(A) Preliminary Drainage Report. A Preliminary Drainage Report shall be required for commercial and residential subdivisions, and public works construction projects. The Preliminary Drainage Report shall be submitted with the Preliminary Subdivision Plat or with the first plans submitted, and shall be structured using the following report outline for major headings, and contain the described information, as a minimum. Sections that are not appropriate or necessary for the application shall still be included in the document with a statement that the section was not applicable. This outline also applies to the Final Drainage Report described in division (B) of this section. Submittal requirements specific to the Preliminary Drainage Report will be identified as such.
(1) Introduction. This section shall define the purpose of the report, the location of the project (including location and vicinity maps), a description of the hydrologic setting, and an overview of the proposed drainage scheme for the project.
(2) Mapping and survey information. This section shall describe the source and date of field survey control data, and the date and source of topographic mapping used as a basis for the project. All field survey control shall be done using North American Datum of 1983 (NAD 83) State Plane Coordinates for horizontal control, and North American Vertical Datum of 1988 (NAVD 88) for vertical control. Field survey control shall be tied into the field survey control network used for the PDMP.
(a) Watershed map. A map shall be prepared of the entire watershed that contributes runoff to and from the site. The map shall be based on the best available topography of record for the offsite watershed. The watershed map shall show the boundaries of all watersheds that affect the project site. Watersheds with a 100-year peak discharge of 10 cfs or greater shall have concentration points defined where runoff enters and leaves the site. Labels for sub-basins shall match those used in the hydrology models.
(b) Existing condition site map. An existing condition site topographic map shall be prepared for the project site with existing channels, ditches, structures, existing low areas that currently detain storm water and sheet flow areas clearly identified. The topographic map, as a minimum, shall depict two-foot contours. The Public Works Department may require a one-foot contour interval. The submitter shall verify the topographic requirements for the site with the town prior to beginning preparation of the site map. All areas where the existing ground slope is greater than 15% shall be identified. Existing condition drainage basin and sub-basin boundaries shall be shown, as well as peak discharges for the 2-, 10- and 100-year storms at defined drainage concentration points. FEMA 100-year floodplain and floodway limits of record shall be shown. The floodplain limits for major watercourses for the future condition 100-year flood shall be defined as called for in §§ 152.50 - 152.53, and shown on the map. Major watercourses are those with an existing condition 100-year peak discharge of 50 cfs or greater. Existing and future condition peak discharges are to be taken from the PDMP, or generated as a part of the Preliminary Drainage Report if the watershed is not covered in sufficient detail in the PDMP.
(c) Developed condition site map. A developed condition site plan shall be prepared including existing condition topography, proposed site grading, and street flow patterns. Any proposed channels, storm sewers, catch basins and culverts, and detention and/or retention facilities are to be sized using approximate methods and shown.
(d) Hydrologic modeling calculations. The hydrologic modeling assumptions, parameters and results shall be documented in the text and appendix attachments in general conformance with the report outline for hydrology in ADWR Requirements for Flood Study Technical Documentation (9997) (TDN).
(4) Floodplain delineation. This section shall be based on the policies and methodologies set forth in §§ 152.50 - 152.53. This section shall document hydraulic calculations for floodplain and floodway delineations. The hydraulic modeling assumptions, parameters and results shall be documented in the text and appendix attachments in general conformance with the TDN report outline for hydraulics.
(5) Stormwater storage. This section shall be based on the policies and methodologies set forth in §§ 152.60 - 152.62. This section shall document the sizing calculations for detention and/or retention facilities. Documentation for the Preliminary Drainage Report shall locate and rough-size proposed basins. Documentation for the Final Drainage Report shall include stage/discharge/storage rating curves for outlet structures for detention basins, and the volume of water to be stored, the locations of storage, and the methods for disposal for retention basins.
(6) Open channel design. This section shall be based on the policies and methodologies set forth in §§ 152.70 - 152.73. This section shall document the sizing and hydraulic calculations for proposed open channels. Documentation for the Preliminary Drainage Report shall locate and rough-size proposed open channels. Documentation for the Final Drainage Report shall include printouts of the input and output from hydraulic computer modeling, and summary tables of results including design discharge, flow depths, velocities, Froude number, slope, roughness coefficients, energy gradient, and critical depth.
(7) Culverts and storm drains. This section shall be based on the policies and methodologies set forth in §§ 152.80 - 152.83. This section shall document the sizing of culverts, storm drains, catch basins, and scuppers. Documentation for the Preliminary Drainage Report shall locate and rough-size proposed culverts, storm drains and catch basins. Documentation for the Final Drainage Report shall include printouts of the input and output from computer modeling, hand calculation sheets, and summary tables of results.
(8) Erosion and sedimentation. This section shall be based on the policies and methodologies set forth in §§ 152.90 - 152.92. This section shall document the sizing of erosion and sedimentation control measures for bank and bed protection for open channels, inlet and outlet scour protection for culverts, storm drains and bridges, grade control structures, and sedimentation basins. Documentation for the Preliminary Drainage Report shall discuss anticipated erosion control and sedimentation problem areas, as well as proposed solutions. Documentation for the Final Drainage Report shall include printouts of the input and output from erosion computer modeling, and summary tables of results corresponding to each structural component defined in divisions (A)(4) - (A)(6) of this section.
(9) Results and recommendations. This section shall summarize and discuss the results of the study. The key drainage components and their intended function shall be listed and described. The drainage patterns downstream of the project shall be described and the possible effects of runoff from the project on downstream areas discussed. Measures proposed to mitigate possible effects shall be described and related to the drainage components and their intended function.
(B) Final Drainage Report. A Final Drainage Report must be submitted for all commercial and residential subdivisions, and public works construction projects, in conjunction with the submittal of construction plans for review. The Final Drainage Report shall be an updated version of the preliminary drainage report. The update shall include all information from the Preliminary Drainage Report, revised to reflect the final design condition, including final, detailed design calculations for all drainage components, and revised developed condition hydrology models and results. The Final Drainage Report shall be coordinated with the final construction plans using nomenclature common to the report and plans. Sections of the report outline that are not appropriate or necessary for the application shall be included with a statement that the section was not applicable. Digital copies of all input and output files from software modeling shall be included on electronic media in the final report.
(C) Drainage Memorandum.
(1) A Drainage Memorandum is a simplified report suitable for addressing drainage concerns for the development or redevelopment of a single commercial or industrial lot. If the total contributing watershed is less than 160 acres in area and the 100 year peak discharge is less than 10 cfs, simple Rational Method calculations may be applied to estimate pre- and post-development discharges for design of channels, pipes, and other drainage facilities. Runoff volumes, and detention or retention requirements, shall be estimated in accordance with the requirements of §§ 152.30 - 152.39 and §§ 152.60 - 152.62. The memorandum can be in the form of a separate document, or included on the construction-grading plan. The minimum information to be contained in the memorandum or on the construction-grading plan is:
(a) Drainage area.
(b) Pre-development and post-development peak discharges and runoff volumes.
(c) Detention/retention basin design calculations.
(d) Detention/retention volume required and provided.
(e) Design hydraulic calculations for discharge structures.
(f) Critical hydraulic control elevations.
(g) 100-year 24-hour storm ponding limits.
(2) The detention or retention basins are to be clearly identified on the plan, fully dimensioned with the high water elevation identified, and cross section views provided as needed for clarity. Any retention basin volume calculations are to be easily verified using the plan details.
(D) Site drainage evaluation. The Public Works Department will perform a Site Drainage Evaluation at the time an application is made for a residential building permit or, if no building permit is required, when the grading plan is submitted. The Public Works Department will review the residential building site plan for conformance with the town requirements. All drainage and grading of individual residential lots must be done in accordance with the town requirements in §§ 152.110 - 152.130. The Public Works Department will evaluate all grading and drainage not related to the foundation of a structure. In general, the following will be required:
(1) All residential grading will be required to have a minimum setback of two feet from property lines (more may be required depending on the height of the cut or fill).
(2) All fill shall be compacted to a minimum of 90% of maximum dry density.
(3) All fill slopes greater than 2:1 shall be required to have a licensed civil or geotechnical engineer certify the slope for stability.
(4) Fill slopes in excess of 3:1 and cut slopes in excess of 2:1 shall have appropriate erosion control measures applied, such as riprap or designed vegetation cover.
(5) Existing natural drainages may not be obstructed or relocated without plans approved by the Public Works Department. The point where such drainages enter and exit the property must not be changed. Nothing may be done on the property to significantly change the velocity of flow where storm water exits the site.
(6) As the town requirements are revised periodically, additional requirements may be imposed.
(7) Individual residential lots must have a final inspection of site grading prior to receiving final inspection approval.
(E) Grading and drainage permit. A grading and drainage permit is required for any commercial, industrial or residential lot where a new structure is to be constructed or, proposed excavation or embankment exceeds a volume of 50 cubic yards. The Town Grading Permit Assistance Form and an example of a grading and drainage plan for a residential lot are shown on Figures 2.1 through 2.3 in § 152.18. A Grading and Drainage Plan must accompany every request for a grading and drainage permit. The following additional submittal requirements are based on whether the parcel in question has an offsite watershed that drains to the site that will be affected by the construction:
(1) Offsite watershed with Q100 less than 10 cfs: In addition to the Grading and Drainage Plan, submit substantiation that this requirement is met, and submit a Drainage Memorandum.
(2) Offsite watershed with Q100 greater than 10 cfs: In addition to the Grading and Drainage Plan, submit a Preliminary Drainage Report in accordance with division (A) of this section.
(F) Floodplain Development Permit.
(1) The Floodplain Administrator is the Public Works Director or their designee, who shall administer and enforce this regulation. A Floodplain Development Permit shall be obtained from the Public Works Department prior to commencing any new structure, proposed addition, alteration or change of any building, structure, land or other use within a 100-year floodplain, except as exempted by applicable law. A 100-year floodplain includes any 100-year floodplain designated and adopted by FEMA, or the flood limits resulting when a watercourse or contributing watershed has flows greater than 50 cfs during a 100-year storm event, whether for existing or anticipated future conditions. Refer to §§ 152.50 - 152.53 for floodplain management policies.
(2) The Public Works Department may place a time limit on the Floodplain Development Permit and any other conditions or restrictions designed to reduce or eliminate potential hazards to life or property. As stated by town ordinance and FEMA regulations, absolutely no construction or fill may be placed in the regulatory 100-year floodway without meeting the appropriate requirements of division (G) of this section.
(3) The applicant may be required to execute deed restrictions running with the land or to post performance bonds, assurances or other security to guarantee the performance of the conditions and restrictions imposed.
(4) The applicant shall submit any information the Public Works Department considers necessary in making determinations required by this regulation. The applicant may also be required to provide certification by a Professional Civil Engineer, licensed to practice in the State of Arizona, that all requirements of the Floodplain Development Permit have been met.
(G) FEMA CLOMR, LOMR and PMR.
(1) A FEMA CLOMR, LOMB or PMR is required for any change to a FEMA designated 100-year floodplain or floodway map proposed as part of a residential or commercial subdivision, or any Public Works Improvement Project. The three terms are defined as follows:
Conditional Letter of Map Amendment (CLOMA) A letter from FEMA stating that a proposed structure that is not to be elevated by fill would not be inundated by the base flood if built as proposed.
Letter of Map Amendment (LOMA) A letter from FEMA stating that an existing structure or parcel of land that has not been elevated by fill would not be inundated by the base flood.
Conditional Letter of Map Revision Based on Fill (CLOMR-F) A letter from FEMA stating that a parcel of land or proposed structure that is to be elevated by fill would not be inundated by the base flood if fill is placed on the parcel as proposed or the structure is built as proposed.
Letter of Map Revision
Based on Fill (LOMR-F) A letter from FEMA stating that an existing structure or parcel of land that has been elevated by fill would not be inundated by the base flood.
Based on Fill (LOMR-F) A letter from FEMA stating that an existing structure or parcel of land that has been elevated by fill would not be inundated by the base flood.
(2) If, in the opinion of the Public Works Department, a proposed project will have an effect on a FEMA designated floodplain or floodway, then the party creating the need for the CLOMR must apply for a CLOMR. A LOMR may not be applied for without an approved CLOMR and as constructed plans of the improvements. The applicant must prepare a CLOMR submittal, and subsequently a LOMR submittal, in conformance with FEMA requirements and ADWR TDN requirements. The approval and support of the Public Works Department must be received in writing prior to submittal of the CLOMR or LOMR package to FEMA for review and possible approval. The applicant is responsible for payment of all applicable submittal and review fees. FEMA forms and instructions for CLOMR, LOMR and PMR submittals can be found on the FEMA Internet site at http://www.fema.gov/mit/tsd/EN_main.htm. The ADWR TDN state standard document can be found on the ADWR Internet site at: http://www.water.az.gov/publications/formsnpubs.htm.
(H) FEMA CLOMA, LOMA, CLOMR-F, and LOMR-F.
(1) A FEMA CLOMA, LOMA, CLOMR-F or LOMR-F is required for removal of a parcel of land or a structure from a FEMA designated 100-year floodplain. The four terms are defined as follows:
Letter of Map Amendment (LOMA) A letter from FEMA stating that an existing structure or parcel of land that has not been elevated by fill would not be inundated by the base flood.
Conditional Letter of Map Revision Based on Fill (CLOMR-F) A letter from FEMA stating that a parcel of land or proposed structure that is to be elevated by fill would not be inundated by the base flood if fill is placed on the parcel as proposed or the structure is built as proposed.
Letter of Map Revision
Based on Fill (LOMR-F) A letter from FEMA stating that an existing structure or parcel of land that has been elevated by fill would not be inundated by the base flood.
Based on Fill (LOMR-F) A letter from FEMA stating that an existing structure or parcel of land that has been elevated by fill would not be inundated by the base flood.
(2) If an applicant desires to remove a parcel of land or a structure located within the 100-year floodway fringe from the necessity to pay for flood insurance, then the applicant must obtain either a LOMA or LOMR-F. Neither a LOMA nor LOMR-F for a new structure may be applied for without an approved CLOMA or CLOMR-F and a FEMA Elevation Certificate. The applicant must prepare a CLOMA, LOMA, CLOMR-F, or LOMR-F submittal package in conformance with FEMA requirements and ADWR TDN requirements. The approval and support of the Public Works Department must be received in writing prior to submittal to FEMA for review and possible approval. The applicant is responsible for payment of all applicable submittal and review fees. FEMA forms and instructions for CLOMA, LOMA, CLOMR-F, or LOMR-F submittals can be found on the FEMA Internet site at: http://www.fema.gov/mit/tsd/EN_main.htm. The ADWR TDN state standard can be found on the ADWR Internet site at: http://www.water.az.gov/publications/formsnpubs.htm.
(I) FEMA Elevation Certificate. The FEMA Elevation Certificate applies to all commercial, industrial and residential lots where structures exist or are proposed within the FEMA regulatory 100-year floodplain. The Elevation Certificate is to be used to provide elevation information necessary to ensure compliance with town floodplain management ordinances, to determine the proper insurance premium rate, and to support a request for a LOMA or a LOMR-F. Applicants submitting for a Floodplain Development Permit, or a CLOMA, LOMA, CLOMR-F or LOMR-F must also submit an Elevation Certificate to the Public Works Department. The FEMA Elevation Certificate form and instructions can be found on the FEMA Internet site at: http://www.fema.gov/mit/tsd/DL_elcrt.htm.
(Res. 1637, passed 2-28-02; Am. Res. 2871, passed 9-17-15; Am. Ord. 872, passed 9-17-15)