Title
Consider/Discuss/Act on a Request for a Variance to the Detention Requirements of the Stormwater Management Ordinance for the Oak Hollow Office Park Development
Summary
MEETING DATE: August 20, 2013
DEPARTMENT: Engineering
CONTACT: W. Kyle Odom, CFM, RS, Environmental Engineering Manager
Daniel Still, PE, CFM, Civil Engineer
RECOMMENDED CITY COUNCIL ACTION:
* City staff recommends approval the variance request regarding the 10-year storm.
* City staff recommends denial of the request regarding the 1-year storm.
ITEM SUMMARY:
* The developer of the Oak Hollow Office Park has requested that the City Council grant a variance to the detention requirements of the Stormwater Management Ordinance.
BACKGROUND INFORMATION:
* In 2006, the City Council directed City staff to amend the Stormwater Management Ordinance to address erosion in McKinney's creeks and streams. The 2006 amendments include the following:
o Runoff from the 1-year, 24-hour storm shall be detained and released in not less than 12 hours.
o The post-development 10-year peak discharges shall not exceed the pre-development 10-year peak discharges.
o If a developer elects not to detain as indicated above, then the channel stability of the impacted stream must be evaluated downstream to the nearest major receiving stream and, if necessary, channel stabilization measures must be constructed or financially guaranteed.
o Also, detention of storms larger than the 10-year storm (i.e. the 100-year storm) are not advisable nor required if it is determined that such detention would create a coincidental peak (create an increase in the creek's flow rate for the design storm).
* The developer's consultant provided a drainage study of the creek upstream of SH 5 demonstrating that:
o On-site detention will slightly increase the stream 100-year peak flow at SH 5 due to coincidental peaks.
o On-site detention will also slightly increase the stream 10-year peak flow at SH 5 due to...
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