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Home My WebLink AboutDrainage Reports - 03/22/1994 (2)James H. Stewart and Associates, Inc. Consulting Engineers and Surveyors STORM DRAINAGE REPORT FOR LEMAY-HARMONY SPECIAL IMPROVEMENT DISTRICT #78 (OAK RIDGE PORTION) r 3 Q R < aA gQ F 3 OFFICE-214 NORTH HOWES • P.O. BOX 429 • FORT COLLINS, COLORADO 80522 • TELEPHONE 303/482-9331 FROM JAMES H. STEWART AND ASSOCIATES, INC. CONSULTING ENGINEERS James H. Stewart and Associates, Inc. 1 _, James H. Stewart and Associates, Inc. Consulting. Engineers and Surveyors Laboratory: 214 North Howes Street 301 Lincoln Court P.O. Box 429 - - P.C. Box 429 Fort Collins, Colorado 80522 - Fort Collins, Colorado 80522 (303)482-9331 - (303)4846309 STORM DRAINAGE REPORT -- FOR . LEMAY-HARMONY SPECIAL IMPROVEMENT.DISTRICT #78 (OAK RIDGE PORTION) INTRODUCTION: That.portion of the proposed Oak Ridge Subdivision which is to be included in the Lemay-Harmony Special Improvement District (S.I.D.) #78 is located in the West half of the Northwest 1/4 of Section 6, Township 6 North, Range 68 West of the.Sixth P.M. in the City of Fort Collins, Colorado. The site, is zoned mostly Business, with some Residential.. A primary reference is the McClelland and Mail_Creek Major Drainageway Plan, December 1980. In . this report, this study will be referred to as the McClelland Drainage Study. EXISTING DRAINAGE: The McClelland Thalweg moves through the North 1/4 of the proposed area in a Southeasterly direction (See Exhibit #1). Drainage moves toward the McClelland Thalweg South from Harmony and North from a mild ridge running East and West through the Rule property. From this same ridge, runoff moves South -to an.existing thalweg running East and West which is located approximately 500 feet North of the Oak Ridge South property line. Drain- age moves North to this thalweg from Mail Creek Ditch, which is located South of the Oak Ridge South property line (See Exhibit #1). _ i. PROPOSED SITE DRAINAGE:- 1: -Oak Ridge Business Park, First Filing. The Oak Ridge Business Park, First Filing, is shown as Phase 1 on Exhibit #1. Proposed drainage in this area is described in the Oak Ridge Business Park, First Filing, Storm Drainage Report and the reader is referred to this report. The inlets as shown on Exhibit #1 show size of opening in parentheses. Several changes in the original report have been made. Inlets A through 0 have been relabeled as follows: Inlet A = SDI-3 Inlet B = SDI-4 Inlet C = SDI-2 Inlet D = SDI-1 (SDI = Storm Drain Inlet) -1- 1 The inlets labeled SDI-1, SDI-2 and SDI-4 each receive a 10-year design flow of 2;O cfs. :The inlet SDI-4 has been increased to a 10-foot-long nlet'so-that it can receive runoff from the East- bound lanes of Harmony Road once curb and gutter.are.placed along Harmony. This additional flow from Harmony.equals 5.0 cfs. The total flow entering inlet SDI-3 is 7 cfs. The storm drain between SDI-2 and the outletiinto McClelland's Thalweg was increased from'a 21-inch to a.24-inch to handle the additional flow from Harmony Road. Everything else is the same.. as spelled out in the Oak Ridge Business Park, First Filing, "� Storm Drain Report. The reader is,referred to this report . 'for specifics. 2 Improvements to McClelland's Thalweg. McClelland's Thalweg,as it traverses through the Oak Ridge property, is intercepted by two streets, Oak Ridge Drive and Wheaton Drive. At Oak Ridge, the 10-year developed flow equals 59.0 cfs and is carried under the road by three 36-inch culverts. The two inlets, SDI-12 and SDI-13, receive runoff from the street. 'The two are connected to one another via a 15-inch line. Another 15-inch line exits SDI-13 and empties -into McClelland's Thalweg on the downstream side. Inlet SDI-12 receives 3.86 cfs and Inlet SDI-13-receives 2.51 cfs. The three 36-inch culverts have enough capacity to carry the 10-year combined channel and street flow which will. not surcharge the system. All of the 100-year fully - developed flow, which equals 171 cfs, will be carried under the road at Oak Ridge (i.e., no overtapping will occur). The.10-year developed flow to be carried under Wheaton is 90.0 cfs. This will require two 427inch-culverts. Two inlets, SDI-10 and SDI-11, receive .runoff from the street. The two are connected to one another.via a 15-inch line. Another 15-inch line exits SDI-10 and empties into McClelland's Thalweg on the downstream side. Inlet SDI-10 receives 3.63 cfs and Inlet SDI-11 receives 4.32 cfs. The 100-year fully -developed flow at Wheaton Drive equals 367 cfs. Of this.total, 214 cfs-will pass through the culverts, while.the re- maining 153 cfs will pass over the top of Wheaton Drive with a depth at the crown not exceeding six inches. The channel sections for the improved McClelland Thalweg were designed to carry 100-year flows under fully -developed conditions. The channel sections vary as the thalweg moves across the Oak Ridge property. The locations of varying channel sections are shown in Exhibit #1 and the section details are shown on Exhibit #2. These sections are labeled A -A, B-B and C-C. The off -site, 100-year fully -developed flow from McClelland's basin, after detention, equals 55 cfs. This flow enters the -2- James H. Stewart and Associates, Inc. I 1 proposed Oak Ridge site via an -existing 27-inch by 44-inch arch pipe under Lemay and Harmony. Channel Section A -A is designed to handle the off -site flow of 55 cfs. As the thalweg moves from Harmony to Oak Ridge Drive, the on - site runoff equals 116 cfs (A = 15.6.acres, C = 0.85 acres). :This flow is added to the 55.0 cfs off -site flow and equals a total of 171 cfs.. Channel Section B-B is designed to handle this total flow. Similarly, the thalweg continues"from Oak Ridge Drive to Wheaton Drive, accumulating additional runoff from a total area of 42.0 acres, which includes most of Oak Ridge Business Park, First Filing. The total flow, which includes the 55.0 cfs off -site flow, equals 367 cfs. Section C-C was - designed to handle this total flow. 30'-Storm Drain Design from Rule Drive to Keenland Drive. The storm drain system which carries the runoff from areas A, B, C, D and E is designed to carry 10-year fully -developed flows which will empty into the existing thalweg, located just East of the Wheaton - Keenland intersection. (See Exhibit #1). Inlet SDI-9, located on the Northwest corner of Wheaton and Rule, has a 24-inch stub -out which receives a - flow of 25.5 cfs and is transported South down Wheaton via a 24-.inch storm drain until it is intercepted by runoff from Area B. At this point, the combined 10-year fully -developed flow from Areasz.A and B equals 48 cfs, and the storm drain in- creases to a 30-inch pipe, which goes all the way to the manhole at the intersection of Wheaton and Keenland. This manhole also receives runoff from half the street of Rule Drive and Keenland.Drive, and that portion of Wheaton between Rule and Keenland. This 10-year flow equals 5.7 cfs and empties into Inlet SDI-8 (See Exhibit #1). A 15-inch line exits SDI-8 and tapsdirectly into the side of the-34-inch..by 53-inch oval pipe which carries runoff -from Open Channel "A". Additional runoff enters the same manhole via .a 34-inch by 53-inch elliptical pipe. This is accumulative runoff from Area C and 240 off -site acres West of Lemay Avenue. Three 30-inch culverts (de termined by others) carry a 10-year existing -condition flow of 53 cfs-from off -site under Lemay and empty into Open Channel "A". Open Channel "A" also.carries 10-year fully -developed runoff from Area C which, when combined with the off -site flow, equals a total . of 71 cfs. This total flow is conveyed to the manhole at the intersection of Wheaton and Keenland Drive via .the 34-inch by .53-inch elliptical pipe. The combined 10-year flow which exits this manhole via a 38-inch by 60-inch elliptical pipe equals 104 cfs. This flow then empties into the existing thalweg East of the Wheaton-Keenland Drive intersection. -3- James H. Stewart and Associates, Inc. ,b 5�- Inlets SDI-6 and SDI-7, located on the Northeast corner of Wheaton and Keenland, receive a total flow of 8.4 cfs (4.2 cfs each) from Area D for 10-year fully -developed condi ions This flow is conveyed via a 15-inch and 18-inch pipe t D - which is located on the South side of Keenland. Inlet SDI- receives 4.1 cfs from Area E for 10-year fully -developed con i ions. The total 10-year fully -developed flow from Areas D and E equals 11.7 cfs and empties into the existing thalweg East of the Wheaton-Keenland intersection via an 18-inch pipe. The runoff for the remainder of land between Area E and the South property line of Oak Ridge will find its way overland to this thalweg. Major Storm Design from Rule Drive to Keenland Drive. Open Channel "A" is designed to carry the 100-year off -site existing -condition flow West of Lemay and the 100-year fully - developed flow from half of Area C. This total flow equals 125 cfs. See Exhibit #3 for a section detail of Open Channel "A". The portion of 125 cfs that is not taken by the storm drain system will spill over the intersection into the existing thalweg, located on the East side of the Wheaton - Keenland intersection. Runoff from Areas A, B and half of C under 100-year fully - developed conditions finds its way down Wheaton Drive, where it is carried to and through the intersection of Wheaton and Keenland into the existing thalweg East of this intersection. The 100- year runoff for fully -developed conditions from Area D spills over the intersection after the storm drain system reaches its capacity. The 100-year total flow at the entrance to the exist- ing thalweg just East of the Wheaton - Keenland intersection is 300 cfs. Of this total, 116 cfs will pass through the culvert, while the remaining 184 cfs will overtap the Wheaton - Keenland intersection with a depth at the crown not exceeding six inches. Designed by Guy F. McCabe Written by DGn J. McClelland -4- James H. Stewart and Associates, Inc. '3 r o, _ d� t t l t l m ? lD m ��CNV I 7V54,O l` car s �u �; ) `� > � �� , �. � � �• � � •3 � �`� "� � � � t �1' ems.._ , � _ �� _ . _ _ _ Ar �1 7 / I tA`7t/r//.} No Text No Text