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CR 98-57 Accept Feasibility Report Storm Water Flood Analysis-Areas 2,3 & 4April 2, 1998 Proposed Action. Accept Feasibility Report Storm Water Flooding Analysis - Areas 2, 3 and 4 Council Report 98 -057 Staff recommends adoption of the following motion: Move that Council accept the feasibility report on correction of flooding problems in Area 2 - Hilltop Park, Area 3 - Alley between 17 and 18 Avenues, and Area 4 - 13 Avenue North and approve proposed continued action. Overview. In October, 97 staff developed an action plan to address last summer's storm and sanitary sewer problems in several areas of the city. City Council adopted the action plan by resolution on November 5, 1997. The plan included analyzing storm water flooding problems in six separate areas and designing and constructing improvements. This feasibility report analyzes three of these areas and recommends improvements. Primary Issues to Consider. Report recommendations and proposed continued action. • Area 2, Hilltop Park • Area 3, Alley between 17 and 18 Avenues North • Area 4, 13 Avenue North - Maetzold Field Public Information/notice 1998 storm sewer utility budget update Update on other storm water flooding problem areas Supporting Information. • Feasibility Report • Flooding Problem Areas Map Steven J. Stadler, Public Works Director Council Report 98 -057 Page 2 Analysis of Issues. Area 2, Hilltop Park Before we can modify the drainage from the low areas on the east and west sides of Hilltop Park, we must make some downstream modifications. Namely, a detention pond to control the flow rate to meet Minnehaha Creek Watershed District requirements for runoff tributary to the Highway 7 drainage system. Th location of the proposed pond would be just north of 4 Street North and east of 21 Avenue North within the City of Minnetonka. Staff will need to meet with the City of Minnetonka and the Elder Homestead to begin negotiating an agreement regarding shared responsibilities. Staff intends to proceed this year with formulating an acceptable agreement with the three parties involved and designing and constructing the detention pond. Staff will then budget for 1999 design and construction of the new storm sewer piping to serve the east and west low areas of Hilltop Park. Until the new piping system is installed, staff will monitor the east low area and lower the water level by pumping, as necessary. Staff will keep City Council informed as to progress toward design and construction of the detention pond. Area 3, Alley between 17 and 18 Avenues North Storm water flow from this local low area is restricted by inlet capacity and negatively impacted by overland and pipe flow from the 18 Avenue North/1 st Street North intersection area. The report recommends increasing inlet capacity at the low area in the alley and eliminating the negative influences caused by overflow from the west. The report recommends improvements in three phases. Phase I work includes: improving storm water flow by substantially increasing the rate at which water can enter the inlets in the alley, reconstructing the existing alley apron to prevent overland water from flowing into the alley and blocking the existing pipe from the west. Water backed -up at 18 Avenue North would still be able to flow in the gutter to 17 Avenue. Staff proposes to construct these improvements, estimated at $5,000, via a change order to the 6 Avenue North storm sewer project. Phase II work includes increasing the pipe size in 1 Street North and constructing an outlet to Shady Oak Pond. Staff intends to budget for these improvements in 1999. Council Report 98 -057 Page 3 Area 4, 13 Avenue North The feasibility report explains how the south end of 13 Avenue (at the HCRRA trail) receives storm water runoff at a rate far exceeding the capacity of the existing two inlets. The recommendation is to increase the inlet capacity to match that of the connected 36" pipe which runs under the trail to the Maetzold Field system. This would be done by installing eight inlets at the south end of 13 Avenue. This will dramatically improve drainage from this area and should also prevent water from backing up onto the adjacent alley to the east. Staff intends to construct this improvement in 1998 and is currently having construction documents prepared. Following award of the 6 Avenue North storm sewer contract on April 21 d , staff will request a cost from the contractor to construct this improvement via a change order to that contract. If the contractor requests a fair and reasonable cost for this additional work, Staff will request City Attorney concurrence and City Council approval before proceeding with a change order. If a change order is not possible, staff will obtain quotes or bid the work per the City's purchasing policy. • Public Information /notice. With City Council approval of the proposed action described above, staff will mail applicable portions of the feasibility report to residents in each affected area, describe the proposed continued city action, and invite questions or comment. The same residents would be informed prior to construction start. • 1998 Storm sewer utility budget update The 1998 storm sewer engineering and construction budget is $978,500.00 The current 1998 obligations (assuming award of the 6 Avenue storm sewer project) are $850,164.00 These expenditures include engineering, construction and contingencies for the 6 Avenue storm sewer project, storm sewer work included in the 1998 street and utility improvement project and the 9-Mile Creek Maintenance project. It also includes engineering fees for preliminary engineering on the six storm flooding problem areas. Expected additional 1998 expenditures include: • Engineering fees and construction costs for a grading contract to allow additional storm water detention on Oakridge golf course and minor school district regrading. Staff will soon know these costs and will report on them at the April 21st City Council Meeting. Council Report 98 -057 Page 4 • Engineering and construction costs for proposed 1998 work in storm flooding problem areas 2, 3 and 4 described in this report - estimated at $50,000 - 60,000. Update on other storm water flooding areas Preliminary engineering is continuing on area 5 (alley between 8th and 9th Avenues North) and area 8 (2 Street North/Monroe Avenue North). Staff expects to present the report regarding these areas at the Council Meeting on April 21 or May 5th At the April 21 City Council Meeting, Staff will be requesting award of the 6th Avenue storm sewer improvement project (storm water flooding problem area 6). • 1 2 3 4 S um *t - : , : . s • A 1! EE - 1: z /. S te ` L i 1i J : i it l�� ti � �`' = — ; SI , z -. 14 i i ' 1, . 4 � i • ' :4 ����1.,� • 'Ct �"` r a_ •. : .. t ji + 1.0' i •} N Ii 17 !` , ; .�' i.. : ;,... - 7 - ",,:c...6 -,! ' i „ i 1i 1� �I I \` _ l i = 1; It :1 Cd i �i' t .,: j, 1 + j `" ! = .is-? 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I 1 11 I r4 Fi� L V s r 11 ) A M� : • .�.'iKj B 1 7 : r. // !+► i / � 1 � •' • • ,t - c t00 THE CITY HOPKINS MINI HENNEPIN COU 11 L Feasibility Report Storm Water Flooding Analysis Area 2 - Hilltop Park Area 3 - Alley Between 17 & 18 Avenues North Area 4 - 13 Avenue North - Maetzold Field Hopkins, MN RCM File No. 10441 10901 red circle drive • box 130 • minnetonka, mn 55343 • (612)935 -6901 • fax (612)935 -8814 March 1998 rieke carroll muller inc. , ssociates, gineers architects land surveyors equal opportunity employer years of helping build communities 10901 red circle dr. ost office box 130 innetonka, mn 55343 -0130 (612) 935 - 6901 fax (612) 935 -8814 www.rcm - assoc.com March 17, 1998 Mr. Steven J. Stadler, P.E. Director of Public Works City of Hopkins 1010 First Street South Hopkins, MN 55343 Re: Storm Water Flooding Analysis RCM File No. 10441 Dear Mr. Stadler: Enclosed is the feasibility report addressing the storm water flooding impacts to the following areas within the City of Hopkins: Area 2: Area 3: Area 4: Hilltop Park Alley between 17th & 18th Avenues North Maetzold Field - 13th Avenue North The Hopkins City Council identified these three (3) study areas by Council Resolution 97 -104 for storm water flooding analysis. The improvements proposed herein are feasible from an engineering standpoint, in accordance with the City's Comprehensive Storm Water Management Plan, cost effective, necessary to provide an increased level of flooding protection for the property owners adjacent to the study areas and require cooperation between the Cities of Hopkins and Minnetonka in Areas 2 and 3. We are available to meet with the City Council, staff and interested parties to review any aspect of this report. Thank you for providing RCM the opportunity to be of service to the City of Hopkins. Respec ly submitted, CARROLL MULLER ASSOCIATES, INC. Mi - ael P. oertsch, P. ' ./L. S. Ci I/Municipal Department Manager MPF/ka Enclosure Prepared by: Rieke Carroll Muller Associates, Inc. 10901 Red Circle Drive, Suite 200 Minnetonka, Minnesota 553 3 Reviewed by: Date: Date: g) i ‘'T O' FEASIBILITY REPORT STORM WATER FLOODING ANALYSIS AREA 2: HILLTOP PARK AREA 3: ALLEY BETWEEN 17TH AND 18TH AVENUES NORTH AREA 4: MAETZOLD FIELD - 13TH AVENUE NORTH CITY OF HOPKINS, MINNESOTA MARCH 1998 RCM FILE NO. 10441 Steven J. Stadler, P.E., Public Works Director I hereby certify that this plan, specification, or report • repared by me or under my direct supervision and that I am a duly Registered Professional Engineer • er e laws of the . r f ► sota Mic ael P. Foertsch, P. ./L.S. Reg, No. 18139 TABLE OF CONTENTS Section Page Introduction 1 Figure 1 - City of Hopkins Resolution 97 -104 2 Figure 2 - Study Areas 5 Area - 2: Hilltop Park 6 Figure 3 - Area No. 2 Hilltop Park Existing Conditions 10 Figure 4 - Area No. 2 Hilltop Park Proposed Improvements 11 Area - 3: 17th and 18 Avenues 12 Figure 5 - Area No. 3 Existing Conditions 15 Figure 6 - Area No. 3 Drainage Areas 16 Figure 7 - Area No. 3 Hydraulic Profile 17 Figure 8 - Area No. 3 Proposed Improvements 18 Area - 4: 13th Avenue/Maetzold Field 19 . Figure 9 - Area No. 4 Existing Conditions 21 Figure 10 - Area No. 4 Proposed Improvements 22 INTRODUCTION During July 1997, the City of Hopkins as well as neighboring communities experienced flooding of public rights -of way and the adjacent private property. On July 21, areas of Hopkins reportedly received rainfall amounts of as much as 3.5 inches within a 1 -1/2 hour timeframe. This rainfall event is approximately equivalent to a 100 year return storm event. Rainfall amounts of this intensity can cause flooding of localized drainage basin " low areas" as well as areas designed to temporarily flood during rainfall events. In response to these July rainfall events, the City of Hopkins identified eight (8) " problem low areas" for further study. These areas within the City experienced street and private property flooding during the July rainfall events. On November 5, 1997, the Hopkins City Council adopted an "Action Plan" to address storm drainage problems in these eight areas of the City. The "Action Plan" is included as a part of this report as Figure 1. This report includes recommendations to mitigate flooding concerns in three (3) of the eight (8) areas. They are as follows: Area 2 - Hilltop Park Area 3 - Alley Between 17th and 18th Avenues North Area 4 - 13th Avenue North / Maetzold Field These three (3) study areas are shown on Figure 2. 1 • A RESOLUTION STATING THE CITY COUNCIL'S INTENT TO ADDRESS STORM WATER AND SANITARY SEWER AREAS OF CONCERN WHEREAS, the City of Hopkins experienced storm and sanitary sewer flooding during July, 1997, in several areas of the City; and WHEREAS, it is the duty of the City of Hopkins to provide for and maintain the sanitary sewage and storm water systems; and WHEREAS, eight areas of the City have been identified as having experienced problems during the July, 1997 storms; and WHEREAS, the City Council and City staff have already initiated tasks necessary to fully analyze and determine the root of the problems surrounding these flooding events (memo attached); and WHEREAS, the Council is responsible for assuring the taxpayers of Hopkins that they are spending public funds in the most cost efficient and effective manner; and WHEREAS, the studies and investigations currently in place will identify needed improvements to the storm water and sanitary sewer systems. NOW, THEREFORE, BE IT RESOLVED, based on all of the above, the City Council of the City of Hopkins, hereby resolves that it will implement improvements to th sanitary sewer and storm water systems that will improve the conditions in the , identified areas to the extent possible by implementing the attached plan of action: without endangering other areas of the City. Adopted by the City Council of the City of Hopkins, Minnesota, this 21st day of October, 1997. ATTEST: Terry Obermaier, City Clerk CITY OF HOPKINS HENNEPIN COUNTY, MINNESOTA RESOLUTION 97 -104 Charles D. Redepenning, Mayor Problem area Action 1. Shady Oak Pond 2. Hilltop Park low area 3. Alley Between 17th &18th Avenues 4. North of Maetzold Field Contact Stare Stadler Pubic wake Director Phone 6121382 Fax 612939 -1381 Action plan designed to alleviate flooding problems Input sought before City Council approval, Wednesday, Nov. 5 The city of Hopkins has developed a proposed action plan to address storm drainage or sanitary sewer problems in eight areas of the community. The action plan includes projected completion time frames. The Hopkins City Council at its meeting, Wednesday, Nov. 5, will consider the plan, and public input is invited. Written input into the action plan may be sent to the Public Works Director or City Manager's Office. Questions may be directed to Steve Stadler, Public Works Director, 939 -1382 A Dredge Pond and improve ponds edges 1999 B. Construct pond outlet as part of drainage improvements associated with Shady Oak Road reconstruction A Complete drainage improvement project design B. Complete drainage improvement area A Consider alternatives & design improvements to alley drainage B. Complete Construction OCTOBER 1998 A Investigate and design new storm water structure to increase flow capacity from 13th Avenue inlets to Maetzold Field B. Complete construction of improvements City of Hopkins Completion Date 2001 JANUARY 1998 OCTOBER 1998 JANUARY 1998 JANUARY 1998 OCTOBER 1998 sewemrl4.29.doc 4. North of Maetzold Fi Id C. Complete capacity analysis of existing DECEMBER (continued) sanitary sewer collection pipes serving this 1997 area D. Complete repairs to collection pipes, if DECEMBER there are capacity problems because of 1998 defective parts 5. Alley between 8th & 9th A. Confirmation that the proposed 6th Avenue FEBRUARY Avenues North storm sewer project will improve drainage 1998 in this alley 6. 6th Avenue North/3rd A Project design completion Street North storm sewer project 7. Hobby Acres E. Complete sump pump inspections of homes and businesses in this sanitary sewer area and analyze results F. Disconnect any improper sump pump connections in this service area B. Storm drainage improvement project construction completion A Capacity analysis of existing sanitary sewer collection pipes serving this area B. Complete repairs to any defective pipes C. Complete sump pump inspections of homes and businesses in this sanitary sewer service area and analyze results D. Disconnect any improper sump pump connections that are found in this area B. Complete construction of any necessary improvements MARCH 1998 NOVEMBER 1998 FEBRUARY 1998 NOVEMBER 1998 DECEMBER 1998 DECEMBER 1997 I MARCH 1998; NOVEMBER 1998 FEBRUARY 1998 NOVEMBER 1999 AREA NO.2 1® CITY F HOPKINS c II c r i e r k r e ao 1 1 muller associates, inc. engineers • architects • land surveyors • 2 t sERvicE''"' MAINSTREET TH 21 FIGURE 2 STUDY AREAS HOPKINS, MINNESOTA DATE FEB.1998 ) REVISIONS SHEET NO 1, ..■■■■■■■•■ FILE NO. 10441.03 411 AREA -2: HILLTOP PARK ISSUES: The Hilltop Park area located south of 4th Street North and between 19th Avenue North and 21st Avenue North has two local low areas which impact the backyard areas of the homes along 19th Avenue North and 21st Avenue North. During the rainfall events of July 1997, residents adjacent to these areas expressed concerns regarding the rising storm water levels in their backyard areas. The east low area adjacent to the backyard areas of 19th Avenue North, experienced water levels nearly up to the existing walkout elevations of their homes. Residents fear that the outlet may clog and additional rain would cause flooding of their homes. ANALYSIS: Two areas of concerns were reviewed. 1. West low area adjacent to the backyard areas of 21st Avenue North. 2. East low area adjacent to the backyard areas of 19th Avenue North. Field surveys were conducted to verify the following information: 1. Existing topographic information. 2. Elevations and locations of all physical features within the two above referenced low areas. 3. Location, size, elevation of the existing drainage facilities. 4. The tributary drainage areas to both of the low areas. West Low Area The west low area receives direct runoff from approximately 4.2 acres. The 4.2 acres is partly private residential property and a portion comes from the Hilltop Park area. The west low area appears to be drained by an area catch basin with a clay tile drainage system. In reviewing the system, we were unable to determine the outfall of the system. The system was reviewed with City maintenance personnel and they are unaware of the outfall of this system. This area needs to be pumped during heavy rain fall events. The system will need to be televised to determine the outfall location if any. There is sufficient elevation differential between the bottom of the low area and the Trunk Highway 7 drainage system located within the City of Minnetonka. East Low Area The existing 4th Street North drainage system discharges into a ditch which flows northerly along the westerly side of the Elder Homestead development into the Trunk Highway 7 drainage system. The east low area has an existing 12 -inch PVC outlet which City maintenance personnel constructed. This outlet ties into the existing 4th Street North drainage system. The existing outlet is constructed approximately 1.2 feet above the bottom of the low area. A new outlet at a lower elevation is required, along with modifications to the existing 4th Street North storm sewer system, in order to drain this area. The bottom of the easterly lower area is approximately 1.5 feet lower than the bottom of the westerly low area. The east low area receives direct runoff from approximately 2.7 acres. Review of the City of Minnetonka's Comprehensive Storm Water Management Plan The Hilltop Park sub - drainage area is designated as area 99 in the City of Minnetonka's Comprehensive Storm Water Management Plan. Minnetonka's Storm Water Management Plan identifies this area as being tributary to the Trunk Highway 7 drainage system and states the following: "The area located around the intersection of Minnesota Highway 7 and Minneapolis St. Louis Railroad (Ponds) 99 and 101 has an incomplete and possibly an inadequate outlet system. It does not appear likely that flood damage would occur to buildings in this area. However, flooding of Minnesota Highway 7 could occur. Berms are proposed to be constructed in watersheds in 99 and 101 to provide more storage. With the additional storage, the existing 54" pipe in watershed 106 appears to be adequate to drain watersheds 99 and 101." 7 The existing 54 -inch pipe which the City of Minnetonka's comp plan references is not the restriction in this area in the storm water drainage system. The existing restriction is a 24 -inch storm sewer located along T.H. 7 where the abandoned railroad grade crosses the highway. In reviewing the Hilltop Park area with the City of Minnetonka staff, they stated that any change in the existing drainage patterns within this sub - drainage district, would trigger the need to incorporate rate control measures into the storm water drainage system. This requirement is being placed on the entire drainage area tributary to the T.H. 7. The Elder Homestead development Located north of Hilltop Park within Minnetonka is planning to expand its existing facility. The planned westerly expansion will encroach on an existing City of Hopkins drainage and utility easement necessary to drain 4th Street North as well as the easterly portion of the park area. The Elder Homestead facility would be required to modify the existing drainage system which serves this area. In reviewing the proposed expansion with City of Minnetonka staff they stated the Elder Homestead representatives appear willing to cooperate as much as possible to develop a feasible solution to the storm water concerns in this area. The City of Minnetonka has expressed willingness to participate to resolve the storm water drainage issues along T.H. 7 as well. RECOMMENDATIONS: There is sufficient elevation differential between the low areas of Hilltop Park and the existing drainage facilities along T.H. 7 to provide a gravity storm water outlet to service the park area. The T.H. 7 storm water drainage facilities are the designated receiving storm water system for the Hilltop Park area as identified in the City of Minnetonka's Comprehensive Storm Water Management Plan. The Minnehaha Creek Watershed District has placed storm water run -off rate control requirements on all storm water system modifications which are tributary to the T.H. 7 drainage facilities. The Minnehaha Creek Watershed District is restricting all storm water flows into the existing system to pre - modification levels or less. • The City of Hopkins will be required to restrict the storm water flows from the park area to less than or equal to existing conditions. In order to provide drainage facilities for the park area storm water 8 detention will be required. The City of Minnetonka has identified the area located westerly of the existing Elder Homestead facility between T.H. 7 and 4th Street North as a potential location for storm water detention prior to discharge into the T.H. 7 drainage system. The construction of the facilities to serve the Hilltop Park area is recommended in three phases. Phase 1 would include constructing a storm sewer pipe from the east low area, north to the R/W line of 4th Street North, westerly along the 4th Street North R/W line to a point where the storm sewer system could discharge into a detention basin Located westerly of the Elder Homestead between T.H. 7 and 4th Street North. After 7th and 4th Street North, and construction of the detention basin prior to discharge into T.H. 7 drainage system. Phase 2 would include the outlet for the west low area of Hilltop Park. This outlet would be constructed northerly and connect to the storm sewer facility constructed along the southerly R/W line of 4th Street North with Phase 1. The third Phase of the improvements would be completed with the future reconstruction of 21st Avenue North. Phase 3 will not only include the storm sewer facilities necessary to drain 21st Avenue North but will also provide the opportunity to drain a lower area located westerly of 21st Avenue North. The cost of the Phase 1 improvements is estimated at $150,000 including engineering and administration. The ponding portion of the improvement cost is estimated at $25,000. Phase 1 improvements can be best carried out as a stand alone project or combined with similar work for bidding. 9 rieke carroll muller associates, engineers • architects • land surveyors T/CSTG.926.8 • INV.920.2 W INV.920.65 E 1 T/CSTG.921.3 INV.917.68 T/CSTG.926.0 INV.922.8 N INV.922.2 W 7 JiilJ • -• - a .1 = • ^ = • ?Th.. 21" CAPACITY 32 cfs_)___ tilk7 - - , • ^: • • • • ---- ----- --- ---..---. . ___ ir 1 ! , . i - '•:, - :-.:-.7 - --:--. • 4 i! ; : : , ---::< 1 !, 1 SCALE: 1" = 100' liy; •j4L, ,;)4 INV.921. 36" 0 6.8% T/CSTG.924.5 INV.918.8 92 3 1, ce o , • I.- OVERLAND 1 FLOW K, 90 cfs ) _LJ 3RD STREET NORTH AREA NO.4 EXISTING CONDITIONS HOPKINS, MINNESOTA 27 CAPACITY 24 cfs DATE MAR.1998 .30 - CAPACITY ( 9 55 i 4 j FILE 10441.04 r \ ,n • \ q.t , 1 i 1 1 - 1/` -' 1 ' \ ",,,:.• 'Nk ' St . I ......-_-_, A • -... :-----•..... ,, 1 / i ' - II • - -t— ' , 1 SCALE: 1 = 100' x 7WC, .LJT ; 97.P 7 21" CAPACITY 1%2 cfs 492 • 1,-+ i LI .,1 ;11 _ 4 ; / \ •••••• 1 4 T/CSTG.926. -- INV.919.25 .• • V.919.6 E INV.921. 36" 0 6.8% T/CSTG.924.5 INV.918.8 3 3' MI : 1: .1 to - —7.7- -',.- — ---- - 7 -7- - . - - - -1:, 0 6 ›e - _— • p Z i 1 \ g , - i :' I'l : • I i 4 Irk ii4 Ht i ____...v- _ _ 30A-PACITY _------ -- - --- 3RD STREET NORTH - V CAPACITY 24 cfs 2 ,D ' 7tAfs 12" 3. C el c r i e r k r e aoli muiler associates, inc. engineers • architects • land surveyors FIGURE NO.10 - .. -;-:::,,-::- -.... s. 1 T/CSTG.920.8 T/CSTG.926.0 --... --..‹:. :. -- , ., .... is. NV.922.8 N ,,, INV.922.2 W ' : . N -... .-... -",.‹....., \O 0 'W.:. T/CSTG.921.3 INV.917.68 REVISIONS SHEET NO. 111 I I 1 11 1 T/CSTG.926.8 11 ; : IN V.920.2 ' L_ • IN V.920.65 W E en 01 AREA NO.4 PROPOSED IMPROVEMENTS HOPKINS, MINNESOTA (DATE MAR.1998 RECONSTRUCT STREET ADDITIONAL INLET fr ,,ii ,,,.. Al?ACITY_ ! -. II 1 ' !. ; ; '.-i 1 1 4 , \WO ;I 1 , 1 1 :j 1 i PI i I i •,`) ' , 4 ' I ,-1, / II 4 • '' j rl _ ■ ■ i ,..., \ - ri 2nd STREO ; , 1 1 otr....„.:1,17.77._1114 r 9.34_ 7 t • 1 11 1 FILE NO. ) 10441.04 r X AREA -3: 17TH AND 18TH AVENUES ISSUES: This local low area is located in the alley between 17th and 18th Avenues, south of 1st Street North (Figure 2). There is a 12" storm sewer system provided to drain this localized low area. This storm sewer system connects to the system in 1st Street North which connects to the 17th Avenue North system. This area floods whenever the storm water run -off exceeds the inlet capacity of the system. During July 1997, this problem was exaggerated due to street construction at the intersection of 1st Street North and 18th Avenue North. ANALYSIS: RCM conducted a field survey of the localized low area in the alley south of 1st Street North between 17th Avenue and 18th Avenue to verify existing storm sewer elevations on 1st Street as well as the topography adjacent to the low area in the alley. The localized drainage area directly tributary to the low point in the alley is 2.5 acres (Figure 5). There is an inlet at the low point (elevation 925.9) with a manhole ring casting and a Neenah R -4370 type D heavy duty drainage grate. The inlet capacity of this drainage grate with 0.6 feet head (elevation 926.5) not clogged is 3.35 cfs. The drainage grate has 1 1/2 -inch wide slotted openings which will allow the opening to become easily clogged. For design purposes, 1/2 clogged condition of the inlet capacity is assumed which lowers the inlet capacity with 0.6 feet head to 1.7 cfs. The 0.6 foot head or water level of 926.5 was selected to protect existing garages. The 2.5 acre drainage area generates 2.9 cfs, 3.5 cfs and 4.1 cfs runoff based upon a 2 year, 5 year and 10 year return period. Storm sewer piping from the catch basins in the alley is a 12 -inch at 0.4% north to 1st Street, then a 12 -inch at 0.73% east to 17th Street that connects to a 27 inch storm sewer drainage south on 17th Avenue. Capacity of the 12 -inch full pipe is 2.4 cfs. Surcharged to a water level of 926.5, the 12- inch pipe can carry 4.0 cfs. A full pipe has the capability to handle a 2 year return frequency but surcharged to 926.5 has the capacity to carry a 10 year return storm. 12 The localized low area is adjacent to a low area at 1st Street North and 18th Avenue. This intersection collects surface water from a 45 acre drainage area (Figure 6). Some of this surface runoff is collected in the storm system on 17th Avenue but the majority is collected in the storm system along 1st Street. The surface water runoff from the 45 acre drainage area is 43 cfs, 54 cfs and 63 cfs for a 10 year, 50 year and 100 year return frequency. The existing storm sewer carrying surface water away from 1st and 18th Avenue is an 18 -inch to the west and a 12 -inch to the east. The 12 -inch connects to the 17th Avenue system and drains the alley area as well. If we use elevation 926.5 as the water level in the low area of the alley and surcharge the pipeline on lst accordingly, the storm sewer capacity of the 18 -inch at 0.04% grade west of lst and 18th is 14 cfs and the capacity of the 12 -inch east on 1st is 4.0 cfs. All contributing flow to these low areas in excess of 18 cfs will pond higher than the 926.5 elevation (see Figure 7). RECOMMENDATION: There are three situations which cause localized flooding in this area. The first is inadequate inlet capacity in the alley area to allow the storm water to enter into the existing storm sewer pipe system. The second is the overland flow which collects at this location when the existing storm sewer pipe system is at capacity. The third is there is no outlet control at Shady Oak Pond. We recommend improvements to this area in three phases. Phase 1 construction would be to increase the inlet capacity in the alley area to equal that of the existing pipe capacity. The second part to Phase 1 would include the reconstruction of the concrete apron entrance to the alley to contain the overland flow within 1st Street North easterly to the 17th Avenue North drainage system. The third part to Phase 1 would be to bulkhead the existing storm sewer connection from the west which allows the 18th Avenue North and 1st Street North pipe system to back flow into this alley area. 13 Phase 2 of construction would include the following: • Increase the pipe size from the alley to the existing storm sewer system in 17th Avenue North, • Lower the intersection of 18th Avenue North and 1st Street North to allow for the overland drainage to this point to enter this storm sewer pipe system, and • Increase the pipe size of the existing storm sewer system from 18th Avenue North to Shady Oak pond. Phase 3 construction would include the installation of outlet control at Shady Oak Pond. The outlet can be constructed before the Shady Oak Road upgrade or in conjunction with the planned upgrade of Shady Oak Road in 2001. Given the past flooding experienced with Shady Oak Road, the City should seriously consider the pond outlet control along with the pond improvements identified for 1999. The cost of the Phase 1 improvements is estimated at $5,000 including engineering and administration. This improvement can be best be constructed as a change order to an existing City contract. 14 X111 rieke carroll muller associates, inc. III engineers • architects • land surveyors ( FIGURE NO.5 ) AREA NO.3 EXISTING CONDITIONS HOPKINS, MINNESOTA (DATE MAR.1998 ) REVISIONS SHEET NO. 1 FILE NO. 10441.03 5TH ST SERVICE ROAD MAINST ST. z 1.1 1ST ST. N. SERVICE FIGURE NO.6 • ® .t r r k r e ao associates, inc. engineers • architects • land surveyors as OVERLAND FLOW DIRECTION STI-1 AREA NO.3 DRAINAGE AREAS HOPKINS, MINNESOTA REVISIONS , o1.■■•■■•■••• • ■■••■•■• 0 (DATE MAR.1998 "to SHEET NO ( FILE NO. 10441.03 I - >- v Z r 0 W> zz 00 ce LL. z C I11 rieke Carroll muller associates, inc. engineers • architects • and surveyors Fir.,1)RE - 2J -3S ='LC'T 1 'N, 3441 05 ab08 >IVO AGVHS ■ '3AV HIL '3AV HJ 9 i . 3AV H16 I. / •3AV HIO N ( 0 N) 0) cri z o 0 0, z FIGURE NO.7 AREA NO.3 HYDRAULIC PROFILE HOPKINS, MINNESOTA S F- D 0 V J V ) W J LL 0 0 REVISIONS MAR.1998 SHEET NO. FILE NO. 10441.03 S 1 (C 1 ,.•‘, 19th 18th , • AVENUE r7 1 1 E.; i• AVENUE X INV.924. • I 1-- INV.923-4 ' , • 1 t" / 1 ) I as: • 17th c 1 c rie r k r e aoil muUer associates, inc. engineers • architects • land surveyors is< ADDITIONAL INLET CAPACITY E: IFSTG.925. (*; AVENUE RECONSTRUCT APRON • — f Lc; — 9,30 1 2 • r, INV.941.9 -J s> FIGURE NO.8 AREA NO.3 PROPOSED IMPROVEMENTS HOPKINS, MINNESOTA ( INV.922.8 77 • REVISIONS DATE MAR.1998 2- BULKHEAD 17175 73.6' - : INV.9 SHEET NO. FILE NO. 10441.03 AREA -4: 13T11 AVENUE/MAETZOLD FIELD ISSUES: The 13th Avenue area north of Maetzold Field has flooded several times after the July 21, 1997 storm. Storm water is collected in two inlets at the south end of the alley between 12th and 13th Avenue and two inlets at the south end of 13th Avenue. This water flows via a storm sewer pipe system under Maetzold Field during minor rainfall events and overflows, by design, onto Maetzold Field during major rainfall events. City personnel reported problems in this area with clogged inlets and the appearance of no flow from the alley into the 13th Avenue storm sewer system. ANALYSIS: The existing storm sewer system (see Figure 9) consists of a 30 inch RCP under the old abandoned railroad grade. The grade is now owned by Hennepin County and operates a trailway along the corridor. Just north of the grade at the south end of 13th Avenue are two catch basins and a 12 inch PVC pipe which extends easterly to the alley area between 12th and 13th Avenue's, south of 3rd Street. Approximately 1.9 acres are tributary to the south end of the alley. This 1.9 acres generates approximately 3.6 cfs during the 10 -year storm and approximately 5.3 cfs during the 100 -year storm. The local area tributary to the 13th Avenue system low point, adjacent to the railroad grade, south of 3rd Street is 2.1 acres. This area generates 3.8 cfs during the 10 -year storm and 5.9 cfs during a 100 -year storm. The total drainage tributary to this point is designated as area "CB" in the City's Storm Water Management Plan. Area "CB" generates an estimated flow of 115 cfs during the 100 year storm. The existing capacity of the storm sewer system at the intersection of 3rd Street and 13th Avenue is calculated at 24 cfs. Overland flow not collected in the storm sewer system, approximately 90 cfs (115 cfs -24 cfs), then flows overland easterly along 3rd Street and then southerly along 13th Avenue to the railroad grade. The capacity of the 36 inch storm sewer system connecting to the Maetzold Field system is approximately 65 to 80 cfs. The restriction at this point is the inlet capacity. This restriction in inlet 19 capacity causes flooding which in turn over flows into the alley area between 12th and 13th Avenues. The inlet capacity of the existing catch basins can not accommodate estimated flows tributary to the area. RECOMMENDATION: At the south end of 13th Avenue, remove the existing structures, a portion of the street and replace with 8 -inch high concrete curb and new catch basins which will increase the capacity thus allowing the surface runoff to enter the existing 36 -inch pipeline. We would recommend using catch basin castings similar to Neenah R3246-AL like those proposed on the 6th Avenue project because of the large square foot grate opening. These castings with 8 inches of head can take 7.9 cfs each - 1/2 clogged (see Figure 10). COST The costs associated with the recommendation includes removing two catch basins and 18 -inch pipe between these structures and approximately 30 feet of 13th Avenue. By placing three catch basins on each the west and east side and two at the toe of the rail -bed slope and using 8 -inch high curb, a sump will be provided and enough inlets constructed to collect the surface water. The estimated construction cost is anticipated to be $31,500 including engineering and administration. This work can best be accomplished as a change order to an existing City contract or combined with similar work for bidding. 20 - - , ......,---- - CT - " — r------ \, , ,, \ , 6 `■ \:; \ , ‘ ' 3'1 ‘ 19:\ )d \ ) it / / i , ' 13------ ---- ) to \ \ \ \ f/ ( 'P ( „..—.......... j 6s3 ' \ ,....,... , “........_,..._.:-- r-;„ - 1 ,-: -"."-<< 2.... ,...-.. , ,. 0 /' \\\\\11 ' \ 8 ,.,, \\\ \\'' . ' 4, rl <T- / / '‘‘,::::-.. :---- ----- \ \ ----- i I i ‘° \‘' \ \‘\ \ 1 \ -........_____ ,-, ',. .. ',11>_ ‘s!. 0 (■ ?/' ---_ ___.--- I `,-----------7-------:'="------..\ 2 1 ( v\ , 6 , , --77‘1 1 , 6 1 .f■ ..,,) ______LI l...4 „" ., , ,, / // / "-' o...1,:.:1 7 0, ,,//, ii / D e„, - Cs 0 .../ X (D 'Z' . j , r, , z,":1 ,L.■ ;,?, < -. " ;"/// „ • 1 '---"''- / • 43 • . 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'I l:.:l \:::::li .‘...1.,11:1 L: :::1....„:1:1Th.,,,,,.:' l'./ 7 ' L.,..,,,... .-...,....., 1 — A O- / 4, r ' ' I ' i I E• ,•. :0( ..,, , !,;,-•■71-■-• 1 \ je■NINENIEN, AINIONNIMPOne AVENUE .NORTH it 6 4 ,11•11.‘ REVISIONS DAM OCSCRIIMON FIGURE NO.4 0 ( AREA NO.2 - HILLTOP PARK PROPOSED IMPROVEMENTS HOPKINS, MINNESOTA A ! tompomi ( I WISPY COM, iN, OPP PV/1 SPIC/MATION OP RENON? WAS IRENNCO PV IC OP WPM NV piPf,/ soocovisrto. AND INA ■ AN a pu.v NMS•PPPO mom,. moo oc loos co roo PTAK or NOOPPOIN POCWO. FOCOTSES Pitattald9P1 - 1 --j \fl -41 1; 4 i, in [1C111 rleke cat-roll mutter associates Inc. • architects • ertgheers • Ind surveyors •