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8b. Wetland permit for sedimentation basin adjacent to a class B wetland PC DATE: 12/2/92 '-� ' (, C1TY OF ��% CC DATE: 12/14/92 \ '� �1 1 C HANII�SSEN 1 r CASE #: 92 -11 WAP �� By: Aanenson:• 111 1 STAFF REPORT 1 PROPOSAL: Wetland Alteration Permit for a Sedimentation Pond adjacent to a Class B 1 Wetland Z LOCATION: North of West 78th Street between Kerber and Powers Boulevard I V APPLICANT: Brad Johnson 1 Lotus Realty P.O. Box 235 Chanhassen, MN 55317 II Q I Act t CTty Ac•nlrr tot 1 PRESENT ZONING: R12, High Density Residential : ,- ,, DWIA 1 ACREAGE: 2.25 acres r . i Y - ' r ..:1 _12 ) t - D DENSITY: I ADJACENT ZONING AND � h� LAND USE: N - RSF; Residential Single Family ___ I-2---147 _ I S - BG General Business Q E - PUD, Planned Unit Development Residential and OI, Office 1-- Institutional 1 Q W -R12, High Density Residential W WATER AND SEWER: Not applicable I PHYSICAL CHARACTER.: The site is a ravine that was altered to create two sedimentation (n ponds with the development of the Saddlebrook subdivision. This 1 is a Class B wetland and has an Ag/Urban and Natural classification under the city proposed wetland ordinance. 1 2000 LAND USE PLAN: High Density Residential 1 1 Oak Ponds /Oak Hill WAP December 2, 1992 1 Page 2 PROPOSAL /SUMMARY The Oak Ponds /Oak Hill development is a 217 unit multi - family housing project on a 27 acre site located between Powers and Kerber Boulevard. This project received preliminary, site plan ' and PUD approval by the Planning Commission on November 4, 1992. One of the conditions of approval was that this project receive a wetland alteration permit. 1 ANALYSIS The applicant has contracted with Bonestroo,Rosene, Anderlik and Associates to perform a storm water and water quality review for the proposed "Oaks" development. There is an existing Class B wetland that is located in the northern portion of the proposed Oak Ponds Development. This wetland was altered in 1987 with the development of the Saddlebrook Subdivision. With the development of the Saddlebrook Subdivision, two storm water retention ponds were created. These ponds straddle the proposed Oak Ponds and the Saddlebrook development. Although this area is one basin, there are two distinct areas of wetland; one is the Class B wetland along Powers Boulevard and the other area includes the two pretreatment ponds along Kerber B oulevard. This site was inspected as part of the wetland inventory the city undertook as a part of the Surface Water Management Program. The most westerly pond, the Class B wetland, was noted on the inventory as a possible Natural Wetland and the two ponds to the east along Kerber 1 Boulevard were noted as Ag \Urban ponds. The direction the city is heading with the wetland classification is that Ag \Urban wetlands may be allowed to be modified but not those classified as Natural. The DNR and the Army Corps of Engineers have stated that they have no 1 jurisdiction in this wetland. The drainage plan for this project is divided into 11 areas, A to H area A -1, B -1 south and B -1 east. While drainage areas C, D, E, and G drain directly to the wetland, area A. A -1, B and B -1 drain to the east pond and F and H drain to the existing west pond. Ismael Martinez, from Bonestroo, is recommending the following improvements for storm water management: • Enhance the quality of the existing Class B wetland. 1 Modification of the two existing ponds to better accommodate runoff generated by the proposed development. 1 Modi fication of the internal drainage to keep runoff within the proposed development. • • Provide a sediment trap to the proposed storm water before discharging in the existing wetland. 1 1 1 Oak Ponds /Oak Hill WAP 1 December 2, 1992 Page 3 I • Define the Normal Water Level (NWL) for the wetland and provide the proper outlet. • Develop an off -site NURP basin with a developer's contribution to the Surface Water 1 Management Program Fund. Specifically the proposed storm water management consists of the following: 1 Eastern Storm Water Pond I Construction of a 20 foot long, broad crested weir at elevation 955.0 to provide protection against overtopping. 1 The outlet structure should consist of a 12 inch diameter pipe discharging into the west pond partially submerged to avoid erosion. 1 Westerly Storm Water Pond Construction of a 20 foot long, broad crested weir at elevation 949.0 is being proposed by Ismael I Martinez. This weir, which will help define the overflow, will need a 20 foot wide energy dissipator with its bottom 10 inches below the wetland ground elevation and designed to maintain sheet flow for at least 10 feet (riprap protection). The outlet structure should consist of a 15 inch diameter pipe discharging into the energy dissipator. The benefit of this weir will aid in reducing the flooding potential of the ponds. 1 Ismael Martinez states that both weirs can be built by cutting a well defined section in the existing berms. The side slopes for the weirs are recommended at a 5:1 for maintenance 1 purposes. Both weirs, their discharge section and the energy dissipator should be protected with riprap. The soil removed to build the weir section can be spread on top of the corresponding 1 berm which would add free boards to the pond for protection against overtopping. 1 The final parameters would then be: I East Pond West Pond Normal Water Level (NWL) 953.9 948.1 High Water Level (HWL) 956.0 950.0 Discharge cfs 52.0 73.0 Storage Volume AF 1.2 1.1 Outlets: I 20' crest weir elevation 955.0 949.0 12" Pipe 953.9 15" 948.1 1 1 1 Oak Ponds /Oak Hill WAP December 2, 1992 ' Page 4 The storm sewer for areas C, D and E should not discharge directly into the existing culvert under Powers Boulevard. Instead Ismael Martinez is recommending that a sediment trap be created before discharging into the wetland. A sediment trap with a sedimentation capacity of 3000 cubic feet and a minimum depth of three feet is recommended. This trap should provide sediment removal without significantly impacting the surroundings. The sedimentation trap shall be located outside of the wetland boundary, and east of the proposed bike trail along Powers Boulevard. Ismael Martinez has stated that the Class B wetland shows signs of erosion in the middle of it. Runoff has eroded a small meandering channel in the middle of the wetland. With this new development, the amount of runoff will ' be increased and with it the amount of erosion. He is recommending defining a Normal Water Level (NWL) and High Water Level (HWL) for the wetland and provide a proper outlet structure to control storm runoff. In addition, he is recommending the city consider a cash contribution ' from the developer to the Surface Water Management Program to address water quality issues downstream. ' The Natural wetland is a part of the overall drainage system and will meet 100 year storm design criteria. A pond to meet NURP standards can not be developed on this site because of the constraints of the natural topography and the steep slopes. This is an instance where the city should require a contribution to the storm water management program. This contribution would aid in the acquisition or improvement of ponding facilities. In this instance, the downstream pond on the Eckankar property will be designed to NURP standards. The Surface Water ' Management Program Task Force will have to review the formula being used to determine this cash contribution. Currently, this contribution is being based on land value. 1 SUMMARY The proposed construction of the sedimentation pond will be adjacent to the Class B wetland 1 along Powers Boulevard. No activity will occur within the wetland boundaries. Currently, the city's wetland ordinance allows a sediment basin within 200 feet of a Class B wetland without a Wetland Alteration Permit. The other two retention ponds will be modified only at the ' discharge points. This modification consists of the construction of a long crested weir and outlet structure. The modifications to the existing storm water ponds will result in an overall 1 enhancement of the Class B wetland by regulating storm water discharge. PLANNING COMMISSION G CO SION UPDATE S On Wednesday December 2, 1992, the Planning Commission recommended approval of the wetland alternation permit. The residents in attendance were concerned about the modifications to the existing storm water ponds as these ponds have had a history of overflowing. If was explained by staff that these modifications would improve the function of the ponds and direct overflow to the Class B wetland. 1 1 1 Oak Ponds /Oak Hill WAP 1 December 2, 1992 Page 5 ' RECOMMENDATION Staff recommends the City Council adopt the following motion: "The City Council approves Wetland Alteration Permit #92 -11 with the following conditions: 1 1. The limits of the sedimentation trap shall be limited to the 944.0 contour adjacent to the Class B wetland. 2. The existing two storm water ponds shall be limited to modifications as proposed including the weir and outlet structures. 3. Type III erosion control be in place around the construction boundaries of the wetland. 1 4. A cash contribution to the Surface Water Management Program Fund, as determined by the city." ATTACHMENTS 1. Letter from Ismael Martinez dated November 18, 1992. 2. City of Chanhassen Wetland Observation Records, dated May 13, 1992. 3. Letter from DNR dated October 2, 1992. 1 4. Letter from the Army Corps of Engineers dated October 30, 1992. 5. Planning Commission minutes dated December 2, 1992. 1 1 1 1 1 1 1 Otto G. Yor+emon PE. *owed A, Sambre, PE, Michael P. Rau. PE. Mlles B Jensen. PE Bonestroo Rosen RROWi W Rose*, PE' Roth A. OOdors, P1 Apses M. Ring. , A,ItP L R'twlup Graver tll, P.ti Bonestroo ` V �meph C, Anderllk, P.E. Robert R. Pfeffer* . PE. Thomas W. Peterson, PE Karen L. WIerne, 1J p Marvin L. Sava*. PE. *hard W. sower, PE, WWI C. lynch. PE. Gary 4 KrlstWih, PE Richard E TWfkr, P , Dauld 0 Loskota, PE James R. M.{and. PE F. Todd Poster. PE A nderiik & Thomas E No PE Jerry A BR s ti, PE. J D P Ar erWn, Pi. Shawn D M PE. PE. Associates Robert G Sc t. PE Mark A, Manson. P.E. Mark R. Relit P.E Ceedro Oehler. PE. Susan M. Eberlinerun, P,/1 C , Michael T. Rauvnann, PE. Mark A. Sip PE Charles A Erickson "Senior Consultant Ted K Fkk7. PE. Gary W. Morten, PE, Leo M Pawelsky Engineers b Architects Thomas R. Anderson. A 1 A. Darnel J. EdgsrtorL P.E. Marlin M Won g Donald C. Sugar , PE. Daryl K Kfrscnenman, Pk. James r. Engelhardt Thomas E. Angus P.E, PNYp J Caswell, PE. Nmael Martinez PE Mark D Walls. P.C. 1 ' MEMORANDUM TO: Kathryn Aanenson, City of Chanhassen Fax No. 937 -5739 FROM: Ismael Martinez �, ' DATE: November 18, 1992 RE: Oaks Community Plat Review ' FILE NO.: 393Gen ' Hi Kate ' INTRODUCTION We have performed a stormwater and water quality review of the proposed development, Oaks Community Development. Our review was based on the proposed development characteristics shown in the Plat plans dated October 6 and received by the City October 7, 1992. As a result of our review we recommend the following improvements: - Modification of the two existing ponds to better accommodate runoff generated by the proposed development. - Modification of the internal drainage to keep runoff within the proposed development. - Provide a sediment trap to the proposed stormsewer servicing areas C, D & E, before 1 discharging into the existing wetland. • Define the Normal Water Level NWL for the wetland and provide the proper outlet structure. OBSERVATIONS The proposed development is located East of Powers Blvd and North of Arboretum Blvd, in the SW 1/4 of the SE 1/4 of Section 11, T 116 N, R 23 W, in the City of Chanhassen. 2335 West Highway 36 • St, Paul, Minnesota 55113 • 6124364600 z ©' d •OSSd 2 002:11.93N09 TUT 929 !T9 917 :VT E66T -9T -TT 1 The proposed development drains naturally to two existing man -made ponds and a natural B wetland. For the purpose of this review the two ponds will be called East and West accordingly. The wetland is classified as a Palustrine, with Emergent Vegetation and Seasonally Flooded waterbody in the National Wetland Inventory. The drainage system shown in sheet 3 follows the natural topography and has been divided into 11 drainage areas, A to H including areas A -1, B- 1 south and B -1 east. While drainage areas C,D,E and G drain directly to the wetland, areas A, Al, B and B1 drain to the east pond and area F & H drain to the existing west pond. , The two existing ponds were originally designed to control runoff from Saddlebrook development located north of the Oaks. ' The proposed development site has a very well defined natural topography and steep slopes near the existing ponds. RESULTS We reviewed the capacity of the existing ponds to control runoff generated by the proposed ' development. The ponds will have to be either enlarged or their outlets would have to be modified. If ndin would be required to treat and control runoff ' Po 8 �l re off generated by the proposed development, the east and west ponds would have to be expanded .5 and .2 acres respectively. Potential areas to expand the existing ponds are heavily wooded and are characterized by steep slopes. We evaluate the alternative of not increasing the pond capacities and its impact to downstream ' waterbodies. We recommend the modification of the two existing ponds to better accommodate runoff generated by the proposed development. The modification will consist of: 1 East Pond * Construction of a 20' long, broad crested weir at elevation 955.0 to provide protection ' against overtopping. * Outlet structure should consist of a 12 inch pipe discharging into the west pond partially submerged to avoid erosion. ' West Pond * Construction of a 20' long, broad crested weir at elevation 949.0. The weir will need a 20' ' wide energy dissipator with its bottom 10" below the wetland ground elevation designed to maintain sheet flow for at least 10 feet ( riprap protection). * Outlet structure should consist of a . .ipe discharging into the energy dissipator. ' i Both weirs can be built by cutting a well define section in the existing berms. The side slopes for the weirs are recommended at 5 :1 for maintenance purposes. Both weirs, their discharge section and the energy dissipator should be protected with riprap. The soil removed to build de £0'd '3S2t OOa1S9NO9 TT2T 929 ET9 LP:bt E66t -9t -TT II 1 1 weir section can be spread on top of the corresponding berm which would add free board to the pond for protection against overtopping. I The final parameters for both ponds are as follows: Bast Pond West Pond I Normal Water Level (NWL) 953.9 948.1 High Water Level (HWL) 956,0 950.0 Discharge cfs 52.0 73.0 I Storage Volume AF 1.2 1.1 Outlets: 20' crest weir elevation 955.0 949.0 I 12" Pipe 953.9 --- -- 15" Pipe 948,1 I The proposed storm sewer servicing areas C, D, & E should not discharge directly into the existing culvert under Powers Blvd. We recommend the provision of a sediment trap before discharging into the existing wetland. I A sediment trap with a sedimentation capacity of 3000 cubic feet and a minimum of three feet is recommended. This trap should provide sediment removal without impacting the 1 surroundings significantly. The sediment trap should be located outside the wetland boundary,It is our understanding that a trail will be built between Powers Blvd. and the existing wetland. I The trap will have to be located taking this into consideration. The attached sketch shows a possible location for the trap. This sketch is only for the purpose of illustrating a possible location outside the wetland boundary where it is easy to conform with the natural topography, 1 REC OMMEIV'DATIONS /COM1ViENTS I Runoff resulting from storm events exceeding the 10 year design capacity of the development stormsewers will flow outside the development into important collector streets (Kebler Blvd. and Powers Blvd.). We recommend the modification of the internal drainage to keep runoff within I the proposed development. The wetland shows signs of erosion in the middle of it. Runoff has eroded a small meandering I channel in the middle of the wetland. With this new development the amount of runoff will be increased and with it the amount of erosion. We recommend to define the Normal Water Level NWL for the wetland and provide the proper outlet structure. I The City can consider some cash contribution from the developer to enhance the wetland and other downstream wetlands. This cash contribution can be equal to the cost of the land and the 1 excavation to build proper ponding minus the cost of the actual improvements. If you have any questions or comments, please let me know at ext. 253. I Have a nice day! Y 1 1 vo. •OSSv '8 0021199N08 titi£ti 9£9 ET9 Lt :bti 266S -9Z -tit I 11 -18 -1992 14:49 612 636 1311 BONESTR00 & ASSC. P.C6 .. / I r I : i ,.. ..'` .....„, \‘.. \ '‘.. . ' ... ..s.,.,,, s t / .; ' '.. ; I / ti / ,' ! ( ,. .. / d' N. f fr f • d \ \ i s 7 \ f j 1 t +" y,,, ii , � �` i ? r\ ,.. \ \ N, \ \ f " ( I r � yM1, . , r `` f/ � ` t \ ( ' j . ii # . le' E E !! k 1 a‘ ,,.... ... ,.......... !,, ....icy. z,- -,- &BP. 1 ■ • • ,, , ,, , :, ‘, ., ,, , i. ; i , , .. ( \ _ : t ., ,..... \ \\.1. , . NO : if pi , I : . , ......../.... .4 • .' I : ! ' 1 1 . 414, \ ., ............, ,, \' k � �� , E 1 1 L� • , I It 1 } 1 y` ' • • • t \ \\ ''., t . ., \ ", + i; \, v" "' fit, l \ \\\\\,,, T1.17 \ : ' reVi. 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R; I 1 Section On USGS NWI: Y — N Observer Initials: Er-- Date Visited: 5 /.132_ / 4 2 1 Picture Number(s)/Roll #: 25 / gcl_ Picture Nos.: ) (Sege. S& J - ems ) Classification Wetland Type: Pow F (Cowardin); 5 (Circular 39) Wetland Location: Lakeside Streamside ' Headwaters ✓ Isolated (upland) Edge of Wetland Contour ; varies 1 City Class: (P)ristine ; (N)aturai ; (A)g/Urban ✓ ; (U)tilized 1 Watershed Characteristics 1 Wetland Size: acres Direct drainage area: acres Total drainage area: acres Open water area acres 111 Vegetation 1 Dominant Plant Species: 1 Reed canary grass A Cattail (o -�N•cc Purple Loosestrife: (D)ominant; (A)bundant; (S)ome; (I)ndividua]s; a • ne 1 Plant Diversity: No. Species Dominant 02; 3-5; 7 Percent open water: '5 % 1 1 1 1 Land Use Influences Surrounding Land Use (Percent): 1 ?.a /„ Residentis M, D, Rur. Commercial/Industrial ---- Agricultural - - Open Water 1 20 % Wooded - Institutional - ,7D �, Vacant Field .y. Lip% (describe below) Hydrology 'Water Source: ✓ . Natural; Stormvvater, Unknown I Inflow: Stream; Ditch; 1.-- Stormsewer, Surface Outflow: Natural; Ditch; ✓ Culvert; _. None I Sedimentation/Siltation: Y N Flooded - dead or dying trees: Y ✓ N 1 Drains to 4, -1 z!z N 1,, , , 0-- ,(Direction; Wetland No.) (C)ontinuously; S) nally; (I)ntermittently; (R)arely 1 Soil Classification 1 Soil Type Abby.: Soil Name: 1 Other I r Wildlife Observations: t _.J . General Notes/Comments: u� pA.c -,,� E'. G n. ��• < :Ci 1.y � �G. G, nark f-R i.•- • e-e., h_ tki - _ • I rim •1 fie.pic Y1G: ac,. L; !t ,._d �•-r a E ajL �9 ? • r L 'r ',JP( v�ty„ r �✓� -L I'D 1 Section No. ( t Wetland Sketch; Photo Locations 1 4 1.,,u,r (ct "J'A'-t) 'r 1 s 8 p ,,,,,. 9 12 t7 13 16 J\ 1 Not to Scale 1 Land Use Influences I Surrounding Land Use (Percent): o °i Residen:.DM, D, Rur. -- Commercial/Industrial — Agricultural — Open Water 1 35% Wooded Institutional 15 °i� Vacant Field 4- LI0 (describe below) 1 Hydrology 1 Water Source: Natural; ✓ Stormwater, Unknown Inflow: Stream; Ditch; ✓ Stormsewer, Surface Outflow: Natural; Ditch; ✓ Culvert; __ None Sedimentation/Siltation: Y ✓ N 1 Flooded - dead or dying trees: Y ✓ N Drains to <,� , ‘1 , .,4— . PI —15(1) ; (Direction; Wetland No.) 1 (C)ontinuously (S asonally; (I)ntermittently; (R)arely 1 - Soil Classification Soil Type Abby.: Soil Name: 111 Other 1 Wildlife Observations: -1 r:)' •, General Notes/Comments: �.A(�,,� ',5 S, t..,,�,.....t- ' l Section No. 11 Wetland Sketch; Photo Locations 1 1 4 (" h.k- N 1 5 8 - 7 wsecti 9 12 / /� 1 1 13 16 �' LA L...' 12." PO 1 P e c,/,, 1 4, Not to Scale 1 c v, City of Chanhassen 1 Wetland Observation Records 1 Wetland No.: Z. (Field Review): A I 1 -12 (2) (Official Map) Location 1 Ho T; 23,x;/ R; ►. I Section On USGS NWI: Y L N 1 Observer Initials: Date Visited: / 9_. Picture Number(s)/Roll #:24 AIL z Picture Nos.: 1 CSe.o, k Classification I - Wetland e: ( Cowardin • Circular 39) I Wetland Location: Lakeside Streamside Headwaters ✓ Isolated (upland) 1 Edge of Wetland Contour ; • varies City Class: 1 (P)ristine ; (N)atural ; (A)g/Urban • ; (U)tilized 1 Watershed Characteristics I Wetland Size: acres Direct drainage area: acres Total drainage area: acres Open water area: acres Vegetation 1 Dominant Plant Species: , 1 Reed canary grass 5 Cattail <o a (.o C'r+ e■) I J I: t2 r .}' Li pisti. 1 1 Purple Loosestrife: ( D)ominant; (A)bundant; (S)ome; (I)ndividuals;(•ne Plant Diversity: No. Species Dominant ( 2; 3-5; 7 1 Percent open water: 1;5°49 1 1 . Land Use Influences 1 Surrounding Land Use (Percent): 3p `/o Residen ' D , Rur. Commercial/Industrial I Agricultural Open Water - �,n err, Wooded — Institutional 111 Vacant Field ..,E 40 3/, (describe below) 2 V Hydrology 1 Water Source: Natural; ✓ Stormwater, Unknown ✓ S ormse Inflow. ream; Ditch; re Surface w: , PJC� Outflow: Natural; Ditch; ✓ Culvert; None Sedimentation/Siltation: Y ✓ N 1 Flooded - dead or dying trees: Y ✓ N Drains to ,,, D -'a M 4111 — 12( ►.) ; (Direction; Wetland No.) 1 (C)ontinuously;eS' easonally; (I)ntermittently; (R)arely Soil Classification 1 Soil Type Abby.: Soil Name: 1 • Other 1 Wildlife Observations: rp., p d D . General Notes/Comments: hl a 12,r � ,,.)� .�. 1 G ti f l 1 - ,, -- r), , ACA. (3 � (fi.... y i f>., c-.._,,, y 4 J - -r-. v .4: •-4 . c: t u vro'fl. C4.: ?..�-,lttf n . ra , 1 (Ir! 4- D '' .. r / rL c�k 4. Section No. 11 Wetland Sketch; Photo Locations 1 1 4 Ker,,Ks•.�i -, 04 \: X4 it '�i� (cwt W.i f) . r S 8 � J 1 9 12 _ 41 0 . 13 16 i� ` INAALA- 2 PV C. p' pQ.. Not to Scale 1 1 Qom, • City of Chanhassen Wetland Observation Records Wetland No.: 5 (Field Review): A( 1 - / EC (' (Official Map) Location T; 7 LR; I 1 Section On USGS NWI: ✓ Y N Observer Initials: l Date Visited: 5 //a_ / Q y Picture Number(s)/Roll #:Z? - Z3 /EK2 Picture Nos.: i - ?_ ( c-4 Classification Wetland Type: .11�', (, (Cowardin); _ (Circular 39 7 ) Wetland Location: Lakeside Streamside Headwaters Isolated (upland) r Edge of Wetland Contour q ,0 City Class: (P)ristine ; (N)atural ✓ ; (A)g/Urban ; (U)tilized r Watershed Characteristics Wetland Size: acres Direct drainage area: acres Total drainage area: acres Open water area acres Vegetation Dominant Plant Species: Reed canary grass 5 Cattail • ___ - rr✓ n • r 17urr1: wkt,_c_d_. � ! 14-91 i -! ( 5 { � � A-- i Sri :•� 5 5/4, V` Purple Loosestrife: ( D)ominant; (A)bundant; (S)ome; (I)ndividuals;®one Plant Diversity: No. Species Dominant 1. 2; 3-5; 7 Percent open water: 1 1 1 Land Use Influences Surrounding Land Use (Percent): 10 °i Residen a .0M, D, Rur. -- Commercial/Industrial Agricultural _ Open Water 111 35% Wooded Institutional 5 °r, Vacant Field Wp% (describe below) Hydrology Water Source: Natural; ✓ Stormwater Unknown 1 PJC -F,o Inflow. Stream; Ditch; t/ Stormsewer, Surface Outflow: Natural; Ditch; I/ Culvert; None 1 Sedimentation/Siltation: Y ✓ N Flooded - dead or dying trees: Y L/ N I Drains to f( 0.- 7 , — s (i) ; (Direction; Wetland No.) (C)ontinuously; (S asonally; (I)ntermittently; (R)arely 1 Soil Classification 1 Soil Type Abby.: Sod Name: 1 Other 1 Wildlife Observations: ra,; ',) �( General Notes/Comments: Au,' d,r,,, '15 5,1. �.' el- t,or, 4,4 •.4 l . ,I a..1 1 WbJJ_ c V ie t, i ( ^A4 Section No. 11 Wetland Sketch; Photo Locations 1 4hj- 14 1 5 8 - �e 4e. �� d z Z' 1 9 12 r/ % - 1 13 '16 ' '� Iz PO 1 ty•- Not to Scale :, 1 STATE Of H M M Z ED IM, DEPARTMENT OF NATURAL RESOURCES PHONE NO. METRO WATERS - 1200 WARNER ROAD, ST. PAUL, MN 551RELN0 772 -7910 October 2, 1992 ,z OCT - 1992 Kathryn Aanenson, Senior Planner City of Chanhassen CITY OF 690 Coulter Drive Chanhassen, MN 55317 , RE: OAK PONDS /OAK HILL, CITY 192 -3PUD, CITY OF CHANHASSEN, CARVER COUNTY Dear Ms. Aanenson: We have reviewed the site plans (received July 23, 1992) for above - referenced project (SE 1/4, SE 1/4, S.11, T.116N, R.23W) and have the following comments to offer: 1. The project site does not contain any public waters or public waters wetlands; therefore, no DNR protected waters permit is required. 2. No DNR shoreland or floodplain concerns were noted. 3. It appears that there are wetlands on the site that are not under DNR jurisdiction. The U.S. Army Corps of Engineers should be consulted regarding pertinent federal regulations for activities in wetlands. In addition, impacts to these wetlands should be evaluated by the city in accordance with the Minnesota Wetlands Conservation Act of 1991. 4. There should be some type of dedicated easement, covenant or deed restriction for the properties adjacent to the wetland areas. This would help to ensure that property owners are 11 aware that various agencies (including the city, watershed district and U.S. Army Corps of Engineers) have jurisdiction over the areas and that the wetlands cannot be altered without appropriate permits. 5. Appropriate erosion control measures should be taken during the construction period. The Minnesota Construction Site Erosion and Sediment Control Planning Handbook (Board of Water & Soil Resources and Association of Metropolitan Soil and Water Conservation Districts) guidelines, or their equivalent, should be followed. 6. If construction involves dewatering in excess of 10,000 gallons per day or 1 million gallons per year, a DNR appropriations permit is required. You are advised that it typically takes approximately 60 days to process the permit application. 1 AN EQUAL OPPORTUNITY EMPLOYER 1 1 Ms. Kathryn Aanenson (Oak Ponds /Oak Hill) October 2, 1992 Page 2 Thank you for the opportunity to comment. Please contact me at 772 -7910 should you have any questions regarding these comments. 1 Sincerely, C-cf4 Ceil Strauss Area Hydrologist cc: Lisa Sammon, Glaser Financial Group Gary Elftmann, USCOE Bob Obermeyer, Riley- Purgatory -Bluff Creek WSD Carver SWCD Wayne Barstad, Ecological Services 11 1 1 1 1 1 1 y1i Uf ,���,� off, DEPARTMENT OF THE ARMY ST PAUL DISTRICT, CORPS OF ENGINEERS c;, N 180E KELLOGG BLVD, ROOM 1421 G 111!1 rf ST PAUL. MINNESOTA 55101-1479 � October 30, 1992 REPLY TO ' ATTENTION OF Construction - Operations Regulatory (93- 00103- NP -GAE) 1 Mr. Brad Johnson Lotus Realty P.O. Box 235 Chanhassen, Minnesota 55317 Dear Mr. Johnson: We have reviewed the information provided us about a project proposed by Lotus Realty to grade and landscape an upland area to facilitate residential development (Oak Ponds) at a site located in the SE 1/4 Section 11, T. 116 N., R. 23 W., of Carver County, in Chanhassen, Minnesota. The work proposed at the location stated is not within the regulatory jurisdiction of the Corps of Engineers. No work will be done in a navigable water of the United States, and no dredged or fill material will be placed in any water of the United States, including wetlands. Therefore, a Department of the Army permit is not required to do this work. This letter is valid only for the project referenced above. If any change in design, location, or purpose is contemplated, contact this office to avoid doing work that may be in violation of Federal law. PLEASE NOTE THAT THIS CONFIRMATION LETTER DOES NOT ELIMINATE THE NEED FOR STATE, LOCAL, OR I OTHER AUTHORIZATIONS, SUCH AS THOSE OF THE DEPARTMENT OF NATURAL RESOURCES OR COUNTY. If you have any questions, please call Gary Elftmann of this office at (612) 220 -0355. Sincerel , Ben Wopat Chief, Regulatory Branch Construction - Operations Division Copy furnished: Mr. William Dolan Meadowood Engineering, Inc. Ms. Lisa Sammon Glaser Financial Group Ms. Kathryn Aanenson City of Chanhassen • I/ Planning Commission Meeting December 2, 1992 - Page 1 1 PUBLIC HEARING: WETLAND ALTERATION PERMIT FOR A SEDIMENTATION BASIN ADJACENT TO A CLASS 11 WETLAND AND MODIFICATION OF AN EXISTING SEDIMENTATION POND FOR THE OAK PONDS /OAK HILL PROJECT LOCATED NORTH OF WEST 78TH STREET, BETWEEN KERBER AND POWERS BOULEVARD, LOTUS REALTY. Public Present: Name Address 1 Bob Bohara 7510 Canyon Curve Jack Thien 7570 Canyon Curve Bill Dolan Meadowwood Engineering Kate Aanenson presented the staff report on this item. Batzli: Can you tell us what the status of the overall project is with II City Council? Aanenson: They've submitted everything to date to be on for preliminary approval for the December 14th meeting. Preliminary site plan approval. l Batzli: This is a public hearing. Is there anyone that would like to address the commission? If the applicant is here. 1 Bill Dolan: I'm representing the applicant. Mr. Chairman and members of the Commission. My name is Bill Dolan. I'm a consulting engineer and I'm representing the developer this evening. We have, as Kathy said, II reviewed all the reports and everything and we agree with the reports and the method of handling the storm water. She also eluded to the fact tha they're still working on the costs and of course we want the right to review those costs too. But other than that why we agree with it. Batzli: Okay, thank you. Is there anyone that would like to address this Commission? Jack Thien: Hi. My name is Jack Thien. I live at 7570 Canyon Curve an I'm just curious being that my property is adjacent to that one particular pond on the east end, in what way that might effect my land or my property, if at all. Aanenson: The pond along Kerber? Jack Thien: Yeah. 1 Aanenson: Maybe Dave can specifically. Hempel: The proposed development will not raise the elevation of the pond. The improvements that they're proposing on the pond is to modify the outlet control structure to, as you may be aware of that when we do get a good rainstorm that the water over tops and essentially washes out" the berm from time to time. City crews have gone in and tried to modify that to rectify that problem. In the past there's been cattails and 1 1 Planning Commission Meeting December 2, 1992 - Page 2 debris getting stuck in the pipe itself thus causing the overflow problem. What's being proposed here this evening with the overall development is modifications to those berm areas with what is called a broad crested weir. It's essentially a notch in the berm that provides emergency overflow should 100 year flood take part. That broad crested weir is designed so it will not wash out like it has in the past. That is done with rip rap rock and from an aesthetic standpoint, what is proposed is to backfill over that rip rap material with topsoil and re- establish the vegetation so you will have, similar to what is out there today with the exception of the elevations. There will be a, I believe it's a 20 foot wide gradual slope with a V notch so at the low point of the overflow, be approximately 18 inches lower than the rest of the berm. Bob Bohara: Bob Bohara, 7510 Canyon Curve. Where is this sedimentation, new sedimentation pond going to actually go? Aanenson: This is Powers Blvd. The edge, would be the southerly edge. Bob Bohara: Right at the edge of the road there? My only concern was, as on the road side, that's very steep there and going up the other way it's also, it's not as steep but it's still fairly steep there and I don't know where you're going to get any significant volume of water in that area without significant cuts and they're already cutting from the top to add that road on there so I don't see how it all goes together. 1 Hempel: Mr. Chairman, I can address that. Essentially what they're providing here is a sediment trap or sediment basin. It is not designed to handle the 100 year storm event. It is designed to handle the 5 to 10 ' year type storms which our storm sewers are designed for. It's strictly for a sediment removal prior to discharging into the wetlands and further on down the stream. Bob Bohara: Is there going to be erosion problems from the road side? Or you don't know yet? Hempel: Well we. don't believe so. Not with the measures, the slopes I believe will be a 3:1 slope and will be re- vegetated with native grasses and so forth. Bob Bohara: How close to the actual roadway... Hempel: It is outside the road right -of -way. Aanenson: And the bike trail. Hempel: And the bike trail, that's correct. Bob Bohara: That was the next question. How does that, and were you 1 going to have to build up for the bike trail too or something? Hempel: I believe the bike trail will be basically notched into the side of the hill and a retaining wall possibly on the inside slope to retain that. 1 1 Planning Commission Meeting December 2, 1992 - Page 3 1 Batzli: As you have it illustrated Kate though, the dark line is the II right -of -way line. That's not the edge of the tar, is that correct? Aanenson: Correct. Bob Bohara: Okay. Batzli: Thank you. Is there anyone else that would like to address the Commission? Is there a motion to close the public hearing? Conrad moved, Erhart seconded to close the public hearing. All voted in favor and the motion carried. The public hearing was closed. Batzli: Joan, do you have any comments? Ahrens: No. Except for on condition number 4. I think it should read cash contribution in an amount determined by the City. Batzli: Anything else Joan? Jeff. 1 Farmakes: No comments. Batzli: Steve. Emmings: No. Ledvina: I did have a few questions and number one, a general comment that I have and it relates to the report itself. I know that there mighll be some concern to work this through to City Council and I don't know maybe catch it up with the other things that are going on with the site but we talk about the drainage plan for this project and throughout the staff report we've cited areas C, D, E and G, etc. And from the information that's given to us we really can't evaluate what those drainage areas are. Aanenson: You should have been given a drainage plan with this. Ledvina: We do have a water plan with this but it doesn't, to my, maybe" I didn't catch it but I don't believe that there's a delineation of how the different drainage areas, from what I saw. So I think that would have been helpful. Aanenson: That was a mistake. You obviously got the wrong set of plans. You should have gotten a copy of them. Ledvina: There's a different set of plans that goes with this proposal?" Aanenson: Yeah. There's one that shows the A, 8, C, yes. Ledvina: Okay. So that was a concern that I have. I think that from m evaluation of what's provided here, it all seems to fit together but I don't have a real solid way of making my evaluation. So just in the" future if we can make those changes. Or I'm sure that's, we have the information that should be provided that's discussed in the staff report. 1 1 Planning Commission Meeting December 2, 1992 - Page 4 One of the comments from the engineer's report relates to the erosion of the wetland. Currently there's a meandering channel in the middle of the wetland, as I understand. The engineer's indicated that the flow rate from or the flow to the wetland as a result of this development will increase. I guess I don't understand what the provisions are going to be to mitigate this situation. It seems to indicate some work, some additional work that would have to be done downstream and if that's not part of this project, how do we insure that that happens without further damage to the wetland? ' Hempel: One of the improvements proposed at these berms is what we call a surge basin at the bottom of the outlet to dissipate the energy of the runoff through the storm pond. The water quality issue is being dealt further downstream with the Eckankar pond. That pond has been designed to take in the consideration the additional runoff generated from this site. We're controlling the runoff underneath Powers Blvd with a control rate structure so that we maintain the pre - developed runoff rate on this 1 site and underneath the culvert to the west of the Eckankar property. Ledvina: Okay, so you mentioned a surge basin at the outlet of the 1 wetland, is that correct? Hempel: At the berm, yes. The downstream side of the berm at the outlet. The end of the outlet pipe, that's correct. Ledvina: Okay, is that part of this proposal? ' Aanenson: The second retention pond you're saying? Hempel: The second retention pond. 1 Ledvina: Oh, the second retention pond. Aanenson: Not the wetland. Ledvina: How does that deal with the issue as it relates to the erosion 'and the wetland which is downstream from the second retention? 1 Hempel: That erosion we believe has transpired over the last few years with the overtopping of these two storm retention ponds. By correcting the outlet of these two retention ponds and providing surge basins, we 1 hope to mitigate the erosion downstream. Ledvina: So by equalizing the flow, we won't have a situation where 1 there will be a concentrated large volume of flow? Hempel: That's correct. We're hoping to regulate it and keep the velocities down. Ledvina: And you believe that will be the case even though the volume, the runoff volumes are? Hempel: Based on the hydraulic models our storm water consultant has provided, he's comfortable with the proposal. 1 1 Planning Commission Meeting December 2, 1992 - Page 5 Batzli: Ladd? 1 Conrad: Nothing. Batzli: Tim? 1 Erhart: I don't have anything. Batzli: My only comment is somewhat technical and that is, the motion that we adopt, we should probably recommend approval of the wetland alteration permit rather than approve it and we should probably do it in 1 accordance with the plans stamped October 22nd? Or is there a different set? Or should we do it in accordance with the staff report? Aanenson: I'd do it with the staff report because it's, his map's in 1 here and that's really what it, yeah. Batzli: Okay. Is there a motion? 1 Erhart: I move that the Planning Commission recommends approval of Wetland Alteration Permit #92 -11 with the conditions listed in the staff l report and as described in the staff report. Emmings: Second. Batzli: I'll call for discussion and then I'll ask if you would be willing to modify condition 4 in accordance with Joan's request to read a cash contribution as determined by the City to the Surface Water Management Program Fund. Erhart: Sure. Batzli: Second, do you accept that? Emmings: Yeah. 1 Batzli: Is there any other discussion? Erhart moved, Emmings seconded that the Planning Commission recommend 1 approval of Wetland Alteration Permit #92 -11 with the following conditions: 1. The limits of the sedimentation trap shall be limited to the 944.0 1 contour adjacent to the Class ss B wetland. 2. The existing two storm water ponds shall be limited to modification proposed including the weir and outlet structures. 3. Type III erosion control be in place around the construction boundar .s of the wetland. 4. A cash contribution in an amount determined by the City to the Surface Water Management Program Fund. All voted in favor and the motion carried. 1