Lee's Summit

Provide the advisory speed signs for the TTC on the shoo-fly based on the horizontal radii. The contractor should not be required to assess the appropriate speed from an EPG reference.

Please refer to comment #10 of the applicant letter dated June 19, 2018. The response to comments appears to be directed toward the stilling basin design at the end of the triple culvert, rather than the outlet of the 5x5 RCB beneath Summit St. We saw no changes were made to the design, and are concerned about the effect that a 5x5 box culvert will have at the discharge point, when installed at a slope greater than 4%. This will be flowing supercritical, and a simple MoDOT Type 3 ditch liner is in our opinion not sufficient to manage the energy at the end of this RCB. There may be intervals where the normal pool elevation is lower than normal, and we do not feel the MoDOT Type 3 ditch liner is adequate to absorb the energy of the stormwater discharge. Is there a way to lower the slope of this box culvert to eliminate this concern? What is the rip rap size, and where is the geotextile fabric needed? If you are going to specify "MoDOT Type 3 Ditch Liner", you will need to provide a detail of this feature in the plans, and provide a reference to this detail on the plan view. Finally, what is the proposed grading at the beginning of this box culvert (i.e., near station 2+47)? As shown, it is difficult to determine what the proposed grading will be in this area.

Please refer to comment #12 of the previous applicant letter. A "MoDOT Type 3 Ditch Liner" is specified, but no such detail is provided in the plans. Geotextile filter fabric was not shown, and must be shown as per City of Lee's Summit requirements. Rip rap size was not specified, and referencing the size in the stormwater report is not sufficient since contractors and inspectors do not read these reports. Finally, MoDOT Type 3 Ditch Liners do not appear to meet the requirements shown on Sheet C4.2. This appears more in line with a MoDOT Type 4 Ditch Liner than a Type 3 Ditch Liner.

Please refer to comment #16 of the previous applicant letter. Please label the 100 year hydraulic grade line as "clogged condition of primary outlet works - 100 year hydraulic grade line" or equivalent language. In addition, the following questions should be answered prior to consideration of your request to allow for non-gravity flow for the 100 year, clogged condition event: 1) what is the hydraulic grade line within the triple PPP culvert for the un-clogged condition (please show graphically on the profile view, with appropriate notes such as "100 year hydraulic grade line with primary outlet works functioning normally", or equivalent language), 2) are all conditions set forth in Section 5606.3 "Pressure Flow" met, such as the condition that watertight joints capable of withstanding the internal surcharge pressure are being used, appropriate energy losses for bends, transitions, manholes, junction boxes, inlets, and outlets used in the computation of the HGL, and Bernouli's equation was used in the computations?

Provide the advisory speed signs for the TTC on the shoo-fly based on the horizontal radii.

Provide the 16th Street restoration plans/details.

The "Final Stormwater Management Study" dated June 8, 2018 contains a confusing statement in the first section (page 4). Please clarify that the composite curve number of 74.76 for the proposed site is the "existing condition curve number for the proposed site" (or equivalent language).

Page 8 of the Stormwater Study: Table 6 includes a column for the "100 year Low Flow Bypass". What does this mean? Is this supposed to represent the 100 year clogged condition? If so, shouldn't the elevation be 1010.4 as shown elsewhere in the report? Does this represent something else?

Page 9 of the Stormwater Report: The second to last paragraph on this page refers to "...a rip rap basin to be constructed to reduce the effects of downstream erosion". Shouldn't this refer to a rip rap stilling basin, designed in accordance with HEC-14, third edition? Where are the design calculations for this stilling basin?

Page 10 of the Stormwater Study: Since this a summary and recommendations section, we need to see a specific statement that the retention basin meets or exceeds the requirements of Section 5600 of the Design and Construction Manual, and in particular, the Comprehensive Control Strategy listed in this document.

As discussed in your response to comment letter, the temporary shoo-fly is currently in design. The plans cannot be approved until this has been completed.

Sheet C4.1: Although the grading for the retention basin is shown, and there are various spot elevatons called-out showing the top of the dam is at 1011.04, there are questions concerning the top of the dam on the east and west side of the retention basin. No elevations were provided in these areas, so questions remain concerning the top of the dam in these areas. Please show the elevations on key contours in these areas, and ensure the top of the dam is designed no less than 1011.04 feet.

Sheet C4.1: Although a detailed grading plan has been provided for the retention basin, it appears that the pre-existing drainage patterns will be altered in such a way that the drainage along the dam slope shall be directed directly towards the off-site properties to the south. Without existing contour elevations on the off-site properties to the south, it is difficult to determine whether this will have an adverse impact on these properties. Please show the existing contour elevations of these off-site properties, and provide a means of drainage to these properties which will not have an adverse affect on them.

Sheet C5.2: Please show the grading in the vicinity of the outlet structure serving the retention basin. The grading must match what is shown on the detailed grading plan shown elsewhere in the plan set.

Sheet C5.2: Addtional cross-section views should be provided for the rip rap stilling basin shown at the end of the triple PPP. Perhaps Section A-A shown longitudinally, and Section B-B, C-C, D-D, E-E, etc. shown transverse? The section lines should be shown on the plan view. In addition, horizontal dimensions were missing on portions of this stilling basin. The overall length and width are provided, but this is not a rectangular basin. Please show all dimensions necessary to build this feature.

Sheet C5.5: Is the submerged portion of rip rap at the end of the RCB sufficient for energy dissipation? It appears only 10 feet of rip rap will be available for the submerged portion. What calculations have been provided to support this length? Stormwater discharge at this point will be supercritical, and we feel this is not sufficient for energy dissipation, even though the outlet will be submerged in most instances. In periods of pond elevation being below normal, this will be especially important, since the rip rap will likely fail during the first significant rain event.

Sheet C7.2: A depth dimension was missing from the toe wall.

Sheet C7.4: The energy dissipator detail is lacking the following details and/or features: 1) additional cross-sections in the transverse direction (see previous comment), 2) rip rap size, based on the design (see previous comment related to design), 3) material used for the toe wall (is this concrete), 4) the leader line on dimension "1.20'" is missing an arrow, 5) method used to drain stagnant water (e.g., perforated drain tile daylighted further downstream?). Finally, we have concerns that the stilling basin length and depth will be sufficient to create a hydraulic jump within the depressed stilling basin. Please see previous comments related to design calculations. Sufficient design calculations must be provided showing how the various dimensions were obtained.

Sheet C.7.4: In addition to cross-sectional views of the stilling basin, a larger plan view should be provided for this important feature. This plan view should include all the necessary dimensioning necessary to construct this feature.

Were other alternatives explored for energy dissipation at the end of the triple PPP? There may be better ways to provide energy dissipation than a rip rap stilling basin.

Sheet C7.8: A west wall elevation view appears to be missing. Are there any weir openings on the west wall?

The hydraulic grade line for the clogged condition, 100 year event must be shown within the triple PPP. This is due to the fact that this is the emergency overflow system. The system should be capable of managing this in a regime of gravity flow, in accordance with Section 5603.1 of the Design and Construction Manual. Pressure flow may be allowed on a case-by-case basis, but the City will not support such a request in this instance.

For all other storm lines, the hydraulic grade line must be shown for the design storm event. The same criteria as discussed above (i.e., gravity flow) should be shown for each storm line, unless justification can be provided that the storm line can be designed under a regime of pressure flow, and provided that the hydraulic grade line for the design storm is a minimum of 6 inches below the lowest opening in the system.

The street crossing at Summit Street (i.e., storm line shown on Sheet C5.5) should be designed for a minimum 25 year storm event, under a regime of gravity flow. The hyraulic grade line for this storm line was not shown, and should be shown on the profile view in the same manner as all other storm lines within this plan set.

What is the upstream headwater depth for the 100 year event at the Summit Street crossing? There is concern that this RCB will create a adverse effect on the upstream property.

Easements for drainage and water must be provided prior to approval of the plans.

Shoo-Fly requires more detail in the plans. The alignment should be established in the plans, rather than referencing another planset. The width should be dimensioned, temporary traffic control plan detailed (not TBD in coordination with inspections), and surface (and typical section) shall comply with Fire Department requirements capable of accommodating emergency vehicle apparatus weight.

The "Final Stormwater Management Study for the Grove at Lee's Summit", dated May 3, 2018 (hereinafter referred to as "the stormwater study") appears to be missing the following items: 1) discussion of wetland and USACE issues, 2) an existing condition drainage area map, with points of interest defined for each subarea, including any off-site contributors to the drainage areas with contours, 3) a proposed condition drainage area map, with the same information listed for the existing condition map, 4) elevation-area-volume curves for the storage facility including notation of the storage volumes allocated to runoff, sediment, and permanent residual water storage for other uses (wet basins only), 5) inflow hydrographs for all (1, 10, and 50-percent) design storms, 6) stage-discharge rating curves for each emergency spillway, primary outlet works and combined outlets and overflows, 7) routing curves for all (1, 10 and 50-percent) design storms with time plotted as the abscissa and the following plotted as ordinates: following plotted as ordinates: • Cumulative inflow volume • Cumulative discharge • Stage elevation • Cumulative storage

The stormwater study did not appear to discuss details concerning the emergency spillway. Will the emergency spillway be incorporated into the riser structure, or will a separate emergency spillway be constructed (e.g., earthen spillway)?

The stormwater study discusses blockage of the low flow orifice (i.e., the 8" orifice). Section 5600 of the Design and Construction Manual requires that the 100 year water surface elevation be calculated assuming 100% clogging of the primary outlet works, and assuming zero available storage. In other words, it does not appear this was taken into account during design of the detention basin or the emergency spillway.

Section 5600 of the Design and Construction Manual has specific requirements for an effective emergency spillway system. It must have a crest elevation of no less than 0.5 feet above the 100 year water surface elevation (unclogged primary outlet works condition), and there must be a minimum of 1.0 feet of freeboard between the 100% clogged-condition 100 year water surface elevation and the top of the dam. It does not appear these conditions have been met, since there appear to be no calculations showing the 100% clogged/zero available storage water surface elevations for the 100 year event.

The stormwater study did not appear to discuss sedimentation allowance within the basin in accordance with Section 5600 of the Design and Construction Manual. This would include calculations of sedimentation of not less than 5 years accumulation.

Will the pond include fish? If so, please be aware of the depth requirements contained in Section 5600.

A sediment forebay appears to be missing from the pond. Please see Section 5600 of the Design and Construction for specific requirements.

Drawdown provisions within the retention pond appear to be missing (i.e., siphon or drain). If these are not being utilized, discuss in the report and provide justification for their exclusion. This provision is needed in case the water level in the pond needs to be lowered during an emergency situation, such as a dam breach or other issue.

The outlet structure appears to be missing anti-clogging measures. In accordance with Section 5600 of the Design and Construction Manual, a reverse slope pipe which draws from below the permanent pool, or other method must be utilized. As proposed, the outlet structure will likely clog on a frequent basis.

The stormwater study contradicts the detention basin outlet structure shown on Sheet C7.8. There are too many discrepancies to list in this comment letter, so we are asking that a thorough review be conducted. Orifices are called-out in the stormwater study, while the plans appear to show weirs. This must be reconciled.

The shoo-fly appears to propose MoDOT Type 5 for the surface course. This design, including the simple subgrade design (i.e., compacted native subgrade) does not appear to be capable of supporting the weight of emergency vehicles. As design must be presented showing how this will be capable of supporting the weight of a fully-loaded fire apparatus truck.

Sheet 7.2: The PPP pipe appears to be laid on native subgarde, according to the detail. The City requires an aggregate bedding be placed.

Sheet 7.2: A mud mat is not desired when using pre-cast box culvert structures. If pre-cast, then do not specify its use. If cast-in-place, then a mud mat is required. It must be 6 inches thickness rather than the 4 inch thickness shown in the plans.

Where are the calculations for energy dissipation at the end of the triple PPP? Will the flow be supercrtical? If so, additional energy dissipation structures are required. Rip-rap is not sufficient in this instance. Keep in mind that the calculations of velocity on the storm calculation tables would appear to represent steady sub-critical flow rather than supercritical flow.

The triple PPP culvert appears to be too shallow beneath the roadway. It would appear these culverts will tend to float, and also are not capable of withstanding loading requirements for the roadway. It is likely that a RCB structure is warranted at this location.

The current storm drainage beneath 16th Street daylights into what appears to be a natural stilling basin. The proposed replacement does not appear to incorporate this design element into the design, and there is a significant concern about downstream erosion issues.

An enlarged grading plan for the retention basin is warranted. Sheet C4.0 shows the grading for the retention basin, but contours are shown very close to each other, with no clear definition between successive contours.

Please be aware that an as-graded and as-built plan for the detention basin shall be required prior to issuance of a Certificate of Substantial Completion. This includes both the grading, and the outlet structure construction details.

The hydraulic grade line for the 100 year storm event was not shown on the profile views for any of the storm lines. This is required.

If the hydraulic grade line for the 100 year event is above the crown of the pipe, then justification must be given for this design. Section 5603.1 of the Design and Construction Manual specifies that "...pressure flow may be justified in certain instances." If the hydraulic grade line for the 100 year event is above the crown of the pipe, then justification must be given for this design.

Sheet C5.5: The outlet for storm line for the Summit Street RCB is shown in what appears to be supercritical flow at the outlet. Although this is partially submerged at the end of pipe, there may be significant issues with this design. For example, it is likely that submerged erosion will occur within the retention basin, and will eventually lead to undermining of the end section and eventual failure.

Sheet C5.6: Are these calculations assuming steady uniform, subcritical flow? If so, then it would appear many of the calculations of velocity at the end of pipe are in error?

Have all the necessary drainage easements, water line easements, and utility easements been obtained?

Sheet C7.7: A 4' by 5' Reinforced Concrete Box is shown. What does this detail refer to? Where is the plan view? Are there pipes connected to the box?

Sheet C7.8: Significant issues remain unresolved concerning the details shown on this sheet. Please see previous comments related to the detention basin outlet structure. If elevations are shown, they must be clearly identified with a specific orifice or weir or other opening. As shown, it is impossible to say with any certainty what these elevations represent. In addition, they do not agree with the stormwater report.

Plan and Profile Sheets for Triple Culvert: Please see previous comment related to the proximity of the PPP to the pavement. In addition. it appears the wall thickness was not accounted when drawing the pipe. In other words, the pipe will be even closer to the surface than shown.

It is our understanding that the "cut-off channel" to the east of the 102 SE 16th St. will be piped, and eventually connected to a box within the triple culvert system. It is our understanding these plans will be provided as part of the 16th Street project. As such, no approval for the Mass Grading and Stormwater shall be granted until the 16th Street plans have been approved. Simultaneous construction shall be required, since this is integral to the entire system.

Concerning the Downstream Hydraulics: Was the 100 year 100% clogged condition for the primary outlet works (i.e., all orifices and weirs excluding the emergency spillway) considered when calculating the capacity of the downstream triple culvert? Was the assumption of "zero available storage" (i.e., essentially, was the 100 year event upstream of the retention basin) taken into account for this condition? In accordance with the Design and Construction Manual, if this triple culvert is being utilized as the emergency overflow system, then it must be sized to handle the 100 year storm event upstream of the retention basin. In other words, the upstream hydrograph must pass through the triple culvert without surcharging.

Please submit a hardcopy version of the stormwater study. The electronic version contained a font type that was not recognized, and the resulting printout contained printing errors.

Please define "BHC Watershed" mentioned in the stormwater study.