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HomeMy WebLinkAboutA004 - Council Action Form dated August 14, 2001 ITEM DATE: 08/14/01 COUNCIL ACTION FORM SUBJECT: RESOLUTION TO APPROVE THE PRELIMINARY PLAT FOR SOUTH FORK SUBDIVISION (DOTSON PROPERTY), GENERALLY LOCATED NORTH OF COLLEGE CREEK, SOUTH OF THE WEST-SIDE HYVEE GROCERY STORE, EAST OF JEFFERY LANE, AND WEST OF VILLAGE DRIVE AND CONTAINING APPROXIMATELY 56.07 ACRES. BACKGROUND: The developers are requesting approval of a Preliminary Plat for a subdivision with 150 lots to be developed under Suburban Residential zoning. This development will also include five outlots that will be transferred to adjoining single-family homeowners for inclusion into their existing lots and two outlots for open space. The total gross acreage included in this subdivision is 56.07 acres, and it is located north of College Creek, south of the west-side HyVee grocery store, east of Jeffery Lane, and west of Village Drive. Lots 1-7 and 17-21 are proposed to be developed with multifamily residential units. Lots 27-63 are intended to be developed with single-family attached homes. The remaining 101 lots are intended to be developed with single-family detached homes. Development is to occur in two phases. The First Addition includes the northwestern portion of the site and will include 27 single-family detached lots, 11 single-family attached lots, and 12 multifamily lots. The Second Addition will constitute the remainder of the development. The subject property is currently undeveloped with the exception of an existing farmstead and barn that will remain for the First Addition. The house and barn will be removed at the time of development of the Second Addition. The west-side HyVee grocery store is located to the north. The land to the east and west is mostly comprised of single-family and two-family residential units. College Creek and the proposed location for a new school facility of the Ames Public School District are located to the south of the subject property. Concurrent with this request for approval of the Preliminary Plat is a request to approve the rezoning of this property from "A" (Agricultural), "RL" (Residential Low Density) and "RM" (Residential Medium Density) to "RL" (Residential Low Density), "F-S RL" (Suburban Residential Low Density) and "F-S RM" (Suburban Residential Medium Density). A Master Plan for the development of this site is included with the rezoning request. ANALYSIS: Annexation and Land Use Policy Plan (LUPP). On April 24, 2001, the City Council approved a voluntary annexation of the southwestern 30.3 acres of this site. On March 27, 2001, the City Council approved a Land Use Policy Plan (LUPP) map change for this entire site, which changed the recommended land use from "Residential Low Density" to "Village/Suburban Residential". Zoning. The southwestern portion of the site is currently zoned "A" (Agricultural), which is the zoning that was applied to it when the property was annexed into the City in April 2001. The remainder of the site is currently zoned "RM" (Residential Medium Density) and "RL" (Residential Low Density)with the "RM" zoning located on the northern most portion of the site, adjacent to the "HOC" (Highway Oriented Commercial) zoning of the HyVee shopping center site. Concurrently with this request, the developers have submitted a rezoning request to rezone the site to "RL" (Residential Low Density), "F-S RL" (Suburban Residential Low Density, and "F-S RM" (Suburban Residential Medium Density). Outlots A, B, C, D, and E will be zoned "RL" and transferred to the five existing single-family residential lots adjacent on the west along Jeffery Lane. Lots 8-16, 22-26, and 64-150 will be zoned "F-S RL". The remaining lots, Lots 1-7, 17-21, and 27-63 will be zoned "F-S RM". The proposed single-family attached units that are proposed are consistent with "F-S RL" zoning designation. The T-S RM" zone allows up to 12-unit apartment dwellings. The proposed lot sizes and configurations are consistent with the proposed zoning designations. Utilities. The utilities adjacent to this site will be adequate to serve the needs of this future development. Water Distribution. There are 6-inch water mains existing within: Tripp Street and Coy Street to the east, Dotson Drive and Beedle Drive to the north, and Harris Street to the west. Water mains will be extended into the site from these existing 6-inch water mains. The water mains will be extended to the limits of the subdivision. All costs associated with these water main improvements shall be the responsibility of the developer and will be outlined in the Development Agreement. Sanitary Sewer. There are existing 8-inch sanitary sewer lines within: Tripp Street and Coy Street to the east, Dotson Drive and Beedle Drive to the north, and Harris Street to the west. The sanitary sewer lines will be extended into the subdivision from these existing lines. There will be an 8-inch sanitary sewer main located in the center of all proposed streets. The sanitary sewer mains will be extended to the limits of the subdivision. All costs associated with these sanitary sewer mains shall be the responsibility of the developer and will be outlined in the Development Agreement. Storm Water Management. The project site is currently comprised of agricultural land. Storm water runoff from some of the off-site surrounding residential areas drain into the proposed subdivision. The west edge of the site drains to an existing pond that is approximately one-half acre in size. The drainage from the central portion of this site flows directly into College Creek. The runoff from the eastern portion of the property flows into the adjacent urban area and Franklin Park. Storm sewers ultimately collect this water and route it downstream into the creek. The developed conditions will still receive runoff from off-site sources. However, the existing drainage districts will be significantly consolidated due to the proposed design of the storm sewer system. The City's requirement for storm water management dictate that peak discharge rates of developed conditions cannot exceed those of the existing conditions. For this project site, however, the peak 2 discharge rates of developed conditions must conform to levels below the existing conditions. This is because the proposed drainage of the development utilizes several existing storm sewers. Thus the storm water plan calls for peak discharges that would not exceed the conveyance capacity of the existing adjacent storm sewer system. The storm water management plan will provide storage for storm water generated by the developed site in two detention ponds: one located in the northeast corner of the site and one located on the west side of the site. The detention pond located in the northeast corner of the site will store storm water and route it to the existing storm sewer to the east. The design for the detention in this pond not only meets the existing conditions, but also ensures that the capacity of the existing storm sewer system in the area will not be exceeded. The pond located on the western side of the site will detain storm water before routing it to an existing storm sewer, which flows into College Creek. Again, the peak discharge level will be restricted to below existing conditions so that the storm sewer capacity will not be exceeded. Refer to the attached storm water management plan for additional information. The developers also have submitted a storm water pollution prevention plan for this site, which is located on Sheet 2 of the Preliminary Plat drawing. Electric. This site is in the service areas of the Ames Municipal Electric Utility. The Ames Municipal Electric Utility can adequately serve the site. Street and Vehicular Access. Access to the subject property will be provided from five existing adjacent streets; Tripp Street, Coy Street, Dotson Drive, Beedle Drive, and Harris Street. Tripp Street and Coy Street will be extended to the west through the subdivision. Dotson Drive and Beedle Drive will be extended to the south through the subdivision. Harris Street will be extended to the east through the subdivision. Dotson Drive, Beedle Drive and Cochrane Parkway (located on the south side of the development and providing a future connection to the east and west)will all be constructed as Minor Collector streets (31 feet of paving with parking on one side of the street). All other streets within the development will be constructed as local streets (26 feet of paving with parking on one side of the street). The developers have created a parking prohibition plan for all the streets in the subdivision, which is included in the General Notes for this Preliminary Plat. The traffic study that was conducted for this site indicates that the following improvements are recommended: ■ Construction of left turn lanes on Lincoln Way at the Franklin Avenue intersection for eastbound and westbound traffic; ■ Construction of left turn lanes on Lincoln Way at the Dotson Drive intersection for eastbound and westbound traffic; 3 ■ The Traffic Impact Study indicated that although the Dotson Drive approaches to the intersection appear to fall below acceptable levels of service, it is not recommended that a traffic signal be installed at this location at this time. This location is too close to adjacent signals (particularly Beedle Drive) to operate effectively. It is very likely that as it becomes increasingly difficult for traffic to make a left turn out of Dotson Drive onto Lincoln Way, more drivers will shift their path to Beedle Drive (making use of the existing signal). The City of Ames should monitor this intersection closely as traffic volumes increase. It may become necessary to prohibit left turns from northbound Dotson Drive to westbound Lincoln Way; ■ Paving the unpaved portions of Aplin Road and Dotson Drive; ■ In order to alleviate some of the traffic that may use Franklin Avenue to access the proposed site, the apartment driveway layout should be designed to encourage traffic to use Dotson Drive rather than Franklin Avenue. The addition of a northbound right-turn lane at the Lincoln Way/Dotson Drive intersection may also help in this matter. While the traffic report indicates that a traffic signal is not needed at the intersection of Lincoln Way and Beedle Drive at this time (due to the adjacency to existing signals), staff believes that the traffic counts for that intersection warrant the installation of a traffic signal at this time (see attached memo from Public Works Department). The traffic counts as indicated in the traffic study are significant enough to warrant the installation of a traffic signal at this intersection with the development of the subject site. Even though this intersection is in close proximity to the Beedle Drive/Lincoln Way intersection, which already has a traffic signal, the location is not too close for the installation of another signal. The traffic signals at the two intersections would be coordinated (timed) so that they would operate effectively together. The details regarding timing and responsibility for installation of this traffic signal will be documented in the Development Agreement for this subdivision prior to the Preliminary Plat for South Fork Subdivision being placed on the City Council agenda for action. The traffic study indicates that the unpaved section of Aplin Road and Dotson Drive should be paved. The section of unpaved Dotson Drive is adjacent to the subject site. The unpaved section of Aplin Road is not adjacent to the subject site. It is City policy that the developer pay 50% of the cost of paving the section of Dotson Drive that is adjacent to this development. The remaining 50% would be paid through an assessment to the surrounding property owners. All of the cost of paving the unpaved section of Aplin Road would be covered by an assessment to the surrounding property owners. Given City policies and past City practices, this is most likely the assessment scenario that would take place for the paving of these sections of streets. However, all assessments must be reviewed and approved by the City Council. Details regarding the paving will be documented in the Development Agreement for this subdivision prior to the Preliminary Plat for South Fork Subdivision being placed on the City Council agenda for action. 4 Since all of the recommended improvements are off-site improvements, there is nothing to illustrate on the proposed preliminary plat drawings. The street improvements and intersection improvements will have to be documented in the Development Agreement for this subdivision prior to the Preliminary Plat for South Fork Subdivision being placed on the City Council agenda for action. Staff has reviewed all the street names for this subdivision, all of which are acceptable names. Sidewalks will be constructed on both sides of all the public streets. Also, mid-block pedestrian walkway easements are shown where block lengths exceed 660 feet in length as required by the Suburban Residential regulations. A bicycle path is located on the east side of the development, extending from Tripp Street to Franklin Park. A bicycle path will be located within the greenbelt easement along College Creek. These bicycle paths will provide access for residents throughout the subdivision and are consistent with the Bicycle Master Plan. Construction of the sidewalks and bicycle paths is the responsibility of the developer and will be documented in the Development Agreement. Landscaping. A street tree planting plan is required for all streets within this subdivision since all these streets are residential streets. The developers have indicated that they intend to plant street trees within the right-of-way of all streets in accordance with the tree species and spacing requirements of the City. Specific street tree planting plans shall be submitted with the Final Plat for each phase of this subdivision. Installation of the required trees will be processed as building permits are issued for dwellings within the subdivision. STAFF COMMENTS: Staff believes that this Preliminary Plat can be approved subject to the following stipulations: 1. That a Development Agreement shall be prepared and signed by the developers prior to the Preliminary Plat for South Fork Subdivision being placed on the City Council agenda for action. This agreement shall document the developers' and the City's responsibilities and costs associated with the development of the South Fork Subdivision. 2. That the approval of the Preliminary Plat shall not become effective until the rezoning of this property to "RU, "F-S RL" and "F-S RM" is completed. 3. That the developer shall be responsible for the cost of constructing left turn lanes on Lincoln Way at the Franklin Avenue and Dotson Drive. Such responsibility shall be documented in the Development Agreement. 4. That the developer shall be responsible for the cost of installing a traffic signal at the intersection of Lincoln Way and Dotson Drive. Such responsibility shall be documented in the Development Agreement. 5 5. That the developer shall be responsible for 50% of the cost of paving the unpaved portion of Dotson Drive. Such responsibility shall be documented in the Development Agreement. 6. That a street tree planting plan shall be submitted with the Final Plat for each phase of this subdivision. 7. That the developer consolidate Outlot F into Mr. Cochrane's property to the west prior to the approval of the Final Plat for the phase which contains Outlot F. RECOMMENDATION OF THE PLANNING & ZONING COMMISSION: The Planning and Zoning Commission reviewed this request at their meeting of July 18, 2001 and approval was recommended with the following stipulations: 1. That a Development Agreement shall be prepared and signed by the developers prior to the Preliminary Plat for South Fork Subdivision being placed on the City Council agenda for action. This agreement shall document the developers' and the City's responsibilities and costs associated with the development of the South Fork Subdivision. 2. That the approval of the Preliminary Plat shall not become effective until the rezoning of this property to "RU, "F-S RU and "F-S RM" is completed. 3. That the developer shall be responsible for the cost of constructing left turn lanes on Lincoln Way at the Franklin Avenue and Dotson Drive. Such responsibility shall be documented in the Development Agreement. 4. That the developer shall be responsible for the cost of installing a traffic signal at the intersection of Lincoln Way and Dotson Drive. Such responsibility shall be documented in the Development Agreement. 5. That the developer shall be responsible for 50% of the cost of paving the unpaved portion of Dotson Drive. Such responsibility shall be documented in the Development Agreement. 6. That a street tree planting plan shall be submitted with the Final Plat for each phase of this subdivision. 7. That the developer consolidate Outlot F into Mr. Cochrane's property to the west prior to the approval of the Final Plat for the phase which contains Outlot F. 6 ALTERNATIVES: 1. Recommend that the Preliminary Plat for South Fork Subdivision be approved with the seven (7)stipulations listed above as recommended by the Planning and Zoning Commission. 2. Recommend that the Preliminary Plat for South Fork Subdivision be denied. 3. Recommend that the Preliminary Plat for South Fork Subdivision be approved with modifications. 4. Action on this request can be postponed and referred back to City staff and/or the applicant for additional information. RECOMMENDED ACTION: The proposed development of the South Fork Subdivision is consistent with the goals and policies of the Land Use Policy Plan. The subject area is undeveloped and highlighted as an area that is preferred for residential growth. The staff believes that the Preliminary Plat represents the most effective method of developing in this area of the city. It is recommended that Alternative #1 be adopted. Alternative #1 is an approval of the Preliminary Plat for the South Fork Subdivision with the seven (7) stipulations as recommended by the staff. 7 • Memo Public Works Departrr Caring Peo Quality Progr Exceptional Se e TO: Planning and Zoning Commission Members FROM: Scott Logan, City Traffic Engineer DATE: July 13, 2001 SUBJECT: Traffic Impact Report for the South Fork Subdivision During the review of the South Fork Subdivision, staff has indicated to developers that the Traffic Impact Study Recommendations for this subdivision were acceptable except for the one concerning traffic signal controls at the Dotson Drive/Lincoln Way intersection. The study recommendations state that although the Dotson Drive approaches to the intersection appear to fall below acceptable levels of service, it is not recommended that a traffic signal be installed at this location at this time. The consultant further indicates that this location is too close to adjacent signals (particularly Beedle Drive) to operate effectively. It is also noted in the report that it would be very likely that as it becomes increasingly difficult for traffic to make a left turn out of Dotson Drive onto Lincoln Way, more drivers will shift their path to Beedle Drive (making use of the existing signal). The consultant recommends that the City of Ames monitor this intersection closely as traffic volumes increase, and it may become necessary to prohibit left turns from northbound Dotson Drive to westbound Lincoln Way. Staff does not concur with this recommendation since it is believed that the benefits of installing a traffic signal at the Dotson/Lincoln Way intersection for traffic safety purposes greatly outweighs the negatives concerning traffic flow interruptions along Lincoln Way. Staff believes that a traffic signal should be installed to provide safe "gaps" in the Lincoln Way traffic stream for motorists egressing from the Dotson Drive approach. Without these safe gaps, a significant number of right-turn and left-turning type of accidents will occur at the intersection as traffic increases. It should be noted that the projected volumes at this location will meet traffic signal warrants based on the Federal Highway M r A N - � L W p. ee� .es tl. E 0 4. Z J 0 r wo- am I 3 w 0 Y 00TRIPPT d AP IN RD SN Twocc- a g e- arr ily Famil �' w F ingl Fam co g Zw' J Z c CID J � w rn t d T' to Fa r in I F m ly F it 1 � f � Pr�oposetl ���� Existing Land Uses N w E S Prepared by the Department of Planning and Housing 200 0 200 400 Feet Map prepared:0710512001 Fm is x + catiort� I � as _ &Holding City ParK Pond LL J Z `Y w wo- am ly 3 LLI IF IPP T APLIN RD o Two- Famil F l LL g a ily � �utFa it uingl -Fam a F (a g LL � J_ Z F _ S n le- a ily G i t a i d N C2 J LL in - N w N inLL le T i I a iyA c d F� in le- 'i R Si gl Fa ly -T in I F m ly F it � in cca cc d d �a S ngI La rOVqT F mi y Si ngl F it Sin le �l Fa it AOW.- �Pontl A eeK in le- am ly e C,r � ;3 p x �r d', j .� y ae' SrihoO a71t�., P '`ems WHO! "77,777 zA a _ Proposed Land Uses N W E S Prepared by the Department of Planning and Housing 200 0 200 400 Feet Map prepared:0710512001 S�\NG �N HOC H HOC HOC F7- S-GA cr W RM J W W m TRIPP T APLIN RD cl RL C LLLJ g Z cc W U- lL US ST A RL t z —.j R4 I A S-GA Existing Zoning N W E S Prepared by the Department of Planning and Housing 200 0 200 400 Feet Map prepared:0710512001 LN s. \NG HOC 6H HOC HOC S-GA 0 F -R w w 00TRIPEST APLIN RD (n RL FS-RIV Z J } w LL IIS LL R F - L S-GA Ir7�� Proposed Zoning N W E S Prepared by the Department of Planning and Housing 200 0 200 400 Feet Map prepared:0710512001 wA�r Highway-Or nted Commercial 4 s Low-Density Resic 0 2 �. W Z J 0 ` \ W � =�� r `S T b 1"CO O 3TRIPP, T APUN R� Uillage/Suburban esider t�al "' = , Y o R-Desty R si enti I k 4 }.# z _j 3 a� Ll z e ` av� LL U. } \ r z c z �� Uillage/Suburbgan ResidentiaLL *ti ,'� e l� r Low-Dens ity Residential w Land Use Policy Plan N W E S Prepared by the Department of Planning and Housing 200 0 200 400 Feet Map prepared:0710512001 iRP u� y � �' k 5:es¢aa uses¢ s r I �• (/) < R�KINHet I . �• r4nrsiMW s__-_. IO I R�, ., j .D a �,I .- rtt 3-( n � LC����dv �•d �OWN� J'; -;II& (D �: I yin o A Z gs 9 r rr- R1 rr M CD o s ZZ — b D D Z mi 6 N d a Z MR 00 I r dt (D CID �4���'� � �� H - � � ' - I_ qI N- - �SYJt1IGQ=RBXy XXYCItYX'JY'SYYYhtl YYii�isiuv•as.+err.�u..- z z ���� / f � .og'. � I � �yI N. . � � gaaeXaXaneSaa�talaa:ed.�yx.It�wyKSSSSSLStc SS.SSiea: (D z T N I �I...°� A `Y ;3�3 SEESE�S�92iF�aQg9S9PSP9aegaa�Ysiae■R31Sgg�Sl4 CD cl 00 o CDpg rF 1 1 I �gt$g I. e � _ oll V ` 4 x J3t 3L P e r telltD . ygj Illppnnn y I age EE77 Iby MY ny Cb I M I - ,14 I I I r N cL \a g N I I XI I a cn IT x I , N I 1 m• ,� L e ururt' M&EW mlCz 'a —.+ — n o u n 7C-0O PA~ — -- - 2I/ it>o - _+�_ _ b"r��. is-... ._A3_ — as —sib ays*`— 'e.._ wl CD Srtr'� m ' m 'a w n - nOWL \ _ c I " 5 I I A s. PRELIMINARY PLAT - North EnglMw. eee► Pl..— South Fork Subdivision �an°g°eZ= Owner: Terra Firma L. P.,207 Stanton Avenue,Ames, IA 50014 ENGINEERING PLUS, INC. Amas,low. S1 S232-g553 PA%315233-5976 AafnxSopllm Iblll'R RLV•N N.r 1 xn n[[ [tY A-n. -' • I(n+Fn 1�. rYtf[I'[ :,' /.y. �,' �_. .,�'/ ... ..I•_-. ..'.l. LLI[[A CPS LMMIG➢.L �nRil¢,PM A6MY I � .NL 1M- • A. Y s 16 oo __ „ w_ Go / a / el OL AN r s 3 I I I N-W IRA N o Al ors. Af • M I B _ ra - - g6 a RLRf a uE 6 un _ a I : MA 'S072739•E 666.22 7n t YI r s Iv 8 aI yx . I II to •�� UHU !t HIM �jff E�Q YSSDsa > S�ggxSF y d� 4 �d•!�91 1i •9s� 9��• - - S S s 9�� sg 6AY 1 g - i<A•g l� �. a -rwIla if ! lit g Ili I ;K I i f lit Sin �� ��� € � � � s� � � '� s� � ��������';f � p I -- °•'-- I � ; / Slit '['� '-j _ susitg :� { { I ► 1= pi 14 Id" - -- I �1i4 � �•� � 2�� ��$ b� �d'� � g^ � ��� i�Ma�� �,��� Al gQ. I �i nT co $I ,n $ Q I a a �AIFJIW N p QJMIAYVI -!u $I t0 I c I$ -0 11< C j gn 4'7 J I SY a 11CI!!11Q1' . $ a r NORTH e $ Ya c N — $ 8 I :i IlLwum tT p PRELIMINARY PLAT - South e Englnfan Plan— N A South Fork Subdivision Land S—ym Land-dap.AYYYI.saf Owner: Terra Firma L. P.,207 Stanton Avenue,Ames,IA 50014 ENGINEERING PLUS, INC. Ame>Ian Sti232d5S3 FAX 515233-5976 Preliminary Storm Water Management Report For South Fork Subdivision In Ames, Iowa July 2001 Prepared by Ismael Martinez, P.E. Bonestroo Rosene Anderlik and Associates 2335 West Highway 36 St. Paul, Minnesota 55113 E,VCD (651) 636-4600 0 2001 CITY OF AMES,IOWA DW OF PLANNING& OU&ING South Fork Subdivision Storm Water Report Proiect Summary The proposed South Fork subdivision is situated in the west portion of Ames, Iowa. The project site is located south of Lincoln Way, north of College Creek and west of Franklin Park (see Figure I). College Creek, which drains this parcel, flows below the project site and discharges into a pond in the Iowa State University campus. The surrounding immediate land use is low density residential housing and agricultural fields. The development is proposing to establish primarily low and medium density housing with the remainder as high density, multi-family complexes. The proposed site is 56 acres, almost half of which will be comprised of single family detached lots. The City of Ames requires that storm water flow levels do not exceed those for the pre- development conditions. The software program Hydrocad was used to model the existing and anticipated conditions after development. Storm events of 5, 10, 50 and 100 years were modeled to gauge peak flows. Rainfall amounts (in inches) used for these 24 hour events were 3.6, 4.3, 5.9 and 6.6, respectively, based on SCS data. Existing Conditions The project site is currently comprised of agricultural land. Open fields dominate with woody vegetation on the edges. Some of the off-site surrounding residential areas drain into the proposed subdivision. The west edge of the site drains to an existing pond that is approximately one-half acre in size. The drainage on the central portion of this site flows directly into College Creek. The runoff from the eastern portion of the property flows into the adjacent urban area and Franklin Park. Storm sewers ultimately collect this water and route it downstream into the creek. Existing levels of discharge were evaluated based on both on-site and off-site sources. Table A and Figure 2 show discharges for the existing drainage districts Table A -Exis ing conditions Drainage CN Land Use Area Peak Peak Peak Peak District (acres) Discharge Discharge Discharge Discharge (5 ) 00 ) (50 ) (100 ) Al 71 A-riculture- 20 21.2 29.3 53.7 64.9 B 1 40 Agriculture 6.4 0.0 0.1 0.8 1.5 (depression) C5A (off-site) 77 Residential 6.4 12.5 16.3 27.1 32.0 C513 76 Agriculture 12.2 17.3 22.4 38.6 45.8 D 1 A (off-site) 82 Residential 1.8 4.4 5.5 8.7 10.1 D1B 72 Agriculture/ 4.8 7.2 9.8 17.4 20.9 Wetland EI 66 Steep slope 0.5 0.5 0.7 1.5 1.8 F I 66 Steep sloe 6.4 5.6 8.2 16.1 19.9 G 1 66 Steep sloe 1.4 1.4 2.1 4.1 5.0 H 1 66 Steep sloe 2.8 2.8 4.2 8.1 10.0 J I,J2,J3,J4 92 Commercial 5.2 17.8 21.2 30.3 34.3 (off-site) Developed Conditions The developed conditions will still receive runoff from off-site sources. However, the existing drainage districts will be significantly consolidated due to the proposed design of the storm sewer system. The storm sewer pipe sizing utilizes a combination of diameters in order to most effectively convey drainage and minimize overflow in areas of varying topography. In Ames, Iowa, peak discharge rates of developed conditions are not to exceed those of the existing conditions. For this project site, however, the peak discharge rates of developed conditions must conform to levels below the existing conditions. This is because the proposed drainage of the development utilizes several existing storm sewers. Thus the storm water plan called for peak discharges that would not exceed the conveyance capacity of the existing adjacent system. Peak discharge rates were calculated and the results are in the Table B. Table B—Developed Conditions (No Pondin Drainage CN Land Use Area Peak Peak Peak Peak District (acres) Discharge Discharge Discharge Discharge (5 ) (10 ) (50 ) (100 ) A 89 Residential 27.4 72 90.5 132.7 151.1 - - (J 1,J2,J3,J4,and art ofBI) C 79 Residential 32.5 57.6 77.8 126.3 147.9 (C5A,C5B, D t A, D 1 B,portions of Bl, El, F1) F 69 Residential 3.7 4.3 6.5 12.1 14.7 G 87 Agriculture/ 2 5.7 7.2 10.7 12.3 Wetland G' 75 Residential .5 0.8 1.2 2.0 2.4 H 78 Steep slope 1.6 3.1 4.3 7.0 8.2 Storm Water Management StrateU Two storm water detention cells will be required to control water quality and quantity for the proposed development. Modeling of water quality conditions was performed using PondNET. Model parameters were taken from Bonestroo Rosene Anderlik & Associates' Surface Water Management Plan for Halletts Quarry Lake Watershed (April, 2000). Table C provides details for pond sizing and performance. These numbers may change with final design. Peak discharge from both ponds was limited by the existing storm sewers. Figure 3 shows anticipated discharges for the developed project site after ponds are created. Table C— Pond Desi n NWL HWL Mean Wet Storage Phosphorous Peak Depth Volume Capacity Outflow Discharge (Ft.) (Ac. Ft.) (Ac. Ft.) ( b) (100 yr) Pond 1 165 172 4.0 4.0 4.8 200 31.9 (Q 1) 20.9 (Q2) Pond 2 170 175 4.0 3.4 1 2.85 194 63.1 The upstream pond (Pond 1) will serve drainage district A, receiving a peak flow input from a 100 year event of 151 cfs as shown in Table B. Districts J 1, J2, J3, and J4 drain into an existing storm sewer which is currently routed to Tripp Street and downstream to the east. This development proposes to route flow from these four parcels into Pond 1 in order to alleviate conveyance capacity demand on this existing storm sewer. Ultimately this allows for higher peak discharge from the pond. The control structure for this pond will have a staged design, allowing for minimum discharge during low flow periods. Further, an engineered sag in an adjacent bike path will serve as an overland flow point. Pond I is designed to contain events on the order of magnitude of a 50 year storm. Larger magnitude events will flow from this overland outlet into the adjacent Franklin Park. This design ensures that the capacity of the existing storm sewer structure will not be exceeded. For a 100 year event, the peak discharge to Franklin Park is approximately 21 cfs, below the discharge for the existing conditions. Peak discharge to the storm sewer is approximately 32 cfs. Above the 100 year storm event, any emergency overland flow will spill from the southeast corner of the pond into Tripp Street. It will flow to the east and will collect in low areas of the street directly adjacent to the project site. Pond 1 will perform water quality treatment prior to discharge. Treatment efficiency will be improved by the use of a berm which will prevent incoming water from directly flowing to the outlet. This will increase the hydraulic residence time of the pond, allowing sediments and phosphorous to settle out. With a wet volume of 4 acre-feet and mean depth of 4 feet, modeling estimations show that the pond will remove 65 % of total phosphorous, with a discharge concentration of 200 ppb. Pond 2, situated downstream in the southwestern portion of the project site, will also have a staged outlet structure to keep low flow discharges to a minimum. The pond will serve the drainage district C. Table B shows the peak flow input from a 100 year event is 148 cfs. One option for the design of this pond involved using the existing, off-site pond as a second cell for storm water treatment. This alternative was not pursued due to the extensive amount of berming that would be required to meet the necessary storage volume. Instead, the pond design will utilize the existing wetland to help route the runoff and improve the water quality. Discharge from Pond 2 will be routed to an existing storm sewer which flows to the creek. Here again, the peak discharge level was restricted to below existing conditions so that the storm sewer capacity was not exceeded. For a 100 year event, peak discharge to the storm sewer is approximately 63 cfs. With a wet volume of 3.4 acre-feet and mean depth of 4 feet, modeling estimations show that the pond will remove 67 % of total phosphorous, with a discharge concentration of 194 ppb. The remaining proposed districts are not routed to detention ponds. Existing drainage District G 1 becomes divided into two districts, G and G' based on new roads from the development. Runoff from district G is captured by storm sewers which convey flow to the east away from the project site. Districts G' and H drain via backlot flow; H flows south to College Creek and G' to off-site lots. 2"x8" keyway cast into wall by supplier 3.0' 3.0' Baffle wall A 3.0' constructed in field by 1.0' contractor J_^. ._. _ I_I _ _. I-_._I i _ Weir opening Weir opening _ _ in baffle wall _____ — in baffle wall Skimmer - - ..I Elev.= 165.0 R---�--additional #4'S opening � I x 4'-0" long See Plate 1 -35 _ _._ _ ___i- #4 ® 12" For grate A t horizontal ;- design see Plate 1 -35 Hole for = 1131.5 21 " RCP #4 0 12" SKIMMER vertical GRATE SECTION A—A CONCRETE BAFFLE WALL NOTE: Weir opening in Baffle wall height 8" baffle wall ±is greater than 3' above 1 NWL; the following shall Elev.=171 .0 be required: Elev.=171 .0 � T 1• Steps 2. 6' Diameter MH Elev.=168.3 Hole for 21 " Dia. NWL Elev.=165.0 outlet pipe 1' 5' X 1.5 min. opening Elev_=163.0 see Plate 1 —35 6" 7 6' Min. 1 ' 8 CY Class o � 8" Min. slab 3 Riprap U06,• thickness 00 OO 6' Dia. typ. manhole 6" aggregate backfill (MnDOT Spec. 31491-1 Mod.) Last Revision: ©� Bonestroo OUTLET DETAIL June 2001 ibsena BRA Plate No. Ander/ik& SKIMMER STRUCTURE WITH Associates CONCRETE BAFFLE WALL 1 -36 Enghwors 4 A/Oh/roOli (DRAWING NOT TO SCALE) Project # M. Pain MlnrweoJo [666-01-10,)2 Provide 6-1/2" SS anchor bolts w/clips 1 1/2"x3/8" outer ring 1 1/2"x3/8" steel bars ® 4" O.C. SKIMMER 1 -1/4" MH DIAMETER OPENING / I � 4' 3'x 1.5' I 6' 6'x1.5 Provide 1/4" plate with locking clasp Clasp to have 1/2" padlock hole 1/4"x1/4" steel bar, weld to each member Hot—dipped galvanized grate in 2 sections Provide 1/2" Dia. Continuous Hinge Bar GRATE DETAIL 1' Elev.=xxx.x NWL Elev.=xxx.x Hole for xx" Dia. RCP 1 ' Skimmer opening 1 1 .5' 6" Min. 8 CY Class t 00 g" Min. slab 3 Riprap g�� thickness 00 Dia. Varies 6" aggregate backfill manhole (MnDOT Spec. 3149H Mod.) Last Revision: m Bonest�oo June 2001 tom Absene STANDARD SKIMMER DETAILS BRA Plate No. Andar/ik& Associates STANDARD SKIMMER STRUCTURE 1 —35 Enolnodpia A Arch/leclr (DRAWING NOT TO SCALE) Project # st.veut M/nnerat, 666-01 -102 o oa In L .Co 4 N _ ° N � 0 L:, � °� � i3-� ' -- • - ��� R LL Q; i I Q p w cv Z _ OL ti a i 1 �- 1 '^ to f p • l LIJ o w co w Q (n U Y � Q O WW � d V) F1 Z O o W V) � N O / O m V O � � V) g/ Y U O o Li CIOQ O LL- 0 — 0 O cn ►— / w is J1 a- a M 1� ri MEMO loll IWO PER VAN ME IMPEORM gm Fit OX ���►.'�� �tr` ll� .� , . ,,,, NOW F III ME� vrt��!StC4�� • { I d5 vi 00 a`v+ LA It n I N 1 I O O Q Q CA JLjj 1,.. I N�� 1• it �' �;..y 46, >✓ti 1,. .; �i — V; 1` �J"-`�^''1-- c i cj lw 1 r. • rli ' R � j _ �1 Ul I a