HomeMy WebLinkAboutFile Documents.39 Boomerang Rd.0039.2018 (2).ACBK Major Project
CITY OF ASPEN ENGINEERING DEPARTMENT
Ti iE Ciro'OF ASPEN GRADING AND DRAINAGE REQUIREMENTS
FOR MAJOR DESIGN
If the project will increase impervious area by more than 1000 SF or 50% of the existing
site imperviousness (this includes changing a gravel driveway to hard surface, adding
hard surface patios, increasing the footprint of the house, etc.), disturb>1000 SF of land
(this includes grading, even if a structure or hard surface is not added, as well as "scrape
and replace"), or add or repair snowmelt then an analysis of stormwater runoff via a
Grading and Drainage Plan and Report are required, unless determined by the
Development Engineer to be unnecessary. The Plan and Report must be signed and
stamped by a Colorado Professional Engineer. One copy of the Report and one copy of
the Plans set is required for Sufficiency Review. Three copies of each will be required
for Building Permit Application.
DRAINAGE REPORT SHALL INCLUDE: �-/ i S 0
G,eneral /��3 f
Signature, date, and stamp of a Colorado Professional Engineer. I S-l6
De Description of the existing site, including common location, topography, land use,
so'ground cover, - e, drainage pattern, and Isssiyingsysteffh—
ir
Description of the proposed project, including changes to land use, topography,
ground cover, soil type, drainage pattern and receiving system.
Discussion of any previous drainage studies (i.e.,project master plans) for the site
that influence or are influenced by the drainage design and the mitigation plan for any
/negative impacts.
Discussion of the effects of adjacent drainage issues.
ti Reference to major drainage way planning studies such as flood hazard delineation
reports, master plans, and flood insurance rate maps.
64/ Discussion of the drainage impact of site constraints such as streets, utilities, existing
structures, and development or site plan.
'o Identification of all irrigation facilities and waterways within the watershed that will
influence or be influenced by the site drainage.
V Discussion of easements and tracts for drainage purposes, including the conditions
and limitations for use.
I Report must include printed copies of the input and output files for all computer
/models used for the analysis and design.
>I Reference plan drawings as needed.
`Dpinage Basins and Sub-basins (background info provided in 1996 report)
Describe existing and proposed sub-basins, including ground cover, acreage, soil
type, and location and method of discharge.
'F1 Delineate and reference sub-basins on a map with contours. Each drainage basin
should be labeled with its area(in acres),runoff coefficient(C), and Q (cfs).
g/ Discuss offsite drainage patterns and impact on site under existing basin conditions
and fully-developed basin conditions.
b Discuss pre-developed/historic and post-developed drainage flow rates at specified
point locations (should match labeled locations on plan). RE r F
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Low Impact Site Design
ti Describe what efforts have been made to reduce runoff and increase infiltration(e.g.
reduce impervious area, disconnect impervious area, route runoff via landscape rather
than hard infrastructure).
VHydrologic Criteria (confirmed for WQCV of pavement area, 1996 report for AHV in general)
Identify design storm recurrence intervals.
NO Identify design rainfall.
V/ Identify runoff calculation method.
'tof Identify detention discharge and storage calculation method.
Discussion and justification of other criteria or calculation methods used that are not
presented in or referenced by the criteria.
tr Identify the area, storm frequency, rainfall intensity, time of concentration, runoff
coefficients, and adjustments for each sub-basin.
'b Calculate existing runoff or historic runoff as appropriate. Refer to Section 5.2 of the
URMP.
•N Calculate the post development runoff flows for each sub-basin and compare these
flows to pre-development flows. Post development flows must not exceed pre-
development flows. Determine post development flow prior to inclusion of detention.
Flow should be calculated for each location that runoff leaves the site. Each drainage
basin should be labeled with its area(in acres), runoff coefficient(C), and Q (cfs).
Provide calculations of the WQCV, minor event(5-yr for drywell, 5- or 10-year for
storm system and detention) and major storm runoff(100yr) at specific design points.
l� Hydrographs at critical design points.
Hydraulic Criteria (confirmed for WQCV of pavement area and new Outlet, 1996 report for AHV in general)
'' Identify the hydraulic design point for closed systems tied to the City's existing
collection system.
J Identify flow capacity of drainage facilities.
Calculate culvert sizes with capacities and area of contribution.
Calculate storm sewer capacity including capacity of next two downstream drainage
structures (max velocity 20 ft/sec, HGL 12 inches below ground, EGL below ground,
minimum velocity of 5 ft/sec at half full conduit flow).
Calculate gutter capacity(max velocity 10 ft/sec, allowable spread=4 feet minor
storm, 12-inch depth at flow line for major storm, n=.016 for street, n=.025 for grass)
Calculate storm inlet capacity (clogging factor= 50%).
X Provide open channel design and calculations.
'5( Check and/or channel drop design.
Calculate the downstream/outfall system capacity to the major drainage way system.
Proposed Facilities (provided for WQCV of pavement area and new Outlet)
bi Describe proposed better site design practices (BMPs)used to treat the water quality
1 f capture volume, detention methods and outlet design with protection techniques.
'h Provide sizing calculations and approximate locations, with drainage basins, of BMPs
used to treat the water quality capture volume.
65 Provide volumes and release rates for detention storage facilities and information on
outlet works. R / l Ui)
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Discussion of easements and tracts for drainage purposes, including the conditions
and limitations for use.
Discussion of the off-site drainage facilities needed for the conveyance of minor and
major flows to the major drainage way.
Provide a separate section of the report that includes a narrative of the Operation and
Maintenance requirements of the proposed on site drainage improvements. Include a
description of access for maintenance operations, maintenance schedule, and contact
information for party responsible for maintenance.
GRADING AND DRAINAGE PLANS SHALL INCLUDE; refer to report for
"unchecked"
boxes
-o Signature, date, and stamp of Colorado Professional Engineer on each plan sheet.
-B Vicinity map with north arrow and scale.
e. Drawings must be 24" x 36" in size.
�- Scale of 1"=10' to 1"=40' or plan must be provided in sufficient detail and clarity to
identify drainage flows entering and leaving the development and general drainage
patterns.
o Benchmark and tie to the City of Aspen Survey. survey not updated
o Name of the subdivision or project,property map and parcel number.
Date of preparation, scale, and symbol designating true north.
>r Legend to define map symbols.
- - Property lines and easements with purposes noted.
.e Existing and proposed contours at 1-foot maximum intervals. In terrain where the
slope exceeds 15%, the maximum interval is 10 feet. The contours shall extend a
minimum of 100 feet beyond the property lines. Additional topography can be
obtained from the City of Aspen GIS Department.
o Overall drainage area boundary and drainage sub-area boundaries for all basins on
and off site.
❑ Location, elevation, and FIRM rate code for all existing floodplains within 100' of
property.
All major drainage ways for which the 100-year floodplain and floodway have been
defined shall have the 100-year floodplain and floodway delineated on the plans. This
also applies to detention basins.
❑ Indicate the top of slope of tlI-Roaring Fork River and its tributaries (Hunter Creek,
Castle Creek, and Maroon Creek) and delineate the 15' no-touch setback.
❑ Existing building footprints, streets, utility locations and elevations, ROW width,
flow line width, curb type, sidewalk, approximate slopes, drainage facilities and
structures, irrigation ditches, roadside ditches, drainage ways, gutter flow directions,
and culverts. All pertinent information such as material, size, shape, slope, and
location shall also be included.
❑ Proposed building footprints, streets, utility locations and elevations, ROW width,
flow line width, curb type, sidewalk, approximate slopes, drainage facilities and
structures, irrigation ditches, roadside ditches, drainage ways, gutter flow directions,
and culverts. All pertinent information such as material, size, shape, slope, and
location shall also be included.
❑ Proposed type of street flow (i.e., vertical or combination curb and gutter), roadside
ditch, gutter, slope and flow directions, and cross pans.
o Proposed storm sewers and open drainage ways, including inlets, manholes, culverts
and other appurtenances, (i.e. riprap protection, allowable manhole spacing=40 E iVE lit/
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b_ Proposed landscaping(berms, planters, shrub beds,frees, etc.). Overlay the
actual landscape plan onto the proposed grading and drainage plan.
❑ Profile views for all subsurface drainage facilities showing their size, slope, lengths,
design storm hydraulic grade lines (major and minor), energy grade lines, cover,
details of structures and/or City Standard details, and relationship with existing
utilities. (18 vertical clearance for storm from water lines, 5 foot horizontal from any
utility, 7 feet below ground surface, 2 % slope minimum, 18 inch min for main, 15
inch min for lateral).
❑ Cross-sectional views of all open channels, including irrigation ditches, trickle
channels, spillway structures, etc., as necessary. These views shall include applicable
easement/property line/ROW boundaries and water surface elevations such as the
100-year storm depth, 2-year storm depth, major storm (100-year) freeboard, and
irrigation operating level.
❑ Finished floor and grade at foundation elevations of all buildings. In residential
developments also provide lot corner elevations and any grade break elevations
critical to the grading concept. Show positive drainage away from structures as
required by Building Code (IRC—R401.3 and IBC — 1805.3.4).
❑ Spot elevations critical to describe drainage features and their functions (e.g. inlets,
cross pans, spillways, inlets/outlets of manholes, culverts, and storm sewers).
14 Proposed outfall point for runoff from the developed area and facilities to convey
flows to the final outfall point without damage to downstream properties.
❑ Routing and accumulation of flows at various critical points for the initial and major
storm runoffs listed on the drawing.
❑ Routing of offsite drainage flow through the development.
❑ Flow path leaving the development through the downstream properties ending at a
major drainage way.
❑ Summary Runoff Table.
Is, Natural hazards: The designation of all areas that constitute natural hazard areas
including but not limited to snow slide, avalanche, mudslide, and rockslide. Show
areas with slopes from 30% to 40% and areas with slopes greater than 40%. Areas
with slopes from 30%to 40%and areas with slopes greater than 40%will require a
slope stability study performed by the Colorado Geological Survey (800-945-0451).
—ea- Civil details of dry wells, outlet structures, foundation drain sumps, custom design,
etc.
--p- Erosion prevention and sediment control measures for all phases of construction,
including areas of revegetation.
^o Profile views for all subsurface drainage facilities showing their size, slope, lengths,
design storm hydraulic grade lines (major and minor), cover, details of structures
and/or City Standard details, and relationship with existing utilities. (18 vertical
clearance for storm from water lines, 5 foot horizontal from any utility, 7 feet below
ground surface, 2 % slope minimum, 18 inch min for main, 15 inch min for lateral).
❑ Cross-sectional views of all open channels, including irrigation ditches, trickle
channels, spillway structures, etc., as necessary. These views shall include applicable
easement/property line/ROW boundaries and water surface elevations such as the 5 or
10-year storm depth, major storm 100-year, and irrigation operating level.
REcnvEu
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BUILDING DEPARTMENT