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Third Generation Plan



The Shingle Creek and West Mississippi Watershed Management Commissions have adopted a new Third Generation Watershed Management Plan guiding the years 2013-2022. This plan was approved by the Minnesota Board of Water and Soil Resources on March 27, 2013 and adopted by the two Commissions on April 11, 2013. The Third Generation Watershed Management Plan is the culmination of an almost two-year planning effort by the two Watershed Management Commissions, the cities that are members of these Joint Powers Organizations, state agencies, and the public. The Plan sets forth goals and strategies that will guide water resources management activities in the two watersheds over the coming decade. The goals and strategies can be reviewed below.

Commission Amends Management Plan to Adopt Atlas 14 Precipitation Frequency Standards

On July 11, 2013, the Shingle Creek and West Mississippi Watershed Management Commissions approved an amendment to their joint Third Generation Watershed Management Plan that adopted a revision to Appendix C of their Rules and Standards.  Effective July 12, 2013, the revision adopted the new National Oceanic and Atmospheric Administration (NOAA) Atlas 14 precipitation frequency standards, replacing the outdated Weather Bureau Technical Paper 40 (TP-40) standards. These standards are used in hydrologic and hydraulic modeling to estimate stormwater runoff. The Atlas 14 standards were developed using a much longer period of record and larger data set than TP-40 and are more accurate. With TP-40 a single value represents, for example, a 100-year (1 percent chance), 24 hour rain event for an entire watershed. An online tool is available at http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=mn to determine critical event rainfall depths for an individual location.

Mandatory use of the Atlas 14 precipitation depths is waived for projects that are at greater than 30 percent design as of the date of adoption of the amendment, July 11, 2013.

The amendment revises Appendix C, Rules and Standards, Rule D.3.(b), shown below as additions (underlines) or deletions (strike outs).

 

(b)   Runoff rates for the proposed activity shall not exceed existing runoff rates for the 2-year, 10-year, and 100-year critical storm events for the project location as set forth in NOAA Atlas 14 Volume 8, published June 2013, or its successor, using the online NOAA Precipitation Frequency Data Server or a similar data source. Applicant must document the location and event depths used. The storm event table is shown below. If an approved local water management plan requires more restrictive rate control, then the more restrictive rate shall govern. Runoff rates may be restricted to less than the existing rates when necessary for the public health and general welfare of the watershed. Member cities and project review applicants shall not exceed discharge rates at City boundaries as determined in the Commission's hydrologic model.

Table 2.3. Storm event depths by return frequency.

Return  Frequency

24-hour

12-hour

6-hour

3-hour

2-hour

1-hour

30-min

15-min

2-year

2.8

2.4

2.1

1.7

1.7

1.4

1.1

0.7

10-year

4.2

3.7

3.1

2.6

2.5

2.1

1.7

1.3

100-year

5.9

5.0

4.4

3.8

3.5

2.9

2.4

1.7

Source:  US Department of Commerce, Weather Bureau, Technical Paper No. 40 (TP-40).



THIRD GENERATION PLAN  


Overview

Third Generation Plan

Appendix A
Appendix B
Appendix C - Amended
Appendix D
Appendix E
Appendix F
Appendix G


If you have any questions, please direct them to the Commissions' consultant:

 

Diane Spector

Wenck Associates

dspector@wenck.com

763.479.4280