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Stormwater Management Development Standards

Stormwater Management Development Standards

As part of the review of any site plan, preliminary plat or construction drawings for development within the City of Johnston, a detailed stormwater management plan is required, pursuant to the regulations within Chapter 145 of the Johnston Municipal Code. 

Stormwater Calculations

Chapter 145.09.2(C) details the specific requirements for stormwater calculations and standards.  Designers of stormwater management practices are encouraged to review the Technical Guidance document which was prepared as part of the Watershed Assessment and Stormwater Management Plan.  Specifically, Page 122 contains a checklist for stormwater calculation reports and Page 123 provides a Data Sheet that should be included with the submission of any Stormwater Management Report.  Designers should also reference the Iowa Stormwater Management Manual, as this has been adopted as the design standard for any stormwater management facility constructed with the City of Johnston.

Questions pertaining to the preparation of stormwater calculations and stormwater management plans can be directed to Foth Infrastructure and Environment, the City’s Consulting Engineer.

Grading Permits and Erosion Control Monitoring and Inspections

Chapter 145.06 requires a Grading Permit to be issued prior to any ground disturbing activity.  If the ground disturbing activity is larger than one acre in size, an NPDES General Permit # 2 from the Iowa Department of Natural Resources is also required, with information available from the Iowa DNR.

For sites with a ground-disturbing activity over one acre, a city-issued grading permit is required to be submitted with a Stormwater Pollution Prevention Plan (SWPPP), a checklist of required information to be included on the SWPPP is available here.   For sites with ground-disturbing activity under one acre, the grading permit form is also required along with a Stormwater Runoff Control Plan.  A grading permit is also required with the issuance of every building permit.

Chapter 145.20 and 145.23, as well as the requirements of the Iowa DNR NPDES General Permit # 2, require holders of a Grading Permit to conduct regular inspections of their site to ensure compliance with all City, State and Federal Regulations and take any corrective actions necessary to remain in compliance. 

Questions pertaining to Grading Permits or Erosion Control Inspections can be directed to Eric Rehm, Building Inspector II.  He can be reached at 515.727.7779.

Stormwater Management Maintenance Agreements

Any permanent stormwater management practice installed on a property requires routine maintenance.  As such, a Stormwater Management Maintenance Agreement is required to be executed by the property owner and recorded with the Polk County Recorder’s Office for any required stormwater management practice.  A template agreement is available here.  Please note the template is very generic and the maintenance requirements should be determined by the design engineer based upon the requirements of the designed practice.

Questions pertaining to Stormwater Management Maintenance Agreements can be directed to David Wilwerding, AICP, Community Development Director.  He can be reached at 515.727.7775 or through Dave's E-mail.

Stream Buffers
As part of any platting action a stream buffer shall be provided according to the stream type on the property. Use the following map to find the classification of any stream on the property.