection guidance [i.e. identified in a local plan and is sustainable] AND meets the criteria in Charts 4-11 for the appropriate functions. (All worksheets for Chart 3 and in Appendix D of Ecology publication #09-06-032 are submitted) Risk factor applies to all types of mitigation. 0.9 Mitigation site chosen meets the criteria in Charts 2 and 3 of the site selection guidance [i.e. identified as a site with potential and that is sustainable] ; AND meets criteria in Charts 4-11 for the appropriate functions. (All worksheets for Chart 3 and in Appendix D of Ecology publication #09-06-032 are submitted) Risk factor applies to all types of mitigation. 0.80 Site does not meet criteria in site selection guide, or guide was not used. Re-establishment, rehabilitation, or enhancement of an aquatic bed, shrub, or forest community Re-establishment, rehabilitation, or enhancement of an emergent community Creation of an aquatic bed, shrub, or forest community with data showing there is adequate water to maintain wetland conditions 5 years out of every 10. Creation of an emergent community with data showing there is adequate water to maintain wetland conditions 5 years out of every 10. Creation of an aquatic bed, shrub, or forest community without adequate hydrologic data. Creation of an emergent community without adequate hydrologic data. 0.67 0.5 0.67 0.5 0.5 0.4

Calculating Credits

Increase in Water Q. Score x Area x RF = Credits (Water Q.) Increase in Hydrologic Score x Area x RF = Credits (Hydrologic) Increase in Habitat Score x Area x RF = Credits (Habitat)

Improving Water Quality Hydrologic Habitat Rating of Unit AFTER mitigation 9 9 7 Rating BEFORE mitigation Increase in Score (A-B) 9 - 0 = 9 9 7 Acres CREATED 1 Basic mitigation Credit 9 x 1 = 9 9 7 Risk Factor 0.9

CREDITS 9 x 0.9 = 8.1 8.1 6.3

Example ILF Mitigation Site (Credits)

Proposed Credits for CREATED Wetland Areas

Example ILF Mitigation Site (Credits)

Proposed Credits for Enhanced Wetland Areas

Improving Water Quality Hydrologic Habitat Rating AFTER mitigation 9 9 7 Rating BEFORE mitigation 8 8 6 Increase in Score (A-B) 9 – 8 = 1 1 1 Acres ENHANCED 12 Basic mitigation Credit 1 x 12 = 12 12 12 Risk Factor 0.9

CREDITS 12 x 0.9 = 10.8 10.8 10.8

Improving Water Quality Hydrologic Habitat CREATED Credits 8.1 8.1 6.3 ENHANCED Credits 10.8 10.8 10.8 TOTAL CREDITS 8.1 + 10.8 = 18.9 18.9 17.1

PROPOSED Total Credits for the Project = 54.9

Example ILF Mitigation Site (Credits)

Proposed TOTAL Credits

Total Credits: 18.9 + 18.9 + 17.1 = 54.9

Comparing Debits to Credits

• Wetland Impact Debits with Delayed TLF:

45 total Debits

 18 debits for Water Quality  15 debits for Hydrologic  12 debits for Habitat

• PROPOSED Credits for ILF Mitigation Site:

54.9 total Credits

 18.9 credits for Water Quality  18.9 credits for Hydrologic  17.1 credits for Habitat

An ILF mitigation site must fulfill at least as many credits (released) as the number sold to permittees (debits).

Photo courtesy of King County, WA

Credit – Debit Tool is Guidance

• SCORES from the Tool provide a STARTING POINT
• Tool may not capture site-specific factors on debit
• r credit end
• Do not want Tool to drive the design

Questions?

31

Patricia Johnson WA Dept. of Ecology (360) 407-6140

Patricia.johnson@ecy.wa.gov http://www.ecy.wa.gov/programs/sea/wetlands/mitigation/creditdebit/index.html