DRAINAGE STUDY. 645 Beard Creek Trail Lot 8, Cordillera Valley Club Filing No. 1 Eagle County, Colorado. November 25, Project No.

Transcription

1 DRAINAGE STUDY 645 Beard Creek Trail Lot 8, Cordillera Valley Club Filing No. 1 Eagle County, Colorado November 25, 2014 Project No Prepared for Mr. Robert Myers Caribbean Group P.O. Box N 1968 Nassau, Bahamas P.O. Box 2837, Edwards, CO Tel (970)

2 DRAINAGE STUDY TABLE OF CONTENTS: SCOPE OF STUDY SITE DESCRIPTION RECORDS RESEARCH DRAINAGE BASIN DRAINAGE CRITERIA FINDINGS AND RECOMMENDATIONS LIMITATIONS...6 APPENDIX A WinTR-55 STUDY SOILS STUDY RAINFALL INTENSITY LKP Engineering, Inc.

3 DRAINAGE STUDY SCOPE OF STUDY This report represents the results of our drainage study, which incorporates a site reconnaissance, reviews of existing documents and records, calculations, and analysis of the information. The purpose of the study was to evaluate the existing conditions of the site with respect to the runoff from 2 and 100-year storm event, to verify the capacity of the existing 30-inch culvert, and to provide design recommendations for a drainage swale. SITE DESCRIPTION The site is located at 645 Beard Creek Trail, Lot 8, Cordillera Valley Club Filing No.1, Eagle County, Colorado. It is on the uphill side of the road, and the topography of the site is steep to moderate sloping to the south. The lot is between approximate elevations of 7400 and 7460 feet above sea level. The vegetation consisted of sage brush, juniper and sparse wild grass. On the west side of the property is Deadhorse Gulch with a watershed of about 138 acres. The Deadhorse Gulch is crossing under Beard Creek Trail, near the southwest corner of the lot, through an existing 30-inch, corrugated plastic culvert. Approximately the west half of the lot is within the Deadhorse Gulch Watershed. There are several dry gulches running through the lot and the watershed area. Two dry gulches run from the northeast corner of the lot toward the proposed building site. There is another dry gulch running along the eastern property line. This gulch is discharging into a catch basin with a 12-inch outlet pipe across the southwest corner of the driveway on Lot 7. Part of this gulch also runs in very close proximity to the base of the retaining wall supporting the proposed driveway and turnout on Lot 7. LKP Engineering, Inc. -1-

4 DRAINAGE STUDY RECORDS RESEARCH For the drainage study we used the following resources: 1. Topographic survey, ed by Lee Lechner, registered land surveyor. 2. Site plan, ed by Stephanie Lord-Johnson LEED AP, with Berglund Architects, LLC. 3. NOAA Atlas 2, Volume III-Colorado, for the rainfall intensities in the Western United States. 4. Rainfall intensity-duration-frequency curves for the Edwards area. 5. Soil Survey of the Aspen-Gypsum Area of Garfield County from the US Department of Agriculture Soil Conservation Service. 6. USDA NRCS, TR55 Software 7. Rational Method Calculations 8. Manning s Open Channel and Pipe Flow Calculator 9. Partial field site reconnaissance (September 18, October 31, and November 2, 2014). 10. Eagle County GIS Department topography. DRAINAGE BASIN The proposed development is within the Eagle River Drainage basin. The watershed area for Deadhorse Gulch is approximately 138 acres. The watershed is in a plume shape with a maximum elevation of 8410 feet above sea level and 7386 feet above sea level at the discharge point. The Deadhorse Gulch had water running in it during our site visits, and appears to be a live, mountain stream. At the time of our visit, the gulch ditch had 2-4 inches of water depth. The section that we walked, was about 600 feet above the outlet, and within this area, the stream channel had irregular width ranging from one to four feet, waterfalls and pools, and it was winding through the juniper forest. The ditch channel was for the most part rectangular with 12-inch sides, while the banks had variable heights and slopes, with an average of one to one side slope. Vegetation cover of the drainage basin consists of juniper forest with sage brush on the open areas, and sparse grass. There was also a lot of rock over the area. DRAINAGE CRITERIA The USDA (United States Department of Agriculture) NRCS ( Natural Resources Conservation Service) software WinTR-55 Small Watershed Hydrology was used for the LKP Engineering, Inc. -2-

5 DRAINAGE STUDY calculations of the watershed hydrology. The rational method, for small watersheds of up to 200 acres, was used for the calculations of watershed for the drainage swale. The design storm events analyzed were the 2, 10, 50, and 100-year storms. FINDINGS AND RECOMMENDATIONS The Win TR-55 software was used to calculate the flow from the Deadhorse Gulch Watershed. Following is the Watershed Peak Flow Table (the full report is attached): Project: Beard Creek Trail Eagle County, Colorado Watershed Peak Table Sub-Area Peak Flow by Rainfall Return Period or Reach 2-Yr 10-Yr 50-Yr 100-Yr Identifier (cfs) (cfs) (cfs) (cfs) SUBAREAS Tract REACHES OUTLET Based on this study and the condition of the watershed at present time, the peak flow from a 100-year storm event is 129 cfs. The existing 30-inch culvert was corrugated plastic pipe with smooth inner walls. Based on the survey information by lee Lechner, the pipe is 119 feet long and it has a slope of 15.2%. The capacity of the existing 30-inch culvert was calculated based on the Manning s Pipe Formula. Following are the calculations: LKP Engineering, Inc. -3-

6 DRAINAGE STUDY Existing 30-inch Culvert CPP with Smooth Inner Wall INPUT DATA: Pipe diameter D: 2.5 ft Flow depth y: 2.4 ft Bottom slope S: ft/ft Manning's n: INTERMEDIATE CALCS: Constant k: Flow area A: ft2 Wetted perimeter P: ft Hydraulic radius R: ft Relative depth y/d: Froude number [based on y]: OUTPUT: Discharge Q: cfs Flow velocity V: fps Based on the above calculations, the peak flow from the watershed is 129 cfs and the capacity of the existing 30-inch culvert is 186 cfs. The existing culvert, for the present time and conditions, has a sufficient capacity to transmit the 100-year peak flow from the Deadhorse Gulch watershed. With the proposed development on the lot, a driveway crossing is proposed over the Deadhorse channel. On the architectural site/grading plan they show about 40-foot extension to the existing 30-inch culvert for this purpose. At the inlet of the culvert extension, we recommend an end section with a trash rack to prevent debris and rocks from blocking the culvert. We also recommend that a new storm manhole with an inlet grate and steps for maintenance be constructed at the junction of the existing culvert with the proposed new culvert. The construction of the culvert will serve the purpose for future maintenance of the culvert and as an inlet for the runoff from the proposed new driveway. At the base of the driveway we also recommend a 4-foot concrete pan with a two-inch depth. The concrete pan will extend from the base of the driveway to the inlet at the proposed new, storm manhole. LKP Engineering, Inc. -4-

7 DRAINAGE STUDY Drainage above the Proposed Residence The watershed above the proposed drainage swale is 1.72 acres. The peak flow for the 100-year storm event for the watershed of the proposed drainage swale was calculated by the Rational method: Q=CiA Where: Q = Peak Discharge (cfs) C = Runoff coefficient, a ration of runoff to rainfall I = Average rainfall intensity for a duration equal to the time of concentration, for a selected return period (in/hr) A = Watershed drainage area (ac) The appended rainfall intensity curves for Edwards, Eagle County, were used in the calculations. Runoff coefficient of 0.5 was used in the calculations for a steep watershed with sage brush and juniper type of vegetation cover. Following are the summary results for the 100-year storm event: Watershed above the Diversion Drainage Swale INPUT DATA: Runoff coefficient C :.05 Rainfall intensity I : 5.3 in hr-1 Drainage area A : 1.72 ac OUTPUT: Peak discharge Qp : 4.60 cfs Based on the peak discharge of 4.6 cfs a drainage swale cross section was calculated with a 1-foot bottom, 1H:1V slope sides and two feet total depth. The swale will be lined with a pond liner and rock. The purpose of the drainage swale is to divert the uphill runoff and to protect the proposed residence. The backfill material and the bottom of the swale will be compacted before the placement of the pond liner and the rocks, and the disturbed surrounding areas will be re-vegetated to reduce the potential for erosion. In addition to the construction of the proposed drainage swale, the two dry LKP Engineering, Inc. -5-

8 DRAINAGE STUDY gulches in the northeast corner of the lot will be incorporated into the drainage swale and any parts of the dry gulches remaining below the swale will be filled in and revegetated. Watershed above the existing dry gulch and 12-inch culvert on the east side of the property. Drainage study of this watershed is not part of our scope of work. The dry gulch does not originate or discharge on Lot 8. The existing dry gulch and the structures below were not evaluated. We understand that erosion of the channel is an ongoing event. In order to reduce the erosion of the natural, drainage channel, we propose (see the drainage plan) that the dry gulch be reconstructed with a pond liner and lined with rip-rap. In addition, and this is at the discretion of the homeowner, we recommend a concrete apron around the existing catch basin inlet, which will also reduce the potential of erosion around the inlet and guide the water toward it. The above recommendations are standard practice for erosion control and can and should be evaluated by the consultant for Lot 7. Maintenance For the continuous performance of the proposed drainage improvements to the site a regular maintenance must be scheduled. As a minimum, in spring and fall the inlet to the 30-inch culvert and the manhole inlet grate must be inspected and cleaned as necessary. Additional maintenance after heavy storms should be done as well. At the same time the drainage swales should be observed and cleaned from debris and sediment. LIMITATIONS The above report has been prepared for the exclusive use of the Lisa and Robert Myers for the development their property at 645 Beard Creek Trail in the Cordillera Valley Club, Eagle County, Colorado. The study is limited to the information provided and the data available at the time of our study. This report has been prepared according to locally accepted professional engineering standards at this time. There is no other warranty either expressed or implied. If you have any questions, please do not hesitate to call. Sincerely, LKP Engineering, Inc. Luiza Petrovska, PE Enclosure C:\Users\Luiza\Documents\_WPX4\ Myers\ dr_st.wpd LKP Engineering, Inc. -6-

9 DRAINAGE STUDY APPENDIX A LKP Engineering, Inc.

10 WinTR-55 Current Data Description --- Identification Data --- User: LP Date: 11/4/2014 Project: Units: English SubTitle: 645 Beard CReek Trail Areal Units: Acres State: Colorado County: Eagle Filename: C:\Users\Luiza\Documents\_WPX4\ Myers\tr55study.w Sub-Area Data --- Name Description Reach Area(ac) RCN Tc Tract 1 Existing Land Use Outlet Total area: 138 (ac) --- Storm Data -- Rainfall Depth by Rainfall Return Period 2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr (in) (in) (in) (in) (in) (in) (in) Storm Data Source: User-provided custom storm data Rainfall Distribution Type: Type II Dimensionless Unit Hydrograph: <standard> WinTR-55, Version Page 1 11/4/ :23:41 PM

11 LP Beard CReek Trail Eagle County, Colorado Storm Data Rainfall Depth by Rainfall Return Period 2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr (in) (in) (in) (in) (in) (in) (in) Storm Data Source: User-provided custom storm data Rainfall Distribution Type: Type II Dimensionless Unit Hydrograph: <standard> WinTR-55, Version Page 1 11/4/ :23:41 PM

12 LP Beard CReek Trail Eagle County, Colorado Watershed Peak Table Sub-Area Peak Flow by Rainfall Return Period or Reach 2-Yr 10-Yr 50-Yr 100-Yr Identifier (cfs) (cfs) (cfs) (cfs) SUBAREAS Tract REACHES OUTLET WinTR-55, Version Page 1 11/4/ :23:41 PM

13 LP Beard CReek Trail Eagle County, Colorado Hydrograph Peak/Peak Time Table Sub-Area Peak Flow and Peak Time (hr) by Rainfall Return Period or Reach 2-Yr 10-Yr 50-Yr 100-Yr Identifier (cfs) (cfs) (cfs) (cfs) (hr) (hr) (hr) (hr) SUBAREAS Tract REACHES OUTLET WinTR-55, Version Page 1 11/4/ :23:41 PM

14 LP Beard CReek Trail Eagle County, Colorado Sub-Area Summary Table Sub-Area Drainage Time of Curve Receiving Sub-Area Identifier Area Concentration Number Reach Description (ac) (hr) Tract Outlet Existing Land Use Total Area: 138 (ac) WinTR-55, Version Page 1 11/4/ :23:41 PM

15 LP Beard CReek Trail Eagle County, Colorado Sub-Area Time of Concentration Details Sub-Area Flow Mannings's End Wetted Travel Identifier/ Length Slope n Area Perimeter Velocity Time (ft) (ft/ft) (sq ft) (ft) (ft/sec) (hr) Tract 1 SHEET SHALLOW CHANNEL CHANNEL Time of Concentration.159 ======== WinTR-55, Version Page 1 11/4/ :23:41 PM

16 LP Beard CReek Trail Eagle County, Colorado Sub-Area Land Use and Curve Number Details Sub-Area Hydrologic Sub-Area Curve Identifier Land Use Soil Area Number Group (ac) Tract 1 Pinyon - juniper (fair) D Desert shrub (fair) A Desert shrub (fair) B Total Area / Weighted Curve Number === == WinTR-55, Version Page 1 11/4/ :23:41 PM

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34 Precipitation Frequency Data Server Page 1 of 4 11/4/2014 NOAA Atlas 14, Volume 8, Version 2 Location name: Edwards, Colorado, US* Latitude: , Longitude: Elevation: 8384 ft* * source: Google Maps POINT PRECIPITATION FREQUENCY ESTIMATES Sanja Perica, Deborah Martin, Sandra Pavlovic, Ishani Roy, Michael St. Laurent, Carl Trypaluk, Dale Unruh, Michael Yekta, Geoffery Bonnin NOAA, National Weather Service, Silver Spring, Maryland PF_tabular PF_graphical Maps_&_aerials Duration 5-min 10-min 15-min 30-min 60-min 2-hr 3-hr 6-hr 12-hr 24-hr 2-day 3-day 4-day 7-day 10-day 20-day 30-day 45-day 60-day PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches) 1 Average recurrence interval (years) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1.08 ( ) 1.34 ( ) 1.52 ( ) 1.67 ( ) 2.09 ( ) 2.44 ( ) 3.41 ( ) 4.25 ( ) 5.35 ( ) 6.34 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1.24 ( ) 1.52 ( ) 1.73 ( ) 1.91 ( ) 2.34 ( ) 2.71 ( ) 3.77 ( ) 4.70 ( ) 5.95 ( ) 7.08 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1.22 ( ) 1.53 ( ) 1.84 ( ) 2.09 ( ) 2.31 ( ) 2.78 ( ) 3.18 ( ) 4.38 ( ) 5.46 ( ) 6.94 ( ) 8.26 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1.08 ( ) 1.41 ( ) 1.78 ( ) 2.12 ( ) 2.42 ( ) 2.66 ( ) 3.17 ( ) 3.59 ( ) 4.91 ( ) 6.12 ( ) 7.75 ( ) 9.22 ( ) ( ) ( ) ( ) ( ) 1.02 ( ) 1.11 ( ) 1.14 ( ) 1.31 ( ) 1.70 ( ) 2.14 ( ) 2.53 ( ) 2.89 ( ) 3.17 ( ) 3.73 ( ) 4.20 ( ) 5.68 ( ) 7.04 ( ) 8.87 ( ) 10.5 ( ) ( ) ( ) ( ) 1.09 ( ) 1.19 ( ) 1.30 ( ) 1.33 ( ) 1.50 ( ) 1.94 ( ) 2.44 ( ) 2.88 ( ) 3.28 ( ) 3.59 ( ) 4.19 ( ) 4.69 ( ) 6.31 ( ) 7.78 ( ) 9.74 ( ) 11.5 ( ) ( ) ( ) 1.05 ( ) 1.25 ( ) 1.38 ( ) 1.50 ( ) 1.53 ( ) 1.70 ( ) 2.19 ( ) 2.75 ( ) 3.25 ( ) 3.68 ( ) 4.02 ( ) 4.67 ( ) 5.21 ( ) 6.96 ( ) 8.54 ( ) 10.6 ( ) 12.4 ( ) ( ) ( ) 1.17 ( ) 1.42 ( ) 1.57 ( ) 1.72 ( ) 1.75 ( ) 1.93 ( ) 2.45 ( ) 3.08 ( ) 3.64 ( ) 4.12 ( ) 4.49 ( ) 5.18 ( ) 5.76 ( ) 7.65 ( ) 9.32 ( ) 11.5 ( ) 13.3 ( ) ( ) 1.07 ( ) 1.31 ( ) 1.64 ( ) 1.84 ( ) 2.03 ( ) 2.07 ( ) 2.25 ( ) 2.83 ( ) 3.53 ( ) 4.19 ( ) 4.73 ( ) 5.13 ( ) 5.88 ( ) 6.53 ( ) 8.61 ( ) 10.4 ( ) 12.6 ( ) 14.5 ( ) ( ) 1.16 ( ) 1.41 ( ) 1.81 ( ) 2.05 ( ) 2.29 ( ) 2.33 ( ) 2.52 ( ) 3.12 ( ) 3.89 ( ) 4.64 ( ) 5.21 ( ) 5.64 ( ) 6.44 ( ) 7.13 ( ) 9.36 ( ) 11.2 ( ) 13.5 ( ) 15.4 ( ) 1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top PF graphical

35 Precipitation Frequency Data Server Page 2 of 4 11/4/2014 Back to Top Maps & aerials Small scale terrain 50 km Map data Report 2014 a map Google error

36 Precipitation Frequency Data Server Page 3 of 4 11/4/2014 Large scale terrain 2 km Map data 2014 Google Report a m ap error Large scale map 2 km Map data 2014 Google Report a m ap error Large scale aerial 2 km Im agery 2014 Report TerraM a map etrics error Back to Top US Department of Commerce National Oceanic and Atmospheric Administration National Weather Service Office of Hydrologic Development 1325 East West Highway Silver Spring, MD 20910

37 Precipitation Frequency Data Server Page 4 of 4 11/4/2014 Questions?: HDSC.Questions@noaa.gov Disclaimer