STORM DRAINAGE DESIGN
DRAINAGE PLANNING SUBMITTAL
REQUIREMENTS
1. REVIEW PROCESS
All
subdivisions, resubdivisions, Planned Unit Developments or any other
development or redevelopment done within the jurisdiction of the
1.1 Subdivision Process
The general requirements for the subdivision of land in the TOWN and conditions requiring subdivision, are set forth in Title 9 of Elizabeth Municipal Code.
2. DRAINAGE REPORT
Depending
on the size and complexity of the drainage system, both a preliminary and final
drainage report may be required. Three
(3) copies of the drainage report, prepared and signed by a Professional
Engineer registered in the State of
Reports shall be cleanly and clearly reproduced and legible throughout. Blurred or unreadable portions of the report will be deemed unacceptable and will require resubmittal. Incomplete or absent information may require resubmittal of the report.
The
applicant shall note that approval of construction plans, specifications, and
associated engineering reports by the TOWN shall indicate only that the plans,
specifications, and reports are in conformance with submittal requirements and
current design criteria, that standard engineering principles and practices
appear to have been followed, and that the plans and reports appear to be in
conformance with existing approved plans and reports: approval shall not
indicate that all assumptions, calculations, and conclusions contained therein
have been thoroughly verified by the TOWN.
The professional engineer submitting the plans, specifications, and
reports shall, at all times, be solely responsible for their accuracy and
validity. If during the construction
process, or at any time within two years following the acceptance by the TOWN
of the completed improvements, any deficiencies or errors are discovered in the
plans, specifications, reports or in the actual improvements as built, the TOWN
shall have the right to require any and all corrections which may be deemed
necessary by the TOWN. The costs
associated with any such corrections shall be the sole responsibility of the
developer. Decisions by TOWN Staff
members requiring the developer or engineer to make corrections and bear the
costs thereof may, upon written request made within fifteen (15) days of the
TOWN’s written notification to the developer or consultant, be appealed to the
A pre-submittal conference is suggested in cases involving large development or redevelopment or where special conditions or problems have become apparent during the development review process.
2.1 Preliminary Drainage Report
At the time of land zoning, rezoning, or proposal for development or redevelopment, a preliminary drainage report may be required in advance of the final drainage report.
2.2 Preliminary Drainage Report Contents
The purpose of the Preliminary Drainage Report is to identify and define conceptual solutions to drainage problems which may occur on site and off site as a result of development. In addition, problems that exist on site prior to development shall be addressed during the preliminary phase.
All
reports shall be typed and bound on 8 1/2” x 11” paper with pages numbered
consecutively. Any drawings, figures,
plates and/or tables shall be bound with the report or included in
folders/pockets attached inside the back cover of the report. The report shall be prepared or supervised by
an engineer licensed in
It should be emphasized that many of the requirements described in the following report format may not be possible to meet. For example, there may be no master drainage plan or defined flood plain for a particular major drainage way. Where this is the case, these facts shall be discussed and the absence of certain information noted. The report format is intended to be a guideline, and as such, shall not necessarily prohibit the completion of a drainage study due to lack of specific information. However, the report shall be as complete as the factual situation will allow.
Each preliminary drainage report shall provide the following:
I. GENERAL LOCATION
A. Location
1.
3. Major drainageways and facilities.
4. Names of surrounding developments.
B. Description of Property
1. Area in acres.
2. Existing ground cover (type of trees, shrubs and vegetation).
3. Existing major irrigation facilities such as ditches and canals.
4. Proposed land use and proposed ground cover.
5. Identification of all wetland areas with total wetland acreages given.
II.
DRAINAGE BASINS
A.
1. Reference to major drainageway planning studies (if any) such as flood hazard delineation reports, major drainageway planning reports, and flood insurance rate maps.
2. Describe major basin drainage characteristics, and existing and planned land uses within the basin, as defined by the Director of Community Development.
3. Identify all irrigation facilities within the basin that will influence or be influenced by the proposed site drainage.
4. Identify (include ownership) all lakes and ponds which either influence or may be influenced by the local drainage.
B. Sub-Basin Description
1. Describe historic drainage patterns of the property.
2. Describe offsite drainage flow patterns and impact on development under existing and fully developed basin conditions. This may require delineation and mapping of off site drainage basins.
A. General Concept
1. Discuss proposed drainage concept and how it fits existing drainage patterns.
2. Discuss how offsite runoff will be considered and how expected impacts will be addressed.
3. Discuss stormwater quantity and quality management concept and how it will be employed.
4. Describe the content of tables, charts, figures, plates, drawings and design calculations presented in the report.
5. Discuss maintenance and maintenance access as it relates to drainage and drainage structures.
6. Discuss wetlands issues (if any), mitigation, replacement, etc.
B. Specific Details
1. Discuss drainage problems, including stormwater quality, and solutions at specific design points.
2. Discuss detention storage and outlet design.
3. Discuss impacts of concentrating flow on downstream properties.
C. Variances from CRITERIA and/or MANUAL
1. Identify provisions by section number for which a variance is requested.
2. Provide specific and detailed justification for each variance requested.
IV. SUMMARY/CONCLUSIONS
A. Provide overall summary including conclusions and professional opinions on the
adequacy of the proposed facilities.
B. Include an engineer’s certification that reads as follows:
“This
report for the preliminary drainage design of (Name of Development) was prepared by me (or under my direct
supervision) in accordance with the provisions of
SIGNATURE: _________________________
Registered Professional Engineer
State of
No. ______________
(Affix Seal)
V. REFERENCES
Reference all criteria, master plans, and technical information used in support of concept.
2.3 Preliminary Drainage Report Drawing
Contents
(a) General Location Map: All drawings shall be 24” x 36” in size. A map shall be provided in sufficient detail to identify drainage flows entering and leaving the development and general drainage patterns. The general location map should be at a scale of 1” = 500' to 1" = 4000' and show the path of all drainage from the upper end of any offsite basins to the defined major drainageways. The map shall identify all major construction (i.e., development, irrigation ditches, existing detention facilities, stormwater quality facilities, culverts, storm sewers, etc.) along the entire path of drainage. Basins and divides shall be identified and topographic contours shall be included.
(b) Flood Plain Information: Flood plain limits (if any) shall be shown on all report drawings. The source and date of the flood plain limits shown (e.g., flood hazard area delineation, flood insurance rate map, etc.) shall be noted on the drawings.
(c) Drainage Plan: Map(s) of the proposed development at a scale of l” = 20' to 1” = 200' (or of sufficient scale to portray the drainage plan in adequate detail) on a 24” x 36” drawing shall be included. The plan shall show at least the following:
1. Existing topographic contours (dashed lines) at 2-feet maximum intervals. In areas of little relief, 1-foot contours shall be shown. In terrain where the slope exceeds 15%, the maximum interval is 5 feet. The contours shall extend a minimum of 100 feet beyond the property lines.
2. Proposed topographic contours (solid lines) at 2-feet maximum intervals. In areas of little relief, 1-foot contours shall be shown. Proposed contours shall match existing contours around the boundary of the proposed project.
3. Existing vegetation.
4. All existing wetland areas.
5. Property lines and easements with purposes noted.
6. Building outlines and first floor elevations of all existing and proposed structures.
7. Streets, if applicable, indicating
8. Existing drainage facilities and structures within map limits, including irrigation ditches, roadside ditches, drainageways, gutters, inlets, detention basins and culverts.
9. Major drainage basin boundaries and sub-boundaries.
10. Conceptual major drainage facilities including proposed stormwater quality Best Management Practices (see MANUAL, Volume 3), detention basins, storm sewers, swales, riprap, and outlet structures in the detail consistent with the proposed development plan.
11. Flooding limits based on available information.
12. Any offsite feature that influences the proposed development drainage.
13. Proposed drainage patterns, including flow direction arrows.
14. Legend to define map symbols.
15. Project name, address, engineering firm and seal, and original and revision dates in title block in lower right corner.
16. North arrow, scale and available bench mark information and location for each bench mark.
3. FINAL DRAINAGE REPORT
The final drainage report serves to define and expand the concepts shown in the preliminary report and presents the final design details for the drainage facilities discussed in the Preliminary Drainage Report. This report must be written in such a manner, and contain enough detail, that it is self-explanatory (i.e., possession of the Preliminary Drainage Report is not necessary to understand the Final Drainage Report). The final report may be submitted at any point during the permitting and platting process, but must be reviewed and approved prior to issuance of any permit.
Three (3) copies of the report shall be submitted to the Director of Community Development. Reports shall be typed and bound on 8-1/2" x 11" paper with pages numbered consecutively. Drawings, figures, tables, etc., shall be bound with the report or contained in attached pockets. The report shall include a cover letter presenting the design for review prepared or supervised by a Professional Engineer licensed in the State of Colorado.
It should be emphasized that many of the requirements described in the following report format may not be possible to meet. For example, there may be no master drainage plan or defined flood plain for a particular major drainage way. Where this is the case, these facts shall be discussed and the absence of certain information noted. The report format is intended to be a guideline, and as such, shall not necessarily prohibit the completion of a drainage study due to lack of specific information. However, the report shall be as complete as the factual situation will allow.
The developer or his consultant is responsible for obtaining any and all permits, licenses, and any other documentation/correspondence that are necessary to address any wetlands issues impacting the given project.
3.1
Final Drainage Report Contents
The report shall be in accordance with the following outline and contain the following information:
I.
GENERAL LOCATION
A. Location
1.
2. State highway and local streets within and adjacent to the site, or the area to be served by the drainage improvements.
3. Major drainageways, facilities, and easements within and adjacent to the site.
4. Names of surrounding developments, land uses, and identification of present zoning.
B. Description of Property
1. Area in acres.
2. Existing ground cover (type of trees, shrubs, vegetation, general soil conditions, topography, and slope).
3. All drainageways.
4. Existing irrigation facilities such as ditches and canals.
5. Proposed land use and proposed ground cover.
6. General project description.
7. Identification of all wetland areas with total wetland acreages given.
II. DRAINAGE BASINS
A. Major Basin Description
1. Reference major drainageway planning studies (if any) such as flood hazard delineation reports, major drainageway planning reports, and flood insurance rate maps.
2. Describe major basin drainage characteristics, and existing and planned land uses within the basin, as defined by the Director of Community Development.
3. Identify all irrigation facilities within the basin that will influence or be influenced by the proposed site drainage.
4. Identify (include ownership) all lakes and ponds which either influence or may be influenced by the local drainage.
B. Sub-Basin Description
1. Describe historic drainage patterns of the property.
2. Describe offsite drainage flow patterns and impact on development under existing and fully developed basin conditions, as defined by the Director of Community Development. This may require delineation and mapping of off site drainage basins.
A. Regulations
1. Describe the use of optional provisions and any deviation from these CRITERIA and justification for such actions.
B. Development Criteria Reference and Constraints
1. Describe previous drainage studies (e.g., project master plans, preliminary drainage reports, etc.) for the site that influence or are influenced by the drainage design and how implementation of the plan will affect drainage and stormwater quality for the site.
2. Describe the effects of adjacent drainage studies.
3. Describe the drainage impact of site constraints such as streets, utilities, existing structures, and development on site plan.
C. Hydrologic Criteria
1. Identify design storm rainfall and its return period(s).
2. Identify runoff calculation method(s).
3. Identify detention discharge and storage calculation method(s).
4. Describe and justify other criteria or calculation methods used that are not presented in or referenced by the CRITERIA or MANUAL.
D. Hydraulic Criteria
1. Identify street capacity references.
2. Identify other capacity references, if applicable.
3. Identify detention outlet design method.
4. Identify check/drop criteria used, if applicable.
5. Describe other drainage facility design criteria used that are not presented in these CRITERIA or the MANUAL.
E. Stormwater Quality Criteria
1. Identify Best Management Practices to be used for stormwater quality control.
2. Identify, as appropriate, water-quality capture volume and drain time for extended-detention basins, retention ponds and constructed wetland basins.
3. Identify, as appropriate, runoff volume and flow rates for design of water-quality swales, wetland channels and porous pavement.
4. Describe other stormwater quality design criteria used that are not presented in these CRITERIA or the MANUAL.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. Describe proposed drainage concept and how it fits existing drainage patterns.
2. Describe how offsite runoff will be considered and how expected impacts will be addressed.
3. Describe the content of tables, charts, figures, plates, or drawings presented in the report.
4. Describe the contents of referenced reports, studies, etc.
5. Describe proposed stormwater quality management strategy.
B. Specific Details
1. Describe drainage problems encountered and solutions proposed at specific design points.
2. Describe detention storage and outlet design requirements.
3. Describe maintenance and maintenance access as it relates to drainage and drainage structures.
4. Describe wetlands issues (if any), mitigation, replacement, etc.
5. Describe easements and tracts for drainage purposes, including the conditions and limitations for use.
6. Describe impacts of concentrating flow on downstream properties.
7. Describe stormwater quality Best Management Practices to be used.
C. Variances from CRITERIA and/or MANUAL
1. Identify provisions by section number for which a variance is requested.
2. Provide specific and detailed justification for each variance requested.
V. SUMMARY/CONCLUSIONS
A. Discussion of Compliance with Standards by Proposed Drainage Plan.
1. CRITERIA
2. Major Drainageway Planning Studies
3. MANUAL
B. Discussion of Final Drainage Concept
1. Effectiveness of drainage design to control damage from storm runoff.
2. Effectiveness of design to remove pollutants from storm runoff.
3. Influence of proposed development on the Major Drainageway Planning Studies recommendation(s), if any.
C. Include an engineer’s certification that reads as follows:
“This
report for the final drainage design of (Name of Development) was
prepared by me (or under my direct supervision) in accordance with the
provisions of
SIGNATURE: __________________________
Registered Professional Engineer
State of Colorado
No. ______________
(Affix Seal)
D. Include a developer’s certification that reads as follows:
“(Name
of Developer) hereby affirms that the drainage facilities for (Name of
Development) shall be constructed according to the design presented in this
report and plan. I understand that the
SIGNATURE: (Signature of Developer)
NAME: (Typed or Printed Name of Developer)
TITLE: (Official Title of Developer)
VI. REFERENCES
Reference all criteria and technical information used.
A. Hydrologic Computations*
1. Land use assumptions regarding adjacent properties.
2. Initial and major storm runoff at specific design points.
3. Historic and fully-developed runoff computations at specific design points.
4. Hydrographs at critical design points, if necessary for clarity.
5. Times of concentration and runoff coefficients for each basin.
6. Stormwater quality Best Management Practice sizing calculations, including runoff adjustments for minimizing directly-connected impervious areas.
B. Hydraulic Computations*
1. Culvert design calculations and capacities (existing and proposed).
2. Storm sewer design calculations and capacities, including energy grade line (EGL) and hydraulic grade line (HGL) elevations.
3. Gutter and street cross-section capacities as compared to allowable capacities based on allowable pavement encroachment.
4. Storm inlet capacities considering appropriate clogging factors at connection to storm sewer.
5. Open channel design.
6. Check and/or channel drop structure design.
7. Riprap design calculations.
8. Detention area/volume capacity and outlet capacity calculations for flood detention and water quality basins; depths of detention basins.
9. Wetland area and area/depth distribution for constructed wetland basins.
10. Infiltration rates and volumes for porous pavement or release rates where underdrains or infiltration are not possible.
11. Flow rates, velocities, longitudinal slopes and cross-sections for wetland channels and water quality swales.
12. Downstream/outfall system capacity to the Major Drainageway System.
* Include any input and output listings for any computer models used.
3.2 Final Report Drawing Contents
(a) General Location Map: All drawings shall be 24” x 36” in size. A map shall be provided in sufficient detail to identify drainage flows entering and leaving the development and general drainage patterns. The location map should be at a scale of l” = 500' to 1” = 4000' and show the path of all drainage from the upper end of any offsite basins to the defined major drainageways. The map shall identify all major construction (i.e., development, irrigation ditches, existing detention facilities, stormwater quality facilities, culverts, storm sewers, etc.) along the entire path of drainage. Basins, along with basin identification numbers, and divides shall be identified and topographic contours shall be included.
(b) Floodplain Information: Flood plain limits (if any) shall be shown on all report drawings. The source and date of the flood plain limits shown (e.g., flood hazard area delineation, flood insurance rate map, etc.) shall be noted on the drawings.
(c) Drainage Plan: Map(s) of the proposed development at a scale of l” = 20' to l” = 200' (or of sufficient scale to portray the drainage plan in adequate detail) on a 24” x 36” drawing shall be included. The plan shall show the following:
1. Existing (dashed lines) and proposed (solid lines) topographic contours at 2-feet maximum intervals. In areas of little relief, 1-foot contours shall be shown. In terrain where the slope exceeds 15%, the maximum interval is 5 feet. The contours shall extend a minimum of 100 feet beyond the property lines. Proposed contours shall match existing contours around the boundary of the proposed project.
2. Existing and proposed vegetation.
3. All existing wetland areas.
4. Property lines, existing easements, and easements proposed for dedication, with purposes noted.
5. Building outlines, square footage and first floor elevations of all existing and proposed structures.
6. Streets, indicating
7. Proposed type of street flow (i.e., vertical or combination curb and gutter), roadside ditch or swale, gutter, slope, flow direction, and cross pans.
8. Existing drainage facilities and structures within map limits, including irrigation ditches, roadside ditches, cross pans, drainageways, storm sewers, swales, riprap, gutter flow directions, inlets, detention basins and culverts. Pertinent information, such as material, size, shape, slope, flow line elevations and location, shall also be included.
9. Overall tributary drainage basin area boundary and drainage sub-basin boundaries. Label drainage sub-basins as shown in Table 1.
10. Proposed storm sewers and open drainageways, inlets, manholes, culverts, and other appurtenances, including riprap or other erosion protection. Show flow line elevations throughout the site and invert elevation(s) at system outfall(s).
11. Proposed structural water-quality Best Management Practices, their location, sizing, and design information.
12. Proposed outfall point for runoff from the developed area and, if required, facilities to convey flows to the final outfall point without damage to downstream properties. Show flow path leaving the development through the downstream properties ending at a major drainageway or receiving water.
13. Routing and accumulation of flows at various critical points for the initial storm runoff event, listed on the drawing using the format shown in Table 1.
14. Routing and accumulation of flows at various critical points for the major storm runoff events, listed on the drawing using the format shown in Table 1.
15. Volumes and release rates for detention storage facilities and water-quality capture volumes.
16. Detailed information on detention storage and water-quality facilities and their corresponding outlet structures.
17. Location and water surface profiles or elevations of all previously defined floodplains affecting the property. If floodplains have not been previously published, they shall be defined and shown on the drainage plan, if applicable.
18. Location, and measured or estimated elevations, of all existing and proposed utilities affected by or affecting the drainage design.
19. Routing of upstream offsite drainage flow through the development.
20. Legend to define map symbols.
21. Project name, address, engineering firm and seal, and original and revision dates in title block in lower right hand corner.
22. North arrow, scale and available bench mark information and location for each bench mark.
4. CONSTRUCTION PLANS
For
on-site drainage improvements, the final construction plans (24" x
36") shall be submitted after approval of the Final Drainage Report. Seven (7) sets of plans shall be submitted
for approval. Upon approval, four sets,
stamped and signed, will be returned to the design engineer for use by the
contractor, owner and design engineer.
However, before any construction work begins, appropriate bonds,
letters-of-credit, or other surety should be issued to the
1. Plan and profile of proposed storm sewer installations, inlets, outlets and manholes with pertinent elevations, dimensions, type and horizontal control shown.
2. Culverts, end sections, and inlet/outlet protection with dimensions, type, elevations, and horizontal control indicated.
3. Other drainage-related structures and facilities (including underdrains and sump pump lines)..
4. Property and right-of-way lines, existing and proposed structures, fences and other land features.
5. Plan and profile of existing and proposed channels, ditches, swales, and on-site water quality Best Management Practices with construction details, cross-sections and erosion controls shown.
6. Detention and water quality (if separate) facility grading, trickle channels (if any), outlet and inlet locations, cross-sections or contours sufficient to verify volumes, etc..
7. Details of inlet and outlet control devices and of all structural components being constructed.
8. Maintenance access considerations and details.
9. General overlot grading and the erosion and sediment control plan prepared in accordance with applicable provisions of these CRITERIA and the MANUAL.
10. Landscaping and revegetation plans and details.
11. Proposed finish floor elevations of structures.
12. Relation of site to current and, if appropriate, modified floodplain boundaries.
13. Any and all wetland mitigation details.
14. A statement agreeing to maintain and operate
all privately-owned facilities (if any) in a working manner and/or in
accordance with the requirements of the Colorado Water Quality Control Division
specified in the stormwater discharge permit issued to the
15. Signature and seal of the Colorado professional engineer preparing these plans.
The information required for the plans shall be in accordance with sound engineering principles, these CRITERIA, and the TOWN requirements for subdivision designs. Construction documents shall include geometric, dimensional, structural, foundation, bedding, hydraulic, land