Drainage Study Research

Clark County

City of Las Vegas

  • City of Las Vegas Public Works, 495 S Main St, Las Vegas NV 89101, 702-229-6276, publicworks@lasvegasnevada.gov
  • Peter Jackson, pjackson@lasvegasnevada.gov
  • Albert Y. Sung, Project Engineer, 702-229-6541, ysung@lasvegasnevada.gov
    • 333 N Rancho Dr, 7th floor, Las Vegas NV 89106
  • Mike Janssen, Public Works Director, 702-229-6272
  • Offsite Improvements
    • Michael Cunningham in Building & Safety Department, 702-229-2002
  • Drainage Studies
    • Oh-Sang Kwon in Flood Control Section, 702-229-1815, okwon@lasvegasnevada.gov
  • Traffic Studies
    • Rick Schroder in Transportation Section, 702-229-2452
  • Records Research

Schedule

Grading Plan Notes

Submittal

  • Inserts - Transmittal Letter (optional)
  • 2 copies of Drainage Study - bound
  • Addendum Only - copy of original redlines. Use a highlighter to mark redlines once changes have been made to the grading plan, can also write comments for the reviewer.
  • Need a Check from the Developer for review fees - not required on first addendum, only for initial review, 2nd, 3rd, 4th etc reviews
  • Plans
    • Cover
    • General Notes
    • Grading Plan
    • Exclude (not part of drainage study)
      • Horizontal Control
      • Utility
    • Must be stamped, signed and dated
    • ok to say “NOT FOR CONSTRUCTION” over the PE stamp
    • Drainage Signature Block on all grading plan sheets
    • CCPW Development Review Acceptance of Plans for Filing signature block on all grading and plan/profile sheets

Supplement to Drainage Study

Project Folder

Clark County Technical Drainage Study

  • loose inserts
    • Transmittal letter
    • Drainage Study Submittal Sheet
  • Bound Report

01_-Title Page

  • Acetate clear cover
  • 01-cover - cardstock
  • Project Name, Type of Study, Study Date
  • Preparer's Name, Seal and Signature

01A-Standard Form 1

01B-Standard Form 2

  • (only on initial submittal) Drainage Submittal Checklist
    • 04-Table of Contents
    • 05-Cover with Preparer's Name, Seal, and Signature
    • 10-Introduction
      • 11-Standard Forms 1 and 2
      • 12-Table of Contents
      • 13-Description of Project
      • 14-Existing Site Conditions
      • 15-General Location Map (8.5“x11”)
    • 20-Existing and Proposed Hydrology/Hydraulics
      • 21-Discuss existing and proposed and future/ultimate drainage basin boundaries
      • 22-Present existing and proposed minor and major storm flow calculations (if required)
      • 23-Discuss existing drainage patterns and areas of inundation (if applicable)

03_-DrainageBasinDescription

03A-Offsite Drainage Description

  • 1-Discuss off-site flows which enter property at the following discrete points
  • 2-Discuss off-site flows which enter property at non-discrete points
  • 3-Discuss existing and proposed land use types and level of development in upstream basin
  • 4-Hydrologic soil groups, vegetation and slope
  • 5-Natural and manmade conveyances in the watershed

03B-Onsite Drainage Description

  • 1-Discuss historic on-site drainage patterns of the property (flow directions through site and at property line)
  • 2-Discuss historic drainage patterns of upstream runoff
  • 3-Discuss historic discharge points at downstream property lines

03C-Master Planning Information

  • 1-Identify currently adopted master plans which include the subject site
  • 2-Discuss proposed Master Plan Flood Control Facilities on subject site
  • 3-Discuss upstream master Plan Flood Control Facilities which would affect runoff on subject site
03C-a-MPU Facility Map
03C-b-MPU Facility Table Summary
  • CCRFCD MPU Facility Inventory
03C-c-MPU Watershed Map

03D-Floodplain Information

  • 1-Identify all FEMA regulated floodplains which overlay on the subject site
  • 2-Identify all calculated floodplains, including a proposed conditions or “with-project” floodplain

03E-Previous Drainage Studies

  • Identify any previous drainage studies for the site
  • Identify any previous drainage studies which affect the site

04_-Proposed Drainage Facilities

04A-General Description

  • 1-Discuss proposed Local (On-Site) Drainage System plan and layout
  • 2-Discuss proposed Local (Off-Site) Drainage System plan from the Local (On-Site) Drainage System to the Regional Flood Control System
  • 3-Discuss proposed Regional Flood Control System design (only where the Regional Flood Control System passes through the subject site)

04B-Compliance with Regulations and Adopted Plans

  • 1-Discuss compliance with all Master Planned Flood Control Facilities (as applicable) and discuss all proposed deviations from the adopted Master Plans
  • 2-Discuss compliance with FEMA floodplain regulations and all proposed modifications to or verifications of the FEMA regulated floodplain through the subject site
  • 3-Discuss compliance with rules and regulations for developments on alluvial fans (if applicable)
  • 4-Discuss compliance with previously approved drainage studies for the subject site
  • 5-Discuss compliance with BMPs as discussed in Section 1500
  • 6-Identify individually all requests for variances from the requirements of the drainage criteria and variances from the local entities' development code
  • 7-Discuss compliance with Uniform Regulations
  • 8-Discuss compliance with the MANUAL

04C-Hydrologic Analyses

  • Hydrologic analyses shall be completed for the following conditions. Calculations for all conditions shall be bound in the report:
  • 1-Existing offsite and onsite
  • 2-Existing offsite and developed onsite (Interim Condition)
  • 3-Developed offsite and onsite (Future Developed Condition)
  • 4-Design rainfall computation discussion
  • 5-Design runoff computation discussion
Curve Number
  • Curve Number Calculations Jones/Maule Existing Conditions
    • (Drainage Study 03-15868 Jones Maule DS)
  • HCDDM Runoff Curve Numbers 1 of 4
  • HCDDM Runoff Curve Numbers 2 of 4
  • HCDDM Runoff Curve Numbers 3 of 4
  • HCDDM Runoff Curve Numbers 4 of 4
  • 6-Discuss peak flow rates from off-site areas and facilities
  • 7-Discuss flow split areas and analysis
  • 8-Hydrologic parameters
Time of Concentration and HEC-1 Input
  • Rick Engineering - Les Hopper/Andrew Bencini
    • RICK Time of Concentration
  • City of Las Vegas - Oh-Sang
    • City of Las Vegas Time of Concentration
  • 9-Routing schematic
  • 10-Calculations for parking lots and Low Impact Development LID impervious areas (if required) per section 1502.3

04D-Facility Design Calculations

  • 1-Discuss design calculations for the Proposed Drainage System
    • Street flow calculations
    • Storm sewer, inlets, and ditch flow calculations
    • Channel and culvert flow calculations
    • Other hydraulic structure flow calculations
    • Detention storage and outlet design calculations
    • BMP design calculations for parking lots and LIDs (if required)
  • 2-Discuss design calculations for the Local (Off-site) Drainage System
  • 3-Discuss Floodplain/Floodway calculations as related to FEMA requirements
  • 4-Discuss maintenance access and potential maintenance requirements. Provide maintenance procedures for privately maintained facilities, with projected annual maintenance costs for incorporation into homeowners association
  • 5-Discuss easement requirements for the proposed drainage facilities
  • 6-Discuss phasing of all drainage facilities

05_-Conclusions

  • 05A-Compliance with Drainage Laws
  • 05B-Compliance with Master Plans
  • 05C-Compliance with Federal Emergency Management Agency (FEMA) (if applicable)
  • 05D-Compliance with MANUAL
  • 05E-Compliance with REGULATIONS
    • Ability to provide emergency all weather access
  • 05F-Effectiveness of Proposed Drainage Facilities to Control Storm Runoff
  • 05G-Impact of Proposed Development on Off-site Property and Facilities

06_-References

  • Provide references for all drainage reports, plans and technical information used in preparing the drainage report

07_-Appendices

07A-HydrologicComputation

  • 1-Watershed boundaries
  • 2-Soils information
  • 3-Landuse information
07A-4a-Design rainfall calculations
07A-4b-6hr Reduction Factor
  • CCRFCD Drainage Design Manual Table 502
07A-4c-6hr Storm Distribution
  • CCRFCD Drainage Design Manual Table 503
07A-4d-Depth-Area Reduction Factor
  • CCRFCD Drainage Design Manual Table 505
  • 5-Basin parameter calculations
  • 6-Routing schematic
  • 7-Runoff calculations at design points
    • Minor and major storm flows
    • Flows for historic and fully developed basin conditions
  • 8-Hydrographs at property line discharge points, when appropriate
  • 9-Input data listing for all computerized hydrologic calculations, maps with all parameters
07A-9a-HEC-1 Existing
  • HEC-1 Input - Existing

07B-HydraulicCalculations

  • 1-Street and ditch capacities
  • 2-Inlet and storm capacities (including Energy Grade Line EGL and Hydraulic Grade Line HGL calculations), with inlet and outlet condition assumptions
  • 3-Channel and culvert capacities
  • 4-Floodplain/Floodway calculations
  • 5-Detention area/storage/discharge rating curves and calculations
  • 6-BMP hydraulic capacities
  • 7-Input data listing for all computerized hydraulic calculations
  • 8-Plots of all cross sections
  • 9-Map with cross section locations
  • 44-Discuss effect of development on adjacent properties
    • 44.1-Flow rates
    • 44.2-Discharge location
    • 44.3-Discharge velocity
    • 44.4-Inundation Limits
    • 44.5-Summary table for II and III
    • 44.6-List of facilities required
  • 45-Response to Comments (Addendum 01)
  • 50-Exhibits
  • 51-Drainage Plan
  • 52-Watershed Maps
  • 53-Cross Section Location Maps
  • 55-Reference Studies
  • 60-Calculations Appendix - Runoff calculations (existing and proposed)
  • 61-Standard Form 4
  • 61-HEC1
  • 63-Street and drainage facility capacity calculations, existing and proposed flood limit calculations
  • 67-Inlet Calculation
  • 68-Detention calculations
  • 90-Grading Plan
  • 91-Grading Plan initial
  • 92-Grading Plan redlines
  • 93-Grading Plan redlines with comments
  • 94-Grading Plan addendum 01
  • 10×13 Envelope to hold plans, cut top and top right corner off
  • 50-References
  • 60-Figures
  • 61-Vicinity Map
  • 62-Assessor's Parcel Map
  • 63-FEMA Flood Insurance Rate Map
  • 64-Regional Flood Control Facilities Map
  • 65-Regional Flood Control Land Use Map
  • 66-Existing Condition Drainage Basin Exhibit
  • 67-Developed Condition Drainage Basin Exhibit
  • 68-Future Condition Drainage Basin Exhibit
  • Blue plastic backcover
  • Acetate clear cover
  • plan inserts
  • drainage basin maps
  • grading plan redlines
  • redlines with comments
  • updated grading plan

References

NDOT

  • Cover sheet must be stamped and signed
  • Standard Form 1 must be stamped and signed
  • submit to Dave Facemyer (702-385-6510, dfacemyer@dot.state.nv.us) in Building A at 123 E. Washington Ave. He then mails it to Carson City for review.
    • Need a CD copy of the drainage study. Can also email a copy to Dave (not sure if he likes this)
    • Only need 1 hard copy submitted to Dave Facemyer.
  • Las Vegas Permits - lvpermits@dot.state.nv.us

Drainage Study Submittal Checklist

  • Regional Flood Control District - Standard Form 2 in Hydrologic Criteria and Drainage Design Manual - Drainage Submittal Checklist
  • General Requirement
    • Standard Form 1 with engineer's stamp and signature
    • Standard Form 2 checklist
    • Standard Form 4
    • Drainage Plan (36“x24”) two copies
    • Notarized letter from adjacent property owner(s) allowing off-site grading or discharge
  • Maps and Exhibits
    • Flood Insurance Rate Map (FIRM) with site delineated
    • Master Plan Update Figure (F-x) for Flood Control Facilities and Environmental areas with site delineated
      • RFCD Master Plan Update - Markup using Adobe Acrobat
    • Off-site drainage basin maps for existing, interim, and future conditions showing the existing topography, basin boundaries, concentration points, and storm flows in cfs.
    • On-site drainage basin maps for existing and proposed conditions showing the existing topography, basin boundaries, concentration points, and on-site and off-site flows in cfs.
    • Vicinity Map with local and major cross streets identified and a north arrow.
  • Drainage Plan
  1. Sheet size 36”x24“ sealed by a registered engineer in the State of Nevada
  2. Minimum scale 1”=60'
  3. Project name
  4. Vicinity Map with local and major cross streets
  5. Revision box
  6. North arrow and bar scale
  7. Engineer's address and phone number
  8. Elevation datum and benchmark
  9. Legend for symbols and abbreviations
  10. Cut/fill scarps, where applicable
  11. Street names with longitudinal slopes/grades and right-of-way widths
  12. Proposed future and existing spot grades at top of curbs (TC) and street centerline crowns at lot lines, grade breaks, and along curb returns on both sides of the street
  13. Existing contours encompassing the site and 100 feet beyond with spot elevations for important locations, where appropriate.
  14. Minimum finish floor elevations with top of curb (TC) elevations at upstream end of lot.
  15. Proposed typical street sections
  16. Streets with off-set crowns
  17. Proposed contours or spot elevations in sufficient detail to exhibit intended drainage patterns and slopes
  18. Property lines
  19. Right-of-way lines and widths, existing and proposed
  20. Existing improvements and their elevations
  21. Delineation of proposed on-site drainage basins indicating area and 10-year and 100-year storm peak flows at basin concentration points
  22. Concentration points and drainage flow direction with Storm Flowrate, Q100 and Velocity, V100 and Depth, D100 in streets.
  23. Cumulative flows, velocity, and direction of flow at upstream and downstream ends of site for the 10-year and 100-year flows
  24. Location and cross-section of street capacity calculations
  25. Cross-sectional detail for channels, including cutoff wall locations
  26. Existing and proposed drainage facilities, appurtenances, and connections (i.e., sidewalk, ditches, swales, storm drain systems, unimproved and improved channels, and culverts, etc.) stating size, material, shape, and slope with plan and profile and HGL calculations.
  27. Existing and proposed drainage easements and width shown with sufficient detail. A cross sectional detail must be provided that shows appropriate lining and reinforcement
  28. Location and detail of existing, proposed, and future block wall openings. Minimum size is 48“x16”. Wrought iron gate is required for storm flowrate, Q > 10cfs
  29. Location and detail of flood walls illustrating depth of flow, proposed grouting height, etc.
  30. Perimeter retaining wall locations. All existing and proposed walls (retaining screen and flood) must be shown with adjacent ground elevations. Flood walls with 8-inch concrete masonry unit (CMU)
  31. Building and/or lot numbers
  32. Alignment of all existing, proposed, or future Regional Facilities adjacent to the site
  33. Limits of existing floodplain based on current FIRM or best available information; limits of proposed floodplains based on best available information
  34. For areas in Zone A, AE, AH, and AO, base flood elevations (BFEs) must be shown for each lot; BFEs may be listed on each lot, or in a table. Finish floor elevations must be a minimum of 18 inches above the BFE
  35. Appropriate elevated “humps” 6 inches above the 100 year water surface elevation at site accesses where the intent is to protect the site from the storm flowrate, Q100 flows
  36. Street slopes for perimeter and interior streets. The minimum longitudinal slope is 0.4 percent.
  37. Location and detail of best management practice (BMP) for parking lots and low impact development (LID) if required
  38. Hydrologic Analysis
    1. Appropriate soil information and Soils Map for existing and future conditions with subbasins and property delineated
    2. Input and output information for existing conditions from computer models (HEC-1 or TR-55). The flow routing diagram must be provided with HEC-1 models.
    3. Input and output information for future conditions from computer conditions from computer models (HEC-1 or TR-55). The flow routing diagram must be provided with HEC-1 models.
    4. Use of correct precipitation values in and around the McCarran Airport rainfall area
    5. A discussion in the text of the hydrologic analysis justifying subbasin boundaries and cutoffs, supporting assumptions, and calculations
    6. A summary table of stormwater flows showing basin area, Q10 and Q100 for both individual basins and combined basin flows, where applicable
    7. Copies of supporting technical information referenced from a previously approved study and a statement accepting these results.
    8. On-site facilities must perpetuate flows through or around the site without significantly impacting adjacent property owners in accordance with current Nevada Drainage Law
    9. Calculation for impervious area for parking lots and LIDs (if required)
  39. Hydraulic Analysis
    1. Flow split calculations and supporting documentation or reference for the method of flow split calculations used
    2. Normal depth street flow calculations and cross section diagrams for all interior and perimeter streets. Provide “d x v” products for the Q10 and Q100 flows representing the worst case for interior and all perimeter streets. Q100 d x v = 8. Q10 d x v = 6 and 12 foot dry lane for rights-of-way = 80 feet. Calculations must be labeled by street name as indicated on the Grading Plan.
    3. A summary table of interior and exterior street capacity calculations showing the street name, Q100 flow, slope, depth of flow, velocity and depth times velocity (d x v) product and streets needing to meet 12 foot dry lane criteria
    4. Appropriate hydraulic calculations for block wall openings assuming a 50 percent vertical clogging factor. (Assume the lower half of the opening is plugged)
    5. Appropriate hydraulic calculations at drainage easement entrance and discharge locations to set finish floor elevations. Hydraulic calculations must include submerged weir, superelevation and tee intersection losses, where appropriate
    6. Provide necessary freeboard requirements to set the finished floor elevations of all proposed buildings, twice depth of flow (2 x D) or depth of flow plus 18 inches of freeboard (18“ + D), whichever is less. The minimum requirement is 6 inches above adjacent upstream top of curb (TC). Building adjacent to drainage easements must always be provided with 18 inches of freeboard above the Q100 weir height or flow depth, whichever is greater.
    7. A complete water surface profile analysis (HEC-2, HEC-RAS, etc.) for channel flows and FEMA Zone A flood zones.
  40. Field survey data
    1. Input and output information
    2. Plotted cross-sections based on survey with proper encroachments
    3. A map showing the location of the cross-sections
    4. Analysis of both sub and super-critical flow segments
    5. A summary table and a discussion of the results in the text of the report
  41. Provide a 50 percent clogging factor in the capacity calculation for drop inlets
  42. Hydraulic calculations for culverts and storm drains, D-Load calculations must be provided for storm drain pipes in public right-of-ways, including headwater pool inundation
  43. Mitigation of nuisance water, both during construction and in the fully developed condition, must be addressed
  44. Provide best management practice (BMP) type, size and supporting calculations for parking lots and low impact development (LIDs) (if required)

Drainage Submittal Checklist

Hydrology

Rational Method

  • It minimize runoff, Q use sub-basins having Time of Concentration, Tc near 6, 11, or 16 minutes. Very small sub-basins generate runoff of 9 cfs, which is significantly higher than the typical 3 cfs per acre in Las Vegas Valley.

Curve Number

  • Curve Number (CN) Value Evaluation
  • RFCD Drainage Design Manual Table 602 1 of 4 - Runoff Curve Numbers for Urban Areas
    • Need hydrologic soil group from RFCD Master Plan Update Figure H
    • If a coverage is not copied or deleted using Esri software options, such as ArcCatalog or a geoprocessing tool, it will not be copied or deleted correctly. Never copy a coverage using Windows Explorer; otherwise, your data will be corrupted. (ArcGIS 10.3 Contents of a coverage workspace)
    • RFCD subbasins shapefile gives a Weighted CN (WCN) for each subbasin.

HEC-1

Reservoir Storage Data

  • “A reservoir storage volume versus elevation relationship is required for level-pool reservior routing. The relationship may be specified in two ways: 1) direct input of precomputed storage versus elevation data, or 2) computed from surface area versus elevation data.” (HEC-1 Flood Hydrograph Package User's Manual, p. 44)

Calculate Reservoir Storage from Inflow and Outflow

  • “HEC-1 can compute changes in reservoir storage using the current hydrograph as inflow and a user-defined hydrograph as outflow. The HS record is used to tell the program to computer storage from the inflow and outflow. The outflow hydrograph is read from QO records, and is used in downstream calculations. Initial storage at the beginning of the simulation is set on the HS record in the first field.” (HEC-1 Flood Hydrograph Package User's Manual, p. 50)
  • HEC-1 Manual example problem 14, section 12
  • Developed Condition as the inflow hydrograph
    • “The HEC-1 data input file must be structured so that the proposed detention basin site is a hydrograph routing or hydrograph combining point.” (RFCD Drainage Design Manual 1203.1.1)
  • Existing Condition as the outflow hydrograph uses the QO records
    • QO Record - p. A-59 on hec1_Manual.pdf
    • observed flow in cfs at beginning of first period
  • HS record tells the program to computer storage

Hydraulics

  • Full width hydraulic street analysis - assumptions
    • Vertical walls at edge of right of way
    • Flow, Q is equally divided on each half of the street
      • otherwise would have to do some side weir calculation/analysis which might be discussed by Chow
  • FlowCalc by John Hamilton
    • Mannings n = 0.017 for Asphaltic Concrete (AC) or pavement (sometimes 0.016 for roadways)
    • Mannings n = 0.013 for concrete (Portland cement)
    • Cannot size drop inlets, needs FlowMaster or FHWA Toolkit instead
  • Drop Inlet sizing

WSPGW by CivilDesign

Detention Pond

  • Flap Gates or Duckbill/Pinch Check Valves
    • “Flap gates or duckbill valves are installed at or near sewer outlest to prevent back-flooding of the sewer system by high tides or high stages in the receiving stream. These are common only in combined or storm sewers. Duckbill valves are made of elastomers which are NOT susceptible to corrosion. They are commercially available in sizes up to 96-inch (2,438-mm) diameter. The valves have been found to be self-cleansing.” (Gravity Sanitary Sewer Design and Construction, 2nd, p. 210, ASCE Manuals and Reports on Engineering Practice No. 60, WEF Manual of Practice No. FD-5)
    • Duckbill Valve
  • City of Provo
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