Pueblo County Code - Title 16 - Chapter 16.76 General Engineerirng Specifications

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16.76.010 Drainage.

     A. Drainage Criteria. The Pueblo County Drainage Criteria Manual will use a storm duration of six hours for hydrologic computations. A return frequency of five years will be used for determining runoff for minor collection systems (drainage areas less than four hundred (400) acres and peak flows less than five hundred (500) cfs). A return frequency of one hundred (100) years will be used for determining runoff for major collection systems (drainage areas four hundred (400) acres and larger and for all peak flows equal to or exceeding five hundred (500) cfs).
     B. Drainage Control. Each development shall provide for the on-site or off-site detention of excess stormwater runoff from that development and ensure that:
     1. All stormwater storage facilities shall be designed with sufficient capacity to accommodate all runoff caused by the development in excess of the runoff which would have resulted from the site if left in its natural, existing or undeveloped condition;
     2. No development shall cause downstream property owners, water courses, channels or conduits to receive stormwater runoff from proposed developments at a higher peak flow rate than would have resulted from the same storm event occurring over the site of proposed development with the land in its existing, natural or undeveloped condition;
     3. The development will not prevent the unimpeded flow of natural water courses;
     4. All low points within the development area are ensured adequate drainage;
     5. The drainage system shall be designed to consider the drainage basin as a whole and shall accommodate not only runoff from the proposed development area, but also, where applicable, the system shall be designed to accommodate the runoff from those areas adjacent to and upstream from the subdivision itself, as well as its effects on lands downstream;
     6. In areas in which calculations have been developed, by the U.S. Geological Survey, Soil Conservation Service, or County studies or reports, those figures shall be used for purposes of calculation. All proposed surface-drainage structures shall be indicated.
     All appropriate designs, details, and dimensions necessary to clearly explain proposed construction materials and elevations shall be included in the drainage plans.
     C. Detention Storage. All development must restore runoff characteristics to at least natural conditions. The following formula is an example to calculate the volume of detention required:
     V = Rd - Rn - Ros - S - GW
     V = the change in volume (in cubic feet per second) from the site. This is the base volume of excess stormwater flows that would result from the development.
     Rd = the volume of stormwater runoff (in cubic feet per second) flowing from the site after its development. This determination shall include runoff from pervious and impervious surfaces, changes in areas of forest, changes in soils due to compaction, and changes in the time of concentration, for a one hundred (100) year storm of twenty-four (24) hour duration.
     Rn = the volume of stormwater runoff (in cubic feet per second) flowing from the site in its natural state. This determination shall include runoff from the site with its natural cover, grassland, or woodland for a one hundred (100) year storm of twenty-four (24) hour duration. Farm fields shall be calculated as grassland.
     Ros = the volume of stormwater runoff (in cubic feet per second) flowing onto the site from upstream properties in their present state of development for a one hundred (100) year storm of twenty-four (24) hour duration.
     S = the change in capacity (in cubic feet per second) of the natural on-site detention areas of the site. This indicates any drainageways, small depressional areas, or other areas which would naturally retain water during a one hundred (100) year storm of twenty-four (24) hour duration.
     (This calculation may carry either a plus or minus value.)
     GW = the change in subsurface flows due to dewatering techniques which would add to the total surface water runoff during a one hundred (100) year storm of twenty-four (24) hour duration. Included here are dewatering devices such as drain tiles, curtain drains, or sump pumps. (This calculation may carry either a plus or minus value.)

     A detention storage typical is presented following these Regulations.

16.76.020 Floodplain.

     A. Definition. A floodplain or flood-prone area is any land susceptible to being inundated as the result of a flood, including the area of land over which floodwater would flow from the spillway of a reservoir.  100-Year Floodplain is the area of land susceptible to being inundated as a result of the occurrence of a one-hundred-year flood as designated by the Federal Emergency Management Agency.
     B. Subdivision.
     1. Subdivision applications, including subdivision variance, incorporating land within a floodplain shall be accompanied by a floodplain hydrology report, prepared by a registered professional engineer, which establishes the water surface elevation of a flood with a one percent chance of occurring in any given year.
     2. The subdivision plat shall show the contour and elevation of the floodplain which shall be identified as the "Special Flood Hazard Area--100-Year Floodplain" or similar informational notation. A plat note shall also appear on the plat which advises that "A Flood Hazard Area Development Permit and/or compliance with additional floodplain regulations may be required prior to development in the Flood Hazard Area" or similar informational notation.
     C. Utilities.
     Comply with Title 17 Land Use Division I. Zoning Chapter 17.04 GENERAL PROVISIONS AND DEFINITIONS Section 17.040.040 Definitions and Chapter 17.108 FLOOD HAZARD AREA REGULATIONS.

16.76.030 Erosion.

     A. All measures necessary to minimize soil erosion and to control sedimentation in the disturbed land shall be provided.
     Specifically, the design and implementation of the proposed measures shall ensure:
     1. That any development is designed and executed in a manner which will save and protect as much of the desirable native vegetation as possible;
     2. That a reclamation plan for revegetation on all disturbed areas be guaranteed;
     3. That all cuts and fills are adequately designed and engineered to prevent detachment and transportation of soil particles from slope.
     When possible, developments should consider fitting the buildings and streets to the natural topography. Slopes greater than 3:1 are undesirable, while slopes of 6:1 are the most desirable.
     Developers are required to consult the Soil Conservation Service regarding soil limitations for the intended land use and may request assistance in preparing conservation plans for developing areas.
     B. Tables are presented following these regulations as a graphic summary of erosion and sedimentation control measures. Asterisk(s) identify measures which may effectively control the problem area.

16.76.040 Mineral resource area.

     Pursuant to the Master Plan for extraction, Pueblo County shall reserve the right to require the extraction of commercial mineral deposits prior to development of designated mineral resource areas.
     It is the purpose of these regulations to regulate development in mineral resource areas in order to minimize significant hazards to public health and safety, and to insure the availability to the public of necessary and useful minerals.

16.76.050 Geologic reports.

     Each report should include definite statements concerning the following matters:
     A. Location and size of subject area and its general setting with respect to major geographic and geologic features;
     B. Author or entity who did the geologic mapping upon which the report is based and when the mapping was done;
     C. Any other types of investigations made by the geologist and, where pertinent, reasons for doing such work;
     D. Topography and drainage in subject area;
     E. Abundance, distribution and general nature of exposures of earth materials within the area;
     F. Location and description of any geologic hazards with the area. Geologic hazards include, but are not limited to: avalanches, landslides, rock falls, mudflows, unstable or potentially unstable slopes, seismic effects, radioactivity, ground subsidence, expansive soils and rocks accelerated erosion areas, and high groundwater areas;
     G. The location of test holes and other specific sources of subsurface information;
     H. Deposits related to recent floods (e.g., talus aprons, debris ridges, canyon-bottom trash);
     I. Percolation rates (when applicable) present and expected;
     J. Recommended building foundation types for proposed use;
     K. Recommended drainage structures;
     L. Justification of methodology;
    M. The Geologic Report shall be prepared by a Professional Geologist, according to the Colorado Revised Statutes (CRS) Section 34-1-201. Definitions (3) "Professional Geologist" and Section 34-1-202. Reports Containing Geologic Information.