7.
City Council Work Session
- Meeting Date:
- 05/10/2016
- From:
- Chris Kirkendall, Stormwater Manager
- Department:
- Utilities
Co-Submitter:
TITLE:
Presentation on Flooding and Low Impact Development In Flagstaff
DESIRED OUTCOME:
Information only
EXECUTIVE SUMMARY:
In 2015, a Future Agenda Item Request was brought forward by Councilmember Oravits to have staff provide a presentation on Low Impact Development in Flagstaff, and majority of Council agreed to move this item forward. The second (Layout) and third (Detail) attachments have been provided at the request of Councilmember Oravits.
The Stormwater Section at the City of Flagstaff is tasked with implementation of multiple programs related to stormwater. One of the major responsibilities is to provide support to the City’s Development Engineering Section through the permitting review process which is where the LID (Low Impact Development) program is implemented. This Staff Summary will provide an overview of the Stormwater program focusing on Low Impact Development.
The Stormwater Section at the City of Flagstaff is tasked with implementation of multiple programs related to stormwater. One of the major responsibilities is to provide support to the City’s Development Engineering Section through the permitting review process which is where the LID (Low Impact Development) program is implemented. This Staff Summary will provide an overview of the Stormwater program focusing on Low Impact Development.
INFORMATION:
LID implementation was phased in over several years beginning in February of 2009 as a voluntary program. In March of 2010 the one half inch retention requirement was implemented. In March of 2011 the one inch of retention requirement was made mandatory for development within the City.
Development increases runoff by removing vegetation and installing impervious surfaces. This work increases the stormwater volume and pollution from a site. LID is a form of retention that holds stormwater volume onsite resulting in a reduction to volumetric flooding. LID also provides a water quality benefit through filtration and reduced erosion.
Volumetric flooding is caused by existing infrastructure’s inability to pass a given storm volume, which results in a backup or lake. It is like a slow drain or bath tub that is backed up. LID directly reduces this type of flooding by holding stormwater volume onsite. This volume either infiltrated back into the groundwater table or is slowly released over a long period of time. LID delays the costly replacement of undersized downstream infrastructure by reducing damage caused by flooding.
LID reduces erosion and provides filtration of runoff which reduces nonpoint pollution. Runoff entering LID systems is filtered through vegetation and bio-retention soils removing pollutants from the water. This water quality benefit supports the goals of the City’s MS4 permit.
New development is currently required to retain one inch of runoff from new impervious surfaces onsite and release this volume in 24 to 36 hours. Detention of the two-year storm is waived with implementation of LID retention.
Without LID volumetric flooding in areas like Southside and Continental will continue to increase. Maintenance cost to the public to replace undersized infrastructure in flooded areas will continue to increase. Further nonpoint pollution and erosion will increase from developed sites. Basically LID retention provided a mechanism for grows to mitigate impacts from growth.
COUNCIL GOALS:
3) Provide sustainable and equitable public facilities, services, and infrastructure systems in an efficient and effective manner to serve all population areas and demographics
4) Develop and implement guiding principles that address public safety service levels through appropriate staff levels
6) Provide a well-managed transportation system
7) Continue to implement the Flagstaff Regional Plan and focus efforts on specific plans
9) Improve the economic quality of life for Flagstaff through economic diversification, and by fostering jobs and programs that grow wages and revenues
11) Ensure that we are as prepared as possible for extreme weather events
REGIONAL PLAN:
Development increases runoff by removing vegetation and installing impervious surfaces. This work increases the stormwater volume and pollution from a site. LID is a form of retention that holds stormwater volume onsite resulting in a reduction to volumetric flooding. LID also provides a water quality benefit through filtration and reduced erosion.
Volumetric flooding is caused by existing infrastructure’s inability to pass a given storm volume, which results in a backup or lake. It is like a slow drain or bath tub that is backed up. LID directly reduces this type of flooding by holding stormwater volume onsite. This volume either infiltrated back into the groundwater table or is slowly released over a long period of time. LID delays the costly replacement of undersized downstream infrastructure by reducing damage caused by flooding.
LID reduces erosion and provides filtration of runoff which reduces nonpoint pollution. Runoff entering LID systems is filtered through vegetation and bio-retention soils removing pollutants from the water. This water quality benefit supports the goals of the City’s MS4 permit.
New development is currently required to retain one inch of runoff from new impervious surfaces onsite and release this volume in 24 to 36 hours. Detention of the two-year storm is waived with implementation of LID retention.
Without LID volumetric flooding in areas like Southside and Continental will continue to increase. Maintenance cost to the public to replace undersized infrastructure in flooded areas will continue to increase. Further nonpoint pollution and erosion will increase from developed sites. Basically LID retention provided a mechanism for grows to mitigate impacts from growth.
COUNCIL GOALS:
3) Provide sustainable and equitable public facilities, services, and infrastructure systems in an efficient and effective manner to serve all population areas and demographics
4) Develop and implement guiding principles that address public safety service levels through appropriate staff levels
6) Provide a well-managed transportation system
7) Continue to implement the Flagstaff Regional Plan and focus efforts on specific plans
9) Improve the economic quality of life for Flagstaff through economic diversification, and by fostering jobs and programs that grow wages and revenues
11) Ensure that we are as prepared as possible for extreme weather events
REGIONAL PLAN:
?Policy WR.5.7. Support healthy watershed characteristics through implementation of practices, consistent with the City of Flagstaff Low Impact Design Manual, that improve flood control and flood attenuation, stormwater quality, and water sustainability; increase groundwater recharge; enhance open space quality; increase biodiversity; and reduce land disturbance and soil compaction.