Memorandum

City of Lawrence

Public Works

TO:	Dave Corliss, Debbie Van Saun, Charles Soules, Sheila Stogsdill, Dena Mezger
FROM:	Matt Bond
Date:	April 20, 2007
RE:	North Lawrence Drainage Study - Recommendations

After reviewing the North Lawrence Drainage Study (NLDS) the following overview outlines both short and long term recommendations with regards to current flooding and future development in North Lawrence.  The NLDS has provided a list of recommended improvements totaling $41 million.  While it currently is not fiscally possible nor is it prudent to finance all of these recommended improvements, the NLDS provides a baseline from which to start.  The executive summary of the NLDS lists the following four major recommendations which directly affect future development in North Lawrence. 

Ø “Drainage from north of 24/40 Highway should be cutoff by the highway embankment and the water should be pumped over the levee at a point just east of the 24/40 intersection to reduce the burden on the 2^nd Street Pump Station.”

Ø “Future developments in the watershed should maintain the current conveyance levels in the 100-yr floodplain – development should not reduce the capacity for floodplain storage.”

Ø “The City should purchase parcels of land as necessary for use as dedicated ponding area.”

Ø “Major roads and hydraulic structures should be improved to meet the current APWA criteria with regard to overtopping during the 100-year event, in order to provide adequate emergency services to the area.”

Relative to the first point, raising the 24/40 highway embankment west of US-59 would cut off the flow of water into the City from the north but at an estimated project cost of $24,802,000.  It would be reasonable to let the development of the property north of 24/40 Highway dictate when this will take place and at least share in the cost.  This same reasoning can be applied to upgrading of 2^nd Street Pump Station and its downstream piping. 

Staff concurs with the second recommendation regarding floodplain conveyance but takes exception to a related statement.  The executive summary of the NLDS, states “Due to the extensive hydraulic studies detailed in this report, it would not be necessary for developers to conduct individual studies, as long as the general recommendations of this study are followed (i.e. conveyance needs to be maintained with the floodplain).” Until recommended “Internal Systems” can be completed and are operational it is recommended that a Hydrologic & Hydraulic (H&H) Study continue to be a requirement for any future development located within the floodplain in North Lawrence.  Additional development within the floodplain has the potential to raise the overall water surface elevation for surrounding properties resulting in property damage.  The continued requirement of an H&H study will help to identify these situations.  For areas outside the floodplain the report can serve as the H&H study on a site specific basis provided that current conveyance levels are maintained and that there is no net reduction in overall floodplain storage.

The third recommendation from the NLDS was the acquisition of land to pond stormwater.  It is recommended that as opportunities for property acquisition present themselves that the City evaluate potential benefits for stormwater detention.

Total compliance with the fourth and final recommendation of improving major roads and hydraulic structures to meet the current APWA criteria will not be possible until construction of or improvements to pump stations north of 24/40, at 6^th & Maple and on 2^nd Street are complete.

The NLDS identifies twelve separate internal drainage systems.  It is recommended that the next stormwater capital improvement project that the City finances should be the implementation of the System 6 improvements.  It should be noted that System 4 improvements are currently in the design phase.

Ø System 4 - 2^nd & Locust

     This intersection is scheduled for an October 2007 bid date.  The original project scope included only geometric improvements. Since then the NLDS recommended improvements have been included in the design of this project.  The railroad underpass on North 2^nd Street in its current state fills with water and becomes impassible during significant rain events.  While the implementation of all of the System 4 improvements will not keep this under pass clear during every rain event, it will open it quicker after the heaviest of rains and enable it to remain open during smaller rain events that currently render it impassable.  The intersection reconstruction offers an opportunity to provide storm sewer upgrades while the street is already under construction.  Inclusion of the storm sewer improvements also demonstrates to the public long range planning with regards to infrastructure.

Ø System 6 - Maple Street Pump Station (529 Maple)

          This system provides the biggest benefit relative to area affected.  Storm water runoff in central North Lawrence currently has no drainage relief path.  This is due to the topography of the area, primarily because of the railroad tracks on the south.  (It should be noted that this area is currently designated by FEMA as floodplain and will remain so even with the completion of the system improvements.)  This system will more than likely have to be broken up into phases given its estimated total cost      of $4,375,000 with the pump station construction comprising $3,204,000     of that projected cost.

An important fact to remember during any system upgrade: “improvements are to generally be made in a downstream to upstream manner within the system, as there is no advantage trying to deliver more flow to a downstream component that cannot convey the existing flow.”

In summary, staff recommends that development of the property north of 24/40 Highway dictate when NLDS recommendations take place and that developers at least share in the cost.  H&H studies will continue to be required for proposed future developments in the floodplain. For areas outside the floodplain the report can serve as the H&H study on a site specific basis provided that current conveyance levels are maintained and that there is no net reduction in overall floodplain storage.  The next major capital improvement project that the City finances should be the implementation of the system 6 improvements which include a new pump station at 529 Maple and its corresponding piping.  It is also recommended that the property on the SE corner of 7^th & Maple be acquired to provide a dedicated ponding and bio-retention area.  These projects in conjunction with the 2^nd & Locust project, currently in the design phase, will provide meaningful benefits in North Lawrence and will allow us to address stormwater issues in other areas of the community as well.