Laserfiche WebLink
June 1, 2007 <br /> Page 2 <br /> recurrence interval be followed for this Soo acre drainage basin. Based on the <br /> magnitude of a storm that could be expected once every ioo years, a peak flow of iSoo <br /> cfs was calculated. This flow required that a trapezoidal, earth-lined drain channel be <br /> constructed that was zS' wide (at the bottom) at an average depth of 8'. This drain <br /> channel was two miles long and terminated in one three acre and two twenty acre <br /> retention basins. <br /> This drainage improvement cost $4.S million. Its cost is spread over the expected 730 <br /> residential units within this project. The allocated cost per unit is $6,200. In other <br /> words, each unit within this development is "charged with" this amount to address <br /> offsite drainage infrastructure. Remember, this is in an area that receives about 30" rain <br /> per year! Also, the ground slope in this area is only about i% - 2%, with deep soil ground <br /> conditions. So, the land characteristics are very conducive to an economic and cost <br /> effective drainage design. In its 12 years of existence, water flow in the drain channel has <br /> never exceeded 3" in depth (for an 8' deep channel) and water has never reached either <br /> of the two 20 acre retention basins. I have attached a few photos, to show you what this <br /> drain channel and retention basins look like. <br /> In addition, the requirement to address the ioo-year storm has been expanded beyond <br /> the modification of FEMA designated flood zones and is proposed to also apply to the <br /> alteration of any water course. This is impractical and unnecessary. <br /> Can you imagine what impacts these proposed requirements would have on the planned <br /> <br /> Waikoloa Workforce/Unidev Housing project in Waikoloa? That drainage basin is <br /> probably 20,000 to 30,000 acres, as it starts at the summit of Mauna Kea and fans in the <br /> <br /> Westerly direction towards Waikoloa Village. The cost to contain all rainfall from a ioo- <br /> year storm would be astronomic! These units would not be able to be constructed and <br /> sold in the affordable category. <br /> We ask that you and your colleagues on the Council defer action at this time, work with <br /> the Department of Public Works and revise Bill Sl back to its original intent and content. <br /> Sincerely, <br /> Riley W. Smith, P.E. (#4959) <br /> <br /> Vice President <br /> Land & Asset Management <br /> <br /> Attachments: Photos <br /> 67-1435 Ivlamalahoa liwy., Kamucla, I-[awaii 96743 <br /> Tel.:(808)885-7311 • Fax:(808)88~-5602 ~ wvvw.parkerranch.com <br /> <br />