Skip to code content (skip section selection)
(A) Phase I drainage report requirements. This report will review at a conceptual level the feasibility and design characteristics of the proposed subdivision. The Phase I drainage report shall be submitted with the preliminary plan and shall be in accordance with the following outline and contain the applicable information listed.
(1) Report contents.
(a) General location and description.
a. Township, range, section, one-quarter section;
b. City, county, state highway and local streets showing R.O.W. widths within and adjacent to the subdivision, or the area to be served by the drainage improvements, within one-fourth mile;
c. Names of surrounding developments, land uses and identification of present zoning; and
d. Area in acres.
2. Description of property.
a. Ground cover (type of trees, shrubs, vegetation, general soil conditions, topography and slope);
b. All drainageways;
c. Existing slopes and rock outcroppings; and
d. General project description.
3. Existing irrigation facilities. Existing irrigation facilities such as ditches and canals within or near project (note if still in use).
4. Existing proposed land use. Existing or proposed land use with approximate area breakdown and intent for complete over lot grading or other approach.
(b) Drainage basins and sub-basins.
1. Major basin description.
a. Reference to all drainageway planning studies such as flood hazard delineation report, drainageway planning reports and flood insurance rate maps;
b. Existing major basin drainage characteristics; and
c. SCS Soils Classification Map.
2. Sub-basin description.
a. Historic drainage patterns of the property in question; and
b. Off-site drainage flow patterns from tributary areas and impact on development under existing and fully developed basin conditions as defined by the Engineering Department.
(c) Drainage facility design.
1. General concept overview.
a. Concept and typical drainage patterns;
b. Compliance with off-site runoff considerations;
c. Anticipated and proposed drainage patterns; and
d. Storm water runoff quality aspects of the drainage design.
2. Specific details overview.
a. Drainage problems encountered and solutions at specific design points;
b. Detention storage and outlet design (design calculations not required in this phase);
c. Maintenance and access aspects of the design;
d. Easements and tracts for drainage purposes; and
e. Any variances from these regulations and justification for variance request.
(d) References. Reference all criteria, master plans and technical information used in support of concept.
(2) Drawing contents.
(a) General location map. A map shall be provided in sufficient detail to identify drainage patterns entering and leaving the development and general drainage patterns. The map should be at a scale of one inch equals 2,000 feet and show the pattern of all drainage for all basins which affect, or are affected by, the property in question. (U.S.G.S. Quad Sheets are ideal for this purpose.) Compliance with copyright law is the responsibility of the Consultant Engineer, from the upper end of said basins to defined major drainageways. The map shall identify any major facilities form the property (i.e., development, irrigation ditches, existing detention facilities, culverts and storm sewers) along the flow path to the nearest drainageway. Basins and divides are to be identified and topographic contours are to be included.
(b) Floodplain information. A copy of the applicable FIRM panel. One hundred-year floodplain boundaries shall be shown on the preliminary plat and final plat.
(c) Drainage plan. Map(s) of the proposed development at a scale of one inch equals 20 feet to one inch equals 200 feet on a 24-inch by 36-inch drawing shall be included. The plan shall show the following:
1. Existing (dashed lines) and, if available, proposed (solid-line) topographic contours at two-feet maximum intervals. In terrain where the slope exceeds 15%, the maximum interval is ten feet. The contours shall extend a minimum of 100-feet beyond the property lines, unless otherwise authorized by the Director;
2. Property lines and easements with purposes noted;
3. All existing drainage facilities;
4. Approximate flooding limits based on available information;
5. Conceptual major drainage facilities including detention basins, storm sewers, sewers, riprap and outlet structures in the detail consistent with the proposed development plan;
6. Major drainage boundaries and sub-boundaries;
7. Any off-site feature influencing development;
8. Proposed flow directions and, if available, proposed contours;
9. Streets with R.O.W. width if available;
10. Legend to define map symbols;
11. Title block in lower right corner; and
12. North arrow, graphic and written scale and written contour interval.
(B) Phase II drainage report.
(1) The purpose of this report is to finalize all design details which were either not covered in the Phase I drainage report, or which require adjustments resulting from the completion of the construction plans. All aspects of this design for all drainage facilities must be shown and supported in detail. Phase II reports are typically required at final plan stage.
(2) In addition to the Phase I drainage report requirements, the following will be required in the Phase II drainage report.
(a) Report contents.
1. Drainage design criteria. The optional provisions selected or the deviation from the regulations, if any, and its justification;
2. Development criteria reference and constraints.
a. Previous drainage studies (i.e., project master plans) for the site in question that influence or are influenced by the drainage design and how the pan will affect drainage design for the site;
b. The effects of adjacent drainage studies; and
c. The drainage impact of site constraints such as streets, utilities, rapid transit, existing structures and development or site plan.
3. Hydrological criteria.
a. Identify design rainfall;
b. Identify runoff calculation method; and
c. Identify detention discharge and storage calculation method.
4. Identify design storm recurrence intervals. Discussion and justification of other criteria or calculation methods used that are not presented in or referenced by the regulations;
5. Hydraulic criteria.
a. Identify various capacity references; and
b. Other drainage facility design criteria used that are not presented in the regulations.
6. Variances from criteria.
a. Identify provisions by section number for which a variance is requested; and
b. Provide justification for each variance requested.
1. Compliance with standards.
b. Major drainageway planning studies; and
c. Development Manual.
1. Hydrologic computation.
a. Land use assumptions regarding the project and adjacent properties;
b. Table including basin ID, basin acreage, weighted runoff coefficient, basin length, time of concentration, minor and major rainfall intensity, minor and major rational runoff, and routed runoff (for major basins if applicable);
c. Supporting calculations for the weighted runoff coefficients and times of concentration (vertical flow path shown on map); and
d. Rational runoff calculations.
2. Hydraulic computations.
a. Gutter capacities with inlet design and spacing;
b. Storm water collection pipe design (based on sub-basin rational flows and HGL/EGL calculations);
c. Storm water trunk line design (based on major basin routed flows and HGL/EGL calculations);
d. Energy dissipation and permanent erosion control devices;
e. Culvert capacities;
f. Open channel design;
g. Check and drop structure design;
h. Detention pond volume and discharge design including emergency spillway; and
i. Downstream outfall capacity to major drainageway.
(3) All calculations required to achieve the final results must be shown in the appendices. All tables, charts and nomographs used in the preparation of this report must also be included in the appendices, each following the computation where first utilized. The hydraulic and energy grade lines must be shown on all construction plan storm profiles. Velocity for storm sewers that discharge to open channels or detention ponds.
(C) Drawing contents. Map(s) of the proposed development at a scale of one inch equals 20 feet to one inch equals 200 feet on a 24-inch by 36-inch drawing shall be included. In addition to the Phase I drawing requirements, the plan shall show the following:
(1) Streets, if available, indicating name, R.O.W. width, flow line width, sidewalk and the like;
(2) Existing drainage facilities and structures, including irrigation ditches, roadside ditches, drainageways, gutter flow directions and culverts. All pertinent information such as material, size, shape, slope and location shall also be included;
(3) Overall drainage area boundary and drainage sub-area boundaries. Generally, off-site basins may be shown on the general location map. In some instances, the City Engineer may require that all affected basins be shown on the drainage plan, in their entirety. A pre-submission conference should be held with the City Engineer prior to submittal;
(4) One hundred-year floodplain for open channels, streams or other natural watercourses not included in the FIRM mapping;
(5) Proposed type of street flow (i.e., vertical or combination curb and gutter), gutter slope and flow directions, and cross pans, if available;
(6) Proposed storm sewers and open drainageways, if available, including inlets, manholes, culverts, other appurtenances and riprap protection; location and (if known) elevation of all existing and proposed utilities affected by or affecting the drainage design; and definition of flow path leaving the development through the downstream properties ending at a major drainageway;
(7) Routing of off-site drainage flow from tributary areas through the development;
(8) Proposed outfall point for runoff from the developed area and facilities to convey flows to the final outfall point without damage to downstream properties;
(9) Routing and accumulation of flows at various critical points for the initial storm run-off and significant changes in flow, and all drainage structures including manholes, inlets, junction boxes, culverts and bridges;
(10) Volumes and release rates for detention storage facilities and information on outlet works and 100-year water line; and
(11) Location and elevations of all existing floodplains affecting the property.
(Ord. 3319, passed 2-22-2005)