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HomeMy WebLinkAboutDrainage Reports - 06/23/1993 (2)i New Final Approved Repoli -' Date 6' 3 X3 THIS Y AND FINAL DRAINAGE STUDY AND REPORT FOR SUNSTONE AG 7T UBDIVISION (FILING 7) WAS PREPARED BY LAND SERVICES USING THE CITY OF FORT COLLINS STORM DRAINAGE DESIGN CRITERIA, dated May, 1984. The results of this drainage study are reported in the enclosed text and supporting documents, and are shown in further detail on the Utility Plans submitted concurrently with this report. This report is a revised version of the original report dated May 30, 1992, a second report dated June 30, 1992, a third report dated September 10, 1992 and.a fourth report dated April 28, 1993.. Signed this ftL-day_aE-May, 1993. Dennis L. Donovan, P.E. Land Development Services 309 W. Harmony Road - Unit A Fort Collins, Colorado 80526 Phone (303) 225-9244 SUNSTONE VILLAGE 7TH SUBDIVISION P.U.D. 01 PRELIMINARY AND FINAL STORM DRAINAGE REPORT I. GENERAL INFORMATION Sunstone Village 7th Subdivision P.U.D. (i.e. Sunstone 7th filing) is a proposed single family subdivision in the City of Fort Collins, Colorado. The site is generally located east of Timberline Road and north of Harmony Road in southeast Fort Collins. A general Vicinity Map is provided at the end of this report. The Sunstone Village 7th filing is a part of the Timberline Farm P.U.D., which consists of the West 1/2 of the Southwest 1/4 of Section 32, T7N, R68W, Sixth Principal Meridian, Larimer County, Colorado. The proposed 7th filing development consists of 28 lots on 7.62 acres, which is consistent with the approved Master Plan. The 7th filing is bounded on the north by Sunstone Village 6th Subdivision P.U.D. (6th filing), on the east by Harmony Village Mobile -Home Court, and on the south and west by undeveloped land that is also apart of Timberline Farm P.U.D. The 7th filing of Sunstone Village is a part of the property identified in the "Master Drainage Report for Timberline Farm P.U.D." (i.e. Master Drainage Report) prepared for the City on behalf of G T Land., Inc. by Engineering Professionals, Inc. (EPI) of Fort Collins. As identified i is located partially in Drainage Tract 2. shown on an Exhibit Drainage And Utility drainage and utility C. n the Master Drainage in Drainage Tract 1, The location of the to the Master Drainage Plan". That drawing plan) is included in Report. the 7th filing Phase `B' and partially drainage Tracts are Report titled "Master (i.e. the referenced this report as Exhibit The Master Drainage Report referenced in this report is EPI Project No. 248.8 dated September, 1989, Revised November, 1989. The report--i.tself is quite lengthy and, other than the inclusion at Exhibit-G, is not attached as a part of this report. The report is available at the Stormwater Utility Department of the City of Fort Collins. The Sunstone Village Subdivision consists of four (4) filings of single-family residential lots that were developed ° prior to inclusion of the Timberline Farm P.U.D. Portion.of the Sunstone Village development. The 5th filing was the first Sunstone Village phase of development located within the Timberline Farm P.U.D. boundary. In conjunction with the Master Drainage Report for Timberline Farm P.U.D,. EPI prepared both the Preliminary and Final Drainage Reports for Sunstone Village 5th Subdivision P.U.D. This office prepared the Sunstone Village Subdivision P.U.D. 6th filing "Preliminary and Final Storm Drainage Report". Fl SUNSTONE VILLAGE 7TH SUBDIVISION P.U.D.- PRELIMINARY AND FINAL STORM DRAINAGE REPORT All of the Sun'stone Village Subdivision (including the Timberline Farm property) is located within Reach 2 of the City designated Fox Meadows Drainage Basin. The Master Drainage Report for Timberline Farm P.U.D. by EPI not only reported the storm drainage considerations for Sunstone Village P.U.D., but also updated/modified the Fox Meadows Master Plan. Basin wide improvements are required for all of the City Designated Storm Drainage Basins. Certain basin storm drainage improvements are identified in each of the Drainage Basin Utility Construction Plans. Drainage Basin Fees are collected in each City designated basin to offset the anticipated cost of basin wide improvements. Information regarding the City designated Fox Meadows Basin can also be obtained in current form at the City Stormwater Utility Department. The land contained within the 7th filing has historically been used for agricultural purposes. The site is at a ridge between previously irrigated farming plots, however, there are no active irrigation ditches within the site. No stormwater runoff will discharge onto the 7th filing from off —site. The historic irrigation water flowed to -the north and south from the ditch along the ridge line in the 7th filing. The northern portion of the 7th filing is a part of Drainage Tract 1, Phase 'B' that drains northeasterly from the site. The southern portion of the 7th filing is a part of (Master) Drainage Tract 2 that flows southeasterly into drainage and detention facilities to be completed with the 7th filing improvements. Storm runoff from the northern portion of the 7th filing will drain directly into an existing storm drainage system in the 6th and 5th filings. The existing drainage system downstream includes streets, inlets, culverts, swales and detention Pond/basins. Storm --runoff from the north side -of the 7th filing — along with the entire 6th filing - will flow directly (undetained) through the` drainage system into the existing detention pond in the northeast corner of the 5th filing. The detention system downstream in the 5th filing was designed to accommodate direct (undetained) storm runoff from the .6th, and northerly portion of the 7th, filing. Accordingly, no detention .facilities for Timberline Farm nor basin —wide improvements for the Fox Meadows Drainage Basin were required for the 6th filing nor the northerly Portion of the 7th filing. Storm runoff that flows southerly through 'the 7th filing drainage system to the new detention pond on the south side of the 7th filing (i.e. Detention Pond No. 1) will flow easterly through the detention pond to an 18 inch culvert at the 2 SUNSTONE VILLAGE 7TH SUBDIVISION P:U.D. PRELIMINARY AND FINAL STORM DRAINAGE REPORT downstream end of the pond. A two foot wide concrete trickle channel at a minimum 0.2 percent slope to the -east will allow for low, nuisance type, runoff to pass through the pond. The detention pond is located within Tract A of the 7th filing (see the final plat) and within additional property south of the 7th filing which was included as a part of Detention Pond No. 1 by agreement with the adjacent property owners to the south. The release structure from Detention Pond No. 1 is an 18 inch pipe culvert daylighting into a drainage swale approximately 200 feet south of the northeast corner of the 7th filing. The Previous plans for this project reflected an additional 60 foot long culvert just upstream from the release point into the 6th filing. The 60 foot long culvert has been eliminated in the final drainage plan and replaced with a 2 foot wide trickle pan in the drainage Swale. The small ponding area that was shown upstream of the 60 foot of culvert does not provide enough effective detention to be included in the plan, as the only area draining directly into the small pond was from the back yards of Lots 14 thru 18. That portion of D.A. #7-2 contains only 0.42 acres. The peak discharge from the back yard areas into the Pond/swale area is about 1.5 cfs. The stormwater runoff volume from such a small area is less than 0.03 acre feet. Five (5.0) acre feet of detention volume are provided in the downstream Detention Pond #2, so the impact of deleting the 60 foot of culvert is minimal. In fact, the additional depth required to store the 0.03 ac—ft across the surface of the 2.5, or so, acre surface of Pond #2 is about 0.01.feet. The result of removing the unnecessary 60 foot of culvert is insignificant to the overall drainage plan. From the drainage swale at the outlet to the 18 inch culvert, st-9rmwater discharge will flow northerly through the drainage swale to be constructed in the northeast corner of the 7th filing`;= through an existing drainage Swale on the east side of the 6th (and a portion of the 5th) filing, and into the existing detention facility at the northeast corner of the 5th filing (Detention Pond No. 2 on the Master Drainage Plan). The southerly portion of Sunstone 7th filing, as well as the future Retail/Business Park south of Sunstone 7th filing (which extends to Harmony Road), will contribute storm water runoff to Detention Pond No. 1 (as designated on the Master Drainage Plan). Construction of the majority of the detention pond facilities will occur with the 7th filing development. 3 SUNSTONE VILLAGE 7TH SUBDIVISION P.U.D. PRELIMINARY AND FINAL STORM DRAINAGE REPORT At such time as the commercial area to the south develops, it is a requirement that the additional detention facilities and other overall drainage improvements relative to Detention Pond No. 1 will be designed and completed. II. Proposed Storm DrIainage Plan The proposed drainage plan for the 7th filing is in compliance with the Master Drainage Report. The site has been divided into eleven (11) sub basins for design purposes. Nine sub basins (i.e. D.A. 7-1 through D.A. 7-9) will contribute storm runoff from the 7th filing into existing or proposed downstream drainage and detention facilities. For design purposes, Tract A of Sunstone 7th filing is considered a sub basin within Detention Pond No. 1. The offsite sub basin to the south of Tract A is also a portion of Detention Pond No. 1. The two sub basins (i.e. D.A. TA-1 and D.A. 0-1) constitute the entire detention pond limits required for the 7th filing. The two sub basins comprising Detention Pond No. 1 have been identified because they also contribute to the storm runoff design considerations for the 7th filing. The 9 sub basins within the 7th filing, and the 2 sub basins that contain Detention Pond No. 1 are identified at Exhibit A, which is the Grading and Drainage Plan (Sheet 6 of 7) of the Utility Plans for the 7th filing. Exhibit B (identified as the Overall Drainage Map for the 6th filing) is also included at the end of this report to identify drainage basins expected for the 7th filing during design of the 6th filing. The nine sub basins resulting from the 7th filing design do not vary significantly from the patterns shown on Exhibit B. The storm drainage basins (i.e. Sub basins 0-1 and 6-4) identified during the 6th filing storm drainage report were estimated .fo-contain 2.77 acres and have 2 and 100 year peak discharges;�of 3.7 and 13.9 cfs. The same sub basins identified during the 7th filing evaluation and report contain 2.95 acres, and 2 and 100 year peak discharges of 3.9 and 14.1 cfs. These differences are insignificant. In the 7th filing, Sub basin #7-1 will flow in the easterly curb and gutter of Stoney Creek Drive into the 6th filing (shown as Design Point #1 at Exhibit A). Storm runoff from sub basins 7-3 and 7-4, as well as sub basin 4 from the 6th filing, will flow in the westerly curb and gutter of Stoney Creek Drive into the 6th filing (shown as Design Point #2 on Exhibit A). At the intersection of Creststone Court and Stoney Creek Drive, the storm runoff from the above identified sub basins will be joined by runoff from sub basins within the 6th filing. The SUNSTONE VILLAGE 7TH SUBDIVISION P.U.D. PRELIMINARY AND FINAL STORM DRAINAGE REPORT flows from the contributory sub basins in.the 7th and 6th filings from Stoney Creek Drive at Crestone Court to the east to the drainage Swale between Lots 31 and 32 (6th filing) will not vary significantly from the amounts estimated in the 6th filing report. According to the Master Drainage Report, the Timberline Farm P.U.D. area south and.west of the 6th filing will drain to and along the Drainage Tract on the east side of the 6th filing. However, the storm water detention facility to be constructed at the south end of the 7th filing, as well as on the northeasterly most portion of the off —site commercial area to the south, will limit the discharge during a 100 year design storm to 12 cubic feet per second (cfs). As a result of the uncertainty of the ultimate drainage sub —basin stormwater runoff patterns and other storm drainage characteristics for .the currently undeveloped off —site commercial area to the south and the multi —family property to the west of the 6th and7th filings, final design of the storm water detention on the south and east side of the 7th filing can not be finally determined at this time. At the time of development thereof) the storm drainage and required by the City to meet or and earlier studies and reports of those properties (or portions erosion control design will be exceed criteria intended by this for this area. The Master Drainage Report identifies a pipe culvert and overflow swale to carry storm runoff in the Tract on the east side of the 7th and 6th filings between the proposed detention facility to the south and the existing detention facility in the 5th filing. For whatever reason, the culvert was ommitted in the fifth filing design — leaving the drainage Swale as the only runoff carrying facility between the two detention ponds. The swale connecting the existing and proposed detention facilities in the 7th filing .(as identified on Exhibit A of the 7th filing report) needs to be lowered by one (1) foot from the design grades identified on the original 6th filing design and report. This modification'is warranted to lower the minimum invert elevation of Detention Pond No. 1 to 4954.62, which is just slightly higher than anticipated by the Master Drainage Plan. The Swale and detention facility grading plan for the easterly and southerly portion of the 7th filing is shown on Exhibit A. The detention pond (No. 1) requires a detention volume of 3.8 acre feet, according to the Master Drainage Plan. As designed (see the grading on Exhibit A), the.detention pond has a volume of about-3.1 acre feet as designed. 5 SUNSTONE VILLAGE 7TH SUBDIVISION P.U.D. PRELIMINARY AND FINAL STORM DRAINAGE REPORT and 7-9 will also contribute storm runoff to the detention pond. The location where the concentrated flows enter the detention Pond is identified as Design Point #4 at Exhibit A. A temporary swale, riprap and the 15 inch storm sewer system carrying storm runoff from Design Point #3 will be provided to drain the reach of Milestone Drive to be constructed for Sunstone Village 7th filing. When Milestone Drive is extended to Timberline with the development of the commercial land to the south of Sunstone, inlets will be constructed just south of the 7th filing to replace the temporary swale and discharge storm runoff into Tract A. Storm runoff from sub basin 7-5 will sheet flow into 'drainage swales (for which easements were provided in the 6th filing) on lots to the east of the 7th filing. Storm runoff from sub basin 7-6 will flow northerly into the 6th filing along Winterstone Court. The sub basin flow is relatively minor and does not adversely impact the downstream system in the 6th and 5th filings. The Hydrologic Characteristics for the sub -basins in the 7th filing, for the small off site sub basin in the 6th filing (i.e. 6-4) that contributes storm runoff to the 7th filing at Design Point #2, as well as for the combined sub basins at Design Point #'s 3 and 4 are included on the following page as Table 1. 'No TABLE 1 HYDROLOGIC CHARACTERISTICS SUNSTONE VILLAGE 7TH FILING 2 YEAR 100 YEAR BASIN AREA C VALUE TIME OF TIME OF i 2-YR i 100-Y Q 2-YR Q 100-YR DESIGN DESIGNATION CONCEN- CONCEN- POINT TRATION TRATION (ACRES) (MIN) -(MIN) (in/hr) (in/hr (CFS) (CFS) 7-1 1.50 0.6 13.3 12.3 2.2 6.5 2.0 7.3 1 7-2 1.45 0.3 10.0 10.0 2.5 7.2 1.1 3.9 7-3 0.65 0.6 10.0 10.0 2.5 7..2 1.0 3.5 7-4 0.65 0.3 13.3 12.3 2.2 6.5 0.4 1.6 7-5 0.30 0.3 10.0 10.0 2.5 7.2 0.2 0.8 7-6 0.50 0.6 10.0 10.0 2.5 7.2 0.8 2.8 7-7 0.71 0.6 12.3 10.3 2.3 7.0 1.0 3.7 3 7-8 0.38 0.7 10.0 10.0 2.5 7.2 0.7 2.4 7-9 0.20 0.9 10.0 10.0 2.5 7.2 0.5 1.6 6-4 0.15 0.3 10.0 10.0 2.5 7.2 0.1 0.3 A-1 8 0-1 1.91 0.3 16.2 11.1 2.0 6.9 1.1 4.9 COMBINED FLOWS 7-3,7-486-4 1.45 0.45 13.3 12.3 2.2 6.5 1.4 5.3 2 7-7,7-887-9 1.29 0.68 14.3 11.3 2.1 6.8 1.8 7.5 4 7-7,7-897-9 3.20 0.45 23.9 16.1 1.7 5.8 2.5 10.4 5 +TA-1 8 0-1 NOTE: "C" VALUES ARE BASED ON 0.3 FOR LOT REAR YARD AREAS, 0.6 OR 0.7 FOR FRONT YARD AND STREET AREAS, AND 0.9 FOR STREET RIGHT OF WAY AREAS e FA SUNSTONE VILLAGE 7TH SUBDIVISION P.U.D. PRELIMINARY AND FINAL STORM DRAINAGE REPORT The Time of Concentrations were determined using the equation for overland flow in the design manual, and then by adding the time of gutter flow - which was estimated to be at a velocity of 1.5 feet per second for the 2 year storm and 3 feet Per second for the 100 year storm - to the point of discharge from the particular sub basin. The formula for overland flow Time of Concentration is: Tc = C1.87 (1.1 - CCf) D1/21 / S1/3 The sub basins in the 7th filing are relatively small. The maximum time of concentration for any of the sub basins .in this filing is just over 13 minutes for sub basin 7-1. A 10 minute minimum time of concentration was used for sub basins 7-2, 7-3, 7-5, 7-6, 7-8 and 7-9. The Time of Concentration for combined sub basins at the Design Points is determined using the longest time of concentration for any of the sub basins contributing at that point. The longest time of concentration was 23.9 minutes during a two year storm and 16.1 minutes during a 100 year storm at Design Point 5, which is the downstream end of Detention Pond #1. III. DESCRIPTION OF STREET FLOWS AND DRAINAGE IMPROVEMENTS Due to the relatively small areas of the sub basins that will contribute storm runoff from the 7th filing, the concentration of discharges in the street gutters will be somewhat minor. The largest flow in a gutter will be from sub basin 7-1. There a 2 year "minor" design discharge of 2.3 cfs is estimated, and a 100 year "major" design discharge of 8.1 cfs is estimated. The slope of the street at that location is 1.6 percent. According to Figure 4-1 of the design manual and using the following criteria: Cross Slope of 2 %, so a Reciprocal (Z) of 50; a RougMhess Coefficient (n) of 0.016 from Table 4-3; an allowable depth of flow in the gutter of 6 inches during a two year storm: and an eighty percent reduction factor, the gutter will carry about 25 c.fs before exceeding City criteria for the two year, or Minor, storm. .That capacity is about three times the 100 year storm discharge at Design Point 1. Obviously, street gutter flows in the 6th filing are well within City of Fort Collins criteria. Storm drainage facilities, or improvements, for the 7th filing include cross pans at the intersection of, Stoney Creek Drive and Touchstone Court, a 2 foot sidewalk culvert into Stoney Creek Drive from the drainage swale on the north side of Lots 13, swale and detention improvements in the drainage tracts, and CJ r SUNSTONE VILLAGE 7TH SUBDIVISION P.U.D. PRELIMINARY AND FINAL STORM DRAINAGE REPORT an inlet and storm sewer from the north side of Stoney Creek Drive at Milestone southerly under the easterly curb and gutter of Milestone to the west end of Detention Pond #1. Also, a drainage Swale with concrete pan is required on the rear of 7th filing Lots 6 thru 13 to intercept flows and pass the runoff to the sidewalk culvert near the northeast corner of Lot 13 and into Stoney Creek Drive. Cross Section D—D is provided at Exhibit A that provides hydraulic characteristices of the swale along the rear lot lines. the sidewalk culvert will pass most of the 100 year storm under the 2 foot wide steel grate. City Practice indicates 1 or 2 percent of the 100 year flow should pass under the sidewalk culvert, so the 2 foot sidewalk culvert is more than adequate in this location. During the interim time prior to development of the commercial ground to the south and southwest of the 7th filing, the proposed detention pond in the southeast corner of Sunstone Village will be oversized beyond that required for storm runoff from the 7th filing. The runoff from sub basins 7-7 thru 7-9 will be temporarily carried into the detention pond with a temporary drainage berm/swale at the south end of Milestone Drive to be constructed in this phase. When completed, landscaped, and subject to a warranty period for the improvements, the City of Fort Collins has agreed to accept ownership of the drainage tract for future maintenance of the integrity of the drainage capacity. As shown on Exhibit A as Design Point 3, the inlet on the north side of Stoney Creek Drive will only receive about 1.0 cfs during a 2 year storm, and 3.7 cfs during a 100 year storm. Figure 5-2 of the City Drainage Criteria manual shows a theoretical capacity of 1.2 cfs per foot of length within the allowable 6 inch depth and 8 inch heigth of opening for the 2 Year storm. A Reduction Factor of 80 percent shows 0.96 cfs per foot actual capacity. The four (4) foot inlet will accomodate 4 times 0.96j;--9r 3.84 cfs. .This is more than the 100 year storm discharge,_�so a four foot inlet is more than adequate to accomodate"'those flows within City Criteria. A 15 inch storm sewer (City of Fort Collins minimum size) will easily pass these flows to the detention pond with insignificant depth of flow in the culvert. Hydraulic calculations are provided immediately after this sheet to show the performance of the 15 inch culvert under Milestone, as well as the 18 inch culvert releasing stormwater from Detention Pond #1. In summary, the proposed storm drainage for the Sunstone Village 7th filing is -rather minor in scope, and the resulting storm drainage system should adequately protect life and property on the site. 11 owl Ig Xp RP T! 7 7.; w..s % % IG*' % OUTu"K % % 19 10 KWP IP rp bP I p'! I ;7RE7... 4 . I . 0 jLbL 5 .:f. e oc 0 RL'P HLP LLI ca IP p ....... ... 00 v z me IL 'HARMONY ROA bp/-, IP w bp 1p T IP rp rp U� I T 4. ;!A 1: vi @MAP bp TttFiLtAjG E7 dp JOB l�J STQ ISI E TH �/ L Af G INTERMILL LAND SURVEYING INC. $MEET NO. OF 1301 North Cleveland Avenue LOVELAND, COLORADO 80537 CALCULATED BY // DATE /1na\ "a -Az l a Ui W 0 o� IMan F -Ic M � fl U —!- W I I A113013A (�(� 1 1311fl0 W _ r n C) O ~ ~ rN Z U' ltl W Q p p N1110111NO3 �l 1' 39 x W Q �Q�.,� U) N "I > W > n n Q cc w J W W x U O Z I � Z H N N = V 2 Z . Q X s W Ltd I i J N t\1 W x w O � J o yl F G H x t O It. 2 u 3c x IN U O O '� ...� cr W ►- Z Q 11 I1 ct F Z p �I O W 2 MOC 4' 00 �1 ; O 5 M H J a 1.- e ' x zi-- J J a a O --� _ 0 W W l J _j n o O tu Via! w J ; x 4i LO W p W W N< CO8 Z O Z Q Q W Q� d 3 3� O o u W! Z Z %J 'T' 4 . O H ` \� Q 3h ?a Z Y .: •k f y v t. O U O a v F- C9 ��1S J j� W 3; O do U W W 0 O Q O 11 11 r �N d' q N 0 0 C s J O m -QO��� F_ N a K 0.Q = jL I W A` W U W WWI U O - A a t V) "W" M-M Figure 6-1 DESIGN CbMPUTATION FORM FOR CULVERTS MAY 1984 6-2 DESIGN CRITERIA W 1 � F 1 IMallN tl O U [\ �V a + o J W I I A110013A A31Afl0 Cn N z f- `�y� V v w O N1110Y1N00 F 3 H W Q Y F 7� U q W W O O n n>> I x w J Q z S O W W U z I 0: C F � N N JQ z Q x S W W Q J Ln w J = J W 0 x r > a n ; 0 x x 2 I J 0 0-I W w H t1N J z I I 11 f 2 e - O �� Z z z 3 U 0 0 0 0 ,. e o a s ° _ C < >> a W W 0: 0 _ O U. OC O J J of O w N Z w W W Ccc Z N w z �� c� 1 Q Q W 3 3 .4all $ S z z o In x � _�� X C Z O O UI LU Nl W S Q H U O J w o U „ ,. y W 3 O 3 11 1/ N z0 a �- a =�� T �w uo : a >c ,o° 2j H 1 X1. I I Flinn Orm Figure 6-1 DESIGN COMPUTATION FORM FOR CULVERTS MAY 1984 6-2 DESIGN CRITERIA INTERMILL LAND SURVEYING, INC. 1301 North Cleveland Avenue LOVELAND, COLORADO 80537 (303) 669-0516 MO VZ6-14EMk One. MW M To OaMdE TOLLM@M*Mm Joe $MEET NO. OF CALCULATED BY DATE ` _IZ— 13 CHECKED BY DATE MOPJVM /A�lft Gi .11 Ml TGO�M l70LL!�QY07mm NgpJC}WIA�RGl MWOuts T4" POO TOU-U'ilAm THIS PRELIMINARY AND FINAL EROSION CONTROL PLAN REPORT FOR SUNSTONE VILLAGE 7TH SUBDIVISION (FILING 7) WAS PREPARED BY LAND DEVELOPMENT SERVICES USING THE CITY OF FORT COLLINS EROSION CONTROL REFERENCE MANUAL for Construction Sites, dated January, 1991. The results of this erosion control study are reported in the enclosed text and supporting documents, and are shown in further detail on the Utility Plans submitted concurr.ently with this report. This report is a revised version of the original report dated the 30th day of May, 1992 and a second report dated June 30th, 1992. Signed this loth day of September, 1992. Dennis L. Donovan, P.E. Land Development Services 309 W. Harmony Road - Unit B Fort Collins, Colorado 80526 Phone (303) 225-9244 r 0 SUNSTONE VILLAGE 7TH SUBDIVISION P.U.D. PRELIMINARY AND FINAL EROSION.CONTROL PLAN REPORT The erosion control concepts and general design considerations for the Sunstone Village 7th Subdivision P.U.D. (7th filing) are outlined in the following paragraphs and shown in further detail on Exhibit A. The exhibit is the same as for the storm drainage report, and is Sheet 6 of 7 of the Construction Drawings titled OVERALL GRADING; DRAINAGE 8 EROSION CONTROL PLAN. It was determined from the reference manual and a Wind Erodibility Zone Map that the Erodibility Zone for both Rainfall Erosion and Wind Erosion is moderate for the site. Standard Form A "RAINFALL PERFORMANCE STANDARD EVALUATION" follows this text. It identifies the two areas of concern for an erosion control Plan and identifies their pertinent basin characteristics. Sub basins 7-1, 7-3 and 7-4 will drain to the northeast corner of the site, thru the 6th filing and finally exit into the existing swale and detention facility in the 6th and 5th filings. That area requires a Performance Standard of 79.9 Percent from Table 5-1 of the manual. Sub basins 7-2, 7-7, 7-8 and 7-9 will flow into the detention pond on the south and east side of the 7th filing. Table 5-1 indicates a required Performance Standard of 77.6 Percent for this area. Sub basins 7-5 and 7-6 will flow into the 6th filing at the northwest corner of the 7th filing. Standard Form.B "EFFECTIVENESS CALCULATIONS" follows Form A and identifies the recommended erosion control measures and their effect on the site. Sub basins 7-1, 7-3 and 7-4 contain 2.8 acres, of which 0.42 acres will be concrete and pavement. About one-third of the remainder will not have to be disturbed during the overlot grading activities. Rainfall erodibility deterents include a filter over. ---the sidewalk culvert at Stoney Creek Drive, and an existing sediment basin with trap in the drainage tract.at the northeast corner of the 6th filing. The sediment basin in the sixth filing was sized to accommodate sediment from these sub basins. The combination of the improvements for sub basins 7-1, 7-3 anf 7-4 yields an Effectiveness of 89.4 %, which is more than the 79.9 percent Performance Standard required. In sub basins 7-2, and 7-7 thru 7-9, the area is 2.74 acres. Of that, a relatively large area of 1.45 acres will be almost entirely left in its natural undisturbed state. Sidewalk and paving will cover=another 0.25 acres of the area). By planting the disturbed area in -temporary crop cover after grading, an effectiveness of 88.6 % is achieved. This is in SUNSTONE VILLAGE 7TH SUBDIVISION P.U.D. PRELIMINARY AND FINAL EROSION CONTROL PLAN REPORT excess of the Performance Standard required. The detention pond, or area, will also function as a :settling basin for these sub basins. Sub basins 7-5 and 7-6 are only 0.E2 acres in size. The areas in these sub basins should be reseeded after utility installation to minimize erosion impacts on the downstream property. Additionally, the downstream properties have erosion control improvements so that there will be no significant impact from erosion in this area. To minimize wind erosion from the site it is recommended that the northwest perimeter of the site be provided barriers of some type. Snow fence, hay bales, windrows perpendicular to the northwesterly winds would each be a helpful improvement. The construction schedule for the project is to begin grading in early September, 1992. It is a relatively small phase of development, so it is anticipated that grading should only take 2 or 3 weeks. After the grading is completed in early October, utility installation will continue into mid -October. The reseeding activities required should occur when the utilities are completed in late October. During construction, adequate watering of haul roads and areas being graded during construction should also be provided. Standard Form C Follows Form B to identify the Construction Schedule and timing for installation of erosion control measures. The erosion control measures should be maintained by the developer until the majority of homes and landscaped lawns have been completed and the developer is allowed by the City Engineering Inspector to remove the sidewalk culvert filter and the hay bales, and to fill in and landscape the sediment basin. RAINFALL PERFORMANCE STANDARD EVALUATION ------------------------------- PROJECT: 5UN15TO9F -- ------------------ VILL,4Ge 75LQ?o Po STANDARD FORM A COMPLETED --------------------------------------------------------------------- BY: _ Paoi n i s L . Donn✓AN )�sV DATE: � —10-cf - DEVELOPED{ERODIBILITY1 Asb I Lsb Ssb Lb Sb PS SUBBASIN ---- ---- ZONE ------- (ac) ------- (ft){ - I -- (%) .{(feet) -------II { W I W 7-I,-7-3 Moa. 2,8 { 5Z0{ ).Z5 ------ 1 5& --- ----I------- ! 1.25 79,9 7-4 7-7 MoJ , {� 2,7 �- { 56 � C .� i �-f 50 { 1.6 i -77• a B�q � r 1 I ! I I -7-,6 1 14v4, 1 0.5Z12501 1.Z512501 I,Z51 7%, -7- 5 med. f 6,30 00 l,o )0 0 r 1.0 I-71-.� n I --------- I---------------------------------------------- DI/SF-A:1989 EFFECTIVENESS CALCULATIONS ----------------------;1-/----------------------------------------- PROJECT: 5LJnl5TNE I o 1 L L ,4 GE 7 7HS Ug)p pU DSTANOARO FORM 8 J COMPLETED BY: s n e) t/a N DATE: -30�TZ Erosion Control C-Factor P-Factor Method Value Value Comment ! --------------------- I Slw----atk5 ------O.0 1 1.0 --------------------- Gre, rs Sri r17 4Fn+ -Tre, p remP. Crop 5�-YoLV 7341e5' ------------ MAJORI PS BASINI W ---- -1------ 7; A 7+� 1171W 75,9 77,6 SUB I BASINI -----1 7-Z 7-7 AREA -(Ac)- Z, $ 2.7,t 77, 17-410.5z� I I hl ; - 71�, G 7 0,30 ------ --------------- II/SF-8:1989 ' o,a ! CALCULATIONS ------------------------- I ------------------- Roa�is 0-ft4e- ITSTAE GRA,55 13a r= Gre and 1. 97 (5c'et:4 w/-rAt p.C,'r1i,,p) VA17a C =0-oA1 X0,4-1)+ 0.44)<0,67) 4- i,9?xa< -0Z,B= 0,33 I wT,� PF�c�r-oiz = o.8xo.8xo,� =a,3z� f 1v14h)ee5 1MProVChi en IrmMe4reAt"ei c�awrlsfr�a w! I 1�o act s D, Itl Rc Grass 6,3Ac WTDCFRcro�' = DA1 3K0,4P+19)6POUAJ0 -C.ZOL L p 4 a,3Xo,07, 4-0 3X0 , 45�3 WTD PrACTvbZ = 0,8 X0-6X0,8=6, too I�oG,:45 D .ZZhe- 0,10 &6 G✓clunc� o,ZOAc- GSQed Grvuhd w/' ►Vr,o if L"o.�1 x0.ZZ 4 o .1xo.0-7+ 0,ZYI 5 374 c er) 5.(w Z i; K. a K e- etv Cover) 81,0 oe- ' CONSTRUCTION SEQUENCE PROJECT: sy N 5 To N E U L LL AGE 7 STANDARD FORM C SEQUENCE. FOR 19 92, ONLY COMPLETED BY: (% L D DATE: — 3D Indicate by use of a bar line or symbols when erosion control measures will be installed. Major modifications to an approved schedule may require submitting a new schedule for approval by the City Engineer. YEAR MONTH Au6I SeQiOz-'rl kvi ac! I I I I I I I ---------------------------- OVERLOT GRADING -----------------------------------------------------------I LJT! L—rTY INSTALL�Tro WIND EROSION CONTROL Soil Roughing r f-----�' Perimeter Barrier Additional Barriers Vegetative Methods Soil Sealant I Other RAINFALL EROSION CONTROL STRUCTURAL: Sediment Trap/Basin Inlet Filters ✓_ I Straw Barriers ✓ (----} Silt Fence Barriers Sand Bags Bare Soil Preparation Contour Furrows Terracing I Asphalt/Concrete Paving ✓ �--- Other VEGETATIVE: Permanent Seed Planting Mulching/Sealant Temporary Seed Planting H ` Sod Installation.. Nettings/Mats/Blankets Other -• ----------------------------------------------------------------------------------------I STRUCTURES: INSTALLED BY Owe) C r ( MAINTAINED BY Ovuh C VEGETATION/MULCHING CONTRACTOR SGV1I�l fGl �" �Qr Lh 13u OeJCrS � DATE SUBMITTED — APPROVED BY CITY OF FORT COLLINS ON "II/SF-C:1989 1 9790S I oN CON7-R6 L * -r So gsTo�jC V I LLAC,E Fi,L r(A, DWN�25� �STI�'�1tiT� o� C©sT �, Co s T aF �Rd 51 Uo� CoN-rrRo�. /'(�Tt-1al�s GRAVEL FI L -r= E3, OAy 6 cry (BURIED) 80 If o L,CeZ C. 5sp/J1!lZ60 RY Gs o u N o .Ca v;E q;Z AcC 3 c�jA l�L-76 T 07-A L �Cos T 0FC-ry'5 unfiT P/e/cf. PoR SESD/NG i�-/4uLG4/NG .�V,-e �_ Q -F 7, To T,4L' o" Ly 4-. 2 Ac. MAX. n SE. !/ls-ry R& L A RdSR Co sT = s,3�8.�9 Co',7- n 150°1a =' 81'46801a S�cuRi�Y h��Q�iR�O o� ���468.18 P .� �d.,4�A