Jul 10, 2012 - Parts of Ward Rd and M150 flooded but passable. â¡ Radar images ... enter all homes through windows or d
MEADOWS AT SUMMIT RIDGE SW 33RD ST. FLOODING Residents’ Meeting July 10, 2012
Background
SW 33rd St. and associated infrastructure in Meadows at Summit Ridge constructed in two phases end (east of Windsong) with 4th plat – 2004 West end (between Ward & Windsong) with 5th plat – 2005 East
Building permits issued between 2005 and 2008 Addresses
616 & 704 in 2005 Addresses 612, 700, 924 & 928 in 2006 Address 620 in 2008
2001 Aerial Photo
City Regulations
At time area was platted applicable standards were the 1992 City of Lee’s Summit Design & Construction Manual Storm sewer system design based on future upstream land use Level of service required for storm drainage system was the 1% (“100-year”) storm
Pipe system required to handle flows from 10% (“10-year”) storm
7.92” in 24 hours with peak hour of 3.58 “
5.2” in 24 hours with peak hour of 2.39”
1% storm to be handled either routed through surface channels around structures or by same pipe system with added capacity
Existing System Design
Designed assuming future residential development upstream Plans indicate1% storm to be handled in pipe system System designed with area inlets near pipe entrances to accommodate overflows System designed to allow headwater building up at system entrances to “push” water into pipes and inlets Standard practice, allowable design Because of limited space between system entrance and homes, some ponding occurs in residents’ yards
May 25, 2012
Seven homes on SW 33rd reported water in basements 612, 616, 620, 700, 704 near east storm sewer entrance 924, 928 near west storm sewer entrance
M291 & Hook Road flooded – MoDOT closed M291 Parts of Ward Rd and M150 flooded but passable Radar images show heaviest storm activity in a narrow band generally along M150 TV news reported 5” of rain fell in 1 hour
Evaluation/Analysis
City engineering staff gathered extensive amounts of information regarding the system performance and conditions that existed in area at the time of storm Amount and intensity of rain which exceeded level of service required for drainage systems identified as primary cause of flooding 5”
rainfall exceeded peak hour of standard 1% design storm
Sources of Flooding
Measured high water marks indicate water apparently did not enter all homes through windows or doors - overwhelmed foundation drains & sump pumps caused flooded basements House No. – all on SW 33rd Street
Surveyed Low Opening Elevation at Window/Door Sill
Surveyed Ground Elev. At Back of House
Surveyed High Water Elevation
Minimum Low Opening Elevation Req’d by Plat
612
1010.97 (window)
Not Avail.
1009.95
N/A
616
1010.59 (door)
1009.04
1009.95
1009.8
620
1005.94 (window)
Not Avail.
1009.95
1009.8
700
1009.02 (window)
1008.40
1009.95
1009.8
704
1009.99 (window)
1008.79
1009.95
N/A
924
997.42 (window)
995.38
996.26
998.6
928
997.33 (window)
996.28
996.26
998.6
Fence on east side of 620 High water mark visible on fence measured as 1009.95
Back patio & basement windows at 924 Orange string line shows high water elevation measured as 996.26
Other Contributing Factors
During field investigation staff found a number of conditions that contributed to flooding All factors converged during this one storm event None of additional factors individually were reason for flooding Flooding
would have occurred even without contributing
factors Made results worse than might otherwise have occurred
Upstream Surface Conditions
Farm ground immediately upstream from SW 33rd St. was almost bare earth after vegetation had been cut Rain
over night May 24-25 saturated surface to some degree Rate of runoff from saturated, un-vegetated area as much as 50% higher than area with crop vegetation, turf or some other plant ground cover
Ag fields approximately 2 weeks after storm On May 25 fields looked like area in foreground
Obstruction of West Area Inlet
Area inlet behind 924 SW 33rd has no openings for water to enter Original
design was inlet with 6-inch tall openings on all four sides Construction contractor installed a solid box with no openings, removing all overflow capacity provided at this location
Constriction at West Pipe Entrance
Block retaining wall, fill and fence placed for yard at 920 constricts area previously available for headwater to pond Wall
and fill not included in original grading & drainage plan Deflects water to the west Fence blocks intended drainage swale from east and may trap water inside the back yard of 920
System entrance behind 924 Orange string is high water based on mark on fence
Obstruction of East Area Inlet
Fence constructed over and around east half of area inlet located on property line between 616 & 620 SW 33rd Blocked water from reaching inlet until enough ponding occurred to push water under and through fence Marks on fences show water built up higher around half of inlet on 620 side than inside fence on 616 side
East area inlet Fence surrounds half of inlet
Fences Across Drainage Swales
Original grading plan for development shows drainage swale on common tract behind homes on SW 33rd and along back lot lines to carry runoff to storm sewer entrances Fences on several lots extend outside of individual lots and across common tract, obstructing swale, backing water up on some properties
Fences across common tract Contours show drainage pattern obstructed by fences
Fences across common tract 900 block
Storm Sewer System Design
City engineering staff identified questions about the original design and construction of the east system Discrepancy
in size of upstream drainage area between City information and original plans Capacity of area inlets may be slightly overestimated
Information has been requested from original design firm to resolve questions
What Can Be Done for Future
Immediate steps - remove obstructions in the drainage system (obstructing drainage ways is violation of City ordinance) Install
openings in west area inlet (City) Remove fence around east area inlet (resident) Make sure fences allow water to flow in swales (residents) Raise
portion of fence to allow flow beneath Move or remove portions of fence
Additional Possibilities for Residents
Yard re-grading may help keep water farther away from some homes City
staff can offer some advice
Investigate additional sump pump capacity (larger pumps) and back up power source Discuss flood insurance with your insurance agent As
a participating community in the National Flood Insurance Program all homes in Lee’s Summit are eligible for flood insurance
Summary
Rainfall amount and intensity of May 25, 2012 storm exceeded standard design conditions A number of other factors contributed to flooding but did not cause it Existing drainage system was designed to provide the required level of service (1% storm event) in accordance with City standards Unless the existing drainage system is identified as being deficient – not providing the required level of service – improvements to the public infrastructure are not indicated
