Memorandum

City of Lawrence

Public Works

 

TO:

Dave Corliss

FROM:

Matt Bond, P.E. - City Stormwater Engineer

Date:

January 11, 2008

RE:

Chad Voigt letter – Airport Business Park

 

The following letter was received from a Lawrence resident.  It was written by the former City Stormwater Engineer Chad Voigt concerning the proposed Airport Business Park, North Lawrence development in general and the North Lawrence Drainage Study.  Although staff does not disagree with the technical analysis provided by Mr. Voigt, the letter expresses opinions regarding several policy issues.  City staff has not addressed the opinions expressed but has tried to provide information to clarify points of concern mentioned in the letter.  Staff recognizes the unique characteristics of the watershed and how the corresponding stormwater drainage affects North Lawrence.  After each point expressed in the letter is an expansion and clarification relating to the referenced topic.  Excerpts from Mr. Voigt's letter are in italics.

 

November 18, 2007

To: Bob Lominska

From: Chad Voigt

 

Bob,

 

These are my thoughts on the proposed Airport Business Park, and North Lawrence development in general. The North Lawrence Drainage Study identifies huge flood control projects that will be needed if the watershed develops as shown in conceptual land use plans.  Developers will not be able to pay for these projects, so the development potential of this land should be reevaluated. The City’s Comprehensive Plan should be updated to minimize the need for flood control projects. Land uses should be downgraded to minimize runoff, preserve soils and reduce public expense.

 

The Airport Business Park would be a leap toward the conditions forecast in the North Lawrence Drainage Study. If the development proceeds, these are the points that need more in-depth review and discussion:

 

Code Requirements

 

It seems there is a lack of understanding of the regulatory weight of the North Lawrence Drainage Study. All developments in the City are required (stormwater code and floodplain regulations) to provide studies and plans to prevent downstream stormwater impacts. For North Lawrence landowners, the scale of the floodplain and lack of viable management options mean that the required studies are beyond the resources of isolated developments.  The North Lawrence Drainage Study, paid for by the public, gives developers the technical material needed to complete a valid development proposal. Developers can use the North Lawrence drainage Study, or provide an equivalent independent study. Either way, each development is required by code to prevent downstream impacts.

 

The submittal for the Airport Business Park conforms to both the City’s Stormwater Management Criteria as well as current floodplain regulations.  It should be noted that only the northwest portion of the proposed development lies within the 100 year floodplain.  This area is being slated as an open tract and will not be developed.  This open tract as well as three other locations (see the attached map) will also be platted as floodplain overlay district.  The applicant for the Airport Business Park utilized the option of using the North Lawrence Drainage Study for the required Hydrologic & Hydraulic Study.  As the letter points out the drainage study was paid for by the public and provides not only a cost effective guideline for development but also provides a consistent guideline.  The entire watershed was modeled in the North Lawrence Drainage Study (NLDS).  Separate drainage studies by individual developments would not necessarily look at the effect on the entire watershed.

 

The North Lawrence Drainage Study identified $16.2 million in reconstruction projects that are needed to provide a minimal level of service to existing residents. At an average of $14,000 per acre, many of these projects will likely never be completed. (The City is still burdened with over $40 million in stormwater projects needed elsewhere, at a cost of roughly $6,000 per benefiting acre.)

 

The study also identified $24.8 million in flood control projects that will be needed if the watershed develops as shown in conceptual land use plans. With this in mind, it’s critical that new developments add to the solution rather than adding to the problem. New developments in North Lawrence should fully fund their internal drainage systems, as well as the additional projects needed to offset downstream impacts. Public funds should be directed at correcting existing drainage problems, and should not be directed at managing conditions created by new development.

 

The 1996 Stormwater Master Plan identified 41 projects that would reduce or eliminate flooding.  The 1996 plan split these projects into three groups with group one projects being the highest priority.  Of the eleven group one projects listed seven have been completed.  There are still approximately $40 million worth of potential uncompleted projects listed in the plan.  It should be noted that five of the projects listed in the 1996 Plan are in North Lawrence.

 

The Airport Business Park proposal references the North Lawrence Drainage Study; however I could not find any discussion of downstream impacts or proposed flood control measures.  In lieu of a discussion of actual impacts, the development should be expected to pay some share of the $24.8 million grand total. Based on a proportion of the undeveloped watershed area, this development would need to contribute $449,000. It appears that this amount would be lower if actual impacts are taken into account.

 

The Airport Business Park does in fact require $385,050 worth of improvements.  The development will require that two of the channel improvements listed in the NLDS be constructed.  These two channel improvements will increase the capacity of the Maple Grove drainage channel.   In addition to the channel improvements a cross road pipe under E. 1500 Road/ 7th Street will also be required.

 

Maple Grove Drainage

 

58 acres of the proposed business park currently drains to the Maple Grove drainage channel; which flows south to the City’s pump station on 2nd Street. This system is already overloaded, and additional runoff would increase flooding of surrounding properties. The business park development proposes to minimize this impact by diverting developed runoff east to the airport property. This will require significant fill along the west edge of the development, and construction of a drainage system to deliver flow to the east.

 

This intent should be clearly identified on the preliminary plat, including easements and proposed pipe layouts. The development should fully fund the drainage system needed within the platted area. The development should also fully fund the system needed to divert runoff to the east, to an acceptable point of discharge on the airport property. If there will be any discharge of developed runoff to the west, this should be specifically quantified so that impacts to the south can be determined and addressed by the developer.

 

Under existing conditions there are actually 105 acres that drain directly as well as indirectly to the Maple Grove drainage channel and then south to the pump station on 2nd Street.  Existing topography drains 58 acres of the proposed development directly into the Maple Grove drainage channel.  Present conditions also enable an additional 47 acres to drain south along the west side of E. 1500 Road/7th Street and eventually into the Maple Grove drainage channel.  The 47 acres of drainage that currently run south into North Lawrence will be rerouted through a pipe under E. 1500 Road and eastward into a slough that drains into Mud Creek.  The pipe along with channel improvements along the Maple Grove drainage channel will minimize the overall effects to the 2nd Street Pump Station.

 

Tributary A Impacts

 

Most of the proposed business park drains east to the airport, specifically to Tributary A which flows under Airport Road and East 1600 Road before flowing south under Highway 24/40 and Interstate 70. As with most North Lawrence drainage systems, Tributary A is very flat. Runoff from the business park development will increase the depth and duration of standing water adjacent to the airport runway. Further downstream, easements will eventually be needed where runoff increases standing water on existing farm land.

 

The North Lawrence Drainage Study identifies two bridge replacement needs on Tributary A, one at East 1600 Road and one at Highway 24/40. Flooding of East 1600 Road has been a concern in the past because it affects access to Grant School.

 

Based on land area, the proposed business park will generate 19% of the need for the $477,000 bridge at E 1600 Rd, and 13% of the need for the $326,000 culvert at Highway 24/40 (2005 cost estimates). The development should pay for its proportional share of these downstream improvements. If the business park is built prior to these improvements, the increased runoff will lead to more frequent flooding of both roads. The City should identify the intended schedule for completion of these projects.

 

The Airport Business Park proposes to drain 86 acres to Tributary A.  Under existing conditions 39 acres currently drain to Tributary A.  An additional 47 acres of drainage would in fact be added to the tributary.  Implementing the proposed improvements as noted above would be a challenge considering both structures are located in the County, one of which is on a KDOT maintained highway.  Douglas Co. and KDOT would need to participate in decisions relative to these structures.

 

Land Use Planning

 

In addition to the high cost of managing the North Lawrence watershed, landowners and the City should recognize the cost of a future catastrophic river flood. The Corp of Engineers designed the Kansas River levee and reservoir system in the 1960’s to control a specific major flood, with the explicit warning that larger floods will eventually occur. Eventually the river will top the levee, and the impacts in North Lawrence will be similar to the aftermath of the 1951 flood. The reservoir system was never fully completed, and climate change will likely increase the magnitude of possible flood events. These facts should be recognized in the decision to invest public or private funds in the area.

 

It has always been a possibility that the Kansas River could overtop the levee in the event flooding exceeded the design criteria for the levee.  It is also possible for the upper reach of the Maple Grove drainage channel to experience an intense amount of rainfall.  Both of these scenarios would cause severe flooding, but the chances of these events happening are statistically low.  The 1993 flood resulted from a series of events including saturated soil conditions, higher water surface elevations on streams and rivers culminating shortly thereafter with an intense period of precipitation.  In other words it was the “perfect storm” immediately following the perfect conditions for flooding.  Similar conditions were seen on the Kansas River just this past May of 2007; however the lower reaches of the Kansas River did not receive high amounts of rain at the exact same time.

 

Since the 1951 flood several flood control structures have been constructed on the upper reaches of the Kansas River.  The US Army Corps of Engineers constructed the following dams in the early 1960’s:  Wilson, Tuttle Creek, Milford and Perry.  The Bureau of Reclamation constructed the following dams: Norton(Keith Sebelius), Kirwin, Lovewell, Glen Elder and Webster.  Cedar Bluff was nearing construction completion in 1951.  Based on research and the best information available all indications point to a completed reservoir system.

 

Native soils are an asset to landowners in North Lawrence. The sandy-loam, high-infiltration soils reduce runoff and relieve flooding. Covering these soils with impervious surface increases the volume of runoff more dramatically than in heavy upland soils. Building on these soils also permanently eliminates their agricultural value. The Eudora silt loam and Rossville silt loam soil units are both identified by the USDA as crop capability class 1, prime farmland. These factors are not considered in current land use plans. The City should plan for the conservation of these natural resources wherever possible.

 

The City has taken steps to preserve the high-infiltration soils of North Lawrence by the adoption of Ordinance 7100.  City Code Section 20-1204(e)(2)ii limits the amount of fill placed upon developed lots within the floodplain.  Prior to its implementation land owners would bring enough fill to cover the entire lot and raise it out of the floodplain.  The new policy outlines how much fill can be placed on the lot by setting guidelines for setbacks and corresponding side slopes.  This policy allows for preservation of high-infiltration soils and as well as floodplain storage capacity.