Monday, June 20, 2016

How to reduce flooding


 Sustainable Stormwater Solutions for Sedona and Village of Oak Creek


Sedona was asking for input on their stormwater management plan to reduce Monsoon flooding. So we put forth these recommendations: let Nature do a lot of the work.

The Goal: Managing for Multiple Benefits

Elegant, sustainable solutions to stormwater and flooding should address social, economic and environmental needs.
PEOPLE
PROSPERITY
PLANET
Reduce inconvenience and stress associated with flooding (eg, road blockages, fear of property damage).
Eliminate potential for loss of life.
Reduce stormwater flowing into the stormwater system which then must be treated and processed.
Reduce opportunity for property damage.
Reduce erosion and the spread of pollution
Maximize the use and retention of stormwater for landscapes and natural areas

Courtesy: Pima Association of Governments
Focusing on getting the rainwater quickly into the stormwater infrastructure is an ‘end of pipe’ approach. We believe that the Stormwater Management Plan should focus first on strategies that reduce stormwater from reaching the washes and slowing the water in the washes.  The following are recommendations from the Sustainability Alliance for a more sustainable, front-of-pipe solutions.

Reduce stormwater flows via “green infrastructure”


Hardscapes—Encourage property owners to manipulate the land to keep rainwater on their property, largely through ‘earthworks,’ manipulating the landscape drainage to retain water in a controlled fashion. This includes:
·       Porous pavement
·       Rainwater catchment systems for landscape irrigation
·       Rain gardens
·       Bioswales and collection ponds
·       Curb cuts that let water into natural areas like tree wells
·       Green roofs (not sure if these work in our harsh summers)


Softscapes and undeveloped land—City engineers should work with property owners along washes to:
·       Install check dams in the wash and use the silt as it builds up for landscaping
·       Remove debris and potential pollutants near and in the washes and culverts (and report large logs and debris to the City for removal before Monsoon Season)
·       Seed the banks with native plants to protect the washes from erosion




Investigate Public Policy Changes

Public policy has a large role to play in reducing stormwater flows and associated flooding.
·       Clarify ownership related to surface water. What can a property owner legally do and not do? (Is the table in the EPA document below still accurate?)
·       Where possible, create riparian buffers and/or buy up land adjacent to rivers to allow the rivers to flood naturally. Provide dry dams and ponds that can collect and slow stormwater. Avoid channelizing the water with barriers as this only moves the problem downstream.
·       Review building codes and urban plans for stormwater impacts. Do you require new construction to manage stormwater and use it in productive ways? Can you create incentives for HOA’s to put in stormwater collection systems? Have you zoned areas for development that should better be used as floodplains?

Resources we found especially useful
EPA—Green Infrastructure in Arid and Semi-Arid Climates: https://www3.epa.gov/npdes/pubs/arid_climates_casestudy.pdf
Lancaster, Brad—books on earthworks and rainwater harvesting: http://www.harvestingrainwater.com/

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