<div class="chunk-title">Sec. 31-9. - Stormwater outlet protection.</div>
<div class="chunk-content">
            <p class="incr0">
               (a)
               </p>
            		
            <p class="content1">
               <span class="ital">Intent.</span> Stream banks and channels downstream from any land-disturbing activity shall be protected
               from increased degradation by accelerated erosion caused by increased velocity of
               runoff from the land-disturbing activity.
               </p>
            		
            <p class="incr0">
               (b)
               </p>
            		
            <p class="content1">
               <span class="ital">Performance standard.</span> Persons shall conduct land-disturbing activity so that the post construction velocity
               of the ten-year storm runoff in the receiving watercourse to the discharge point does
               not exceed the greater of:
               </p>
            		
            <p class="incr1">
               (1)
               </p>
            		
            <p class="content2">
               The velocity established by the maximum permissible velocities table set out within
               this subsection; or
               </p>
            		
            <p class="incr1">
               (2)
               </p>
            		
            <p class="content2">
               The velocity of the ten-year storm runoff in the receiving watercourse prior to the
               development.
               </p>
            		
            <p class="b2">
               If condition (1) or (2) of this paragraph cannot be met, then the receiving watercourse
               to and including the discharge point shall be designed and constructed to withstand
               the expected velocity anywhere the velocity exceeds the "prior to development" velocity
               by ten percent.
               </p>
            <p class="bc2">
               <span class="bold">Maximum Permissible Velocities Table</span>
               </p>
            <p class="p0">
               The following is a table for maximum permissible velocity for storm water discharges
               in feet per second (F.P.S.) and meters per second (M.P.S.):
               
               <div>
                  <div class="" style="width:100%">
                     <table class="thead1 table  left" cellpadding="3" cellspacing="0" border="1" rules="all" style="font-size:11px;">
                        <colgroup class="std">
                           <col width="60%">
                           <col width="20%">
                           <col width="20%">
                        </colgroup>
                        <tbody>
                           <tr>
                              <td class=" top ">
                                 Material
                                 </td>
                              <td class=" top ">
                                 F.P.S.
                                 </td>
                              <td class=" top ">
                                 M.P.S.
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Fine sand
                                 <br>
                                 (noncolloidal)
                                 </td>
                              <td class=" top ">
                                 2.5
                                 </td>
                              <td class=" top ">
                                 0.8
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Sandy loam
                                 <br>
                                 (noncolloidal)
                                 </td>
                              <td class=" top ">
                                 2.5
                                 </td>
                              <td class=" top ">
                                 0.8
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Silt loam
                                 <br>
                                 (noncolloidal)
                                 </td>
                              <td class=" top ">
                                 3.0
                                 </td>
                              <td class=" top ">
                                 0.9
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Ordinary firm loam
                                 </td>
                              <td class=" top ">
                                 3.5
                                 </td>
                              <td class=" top ">
                                 1.1
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Fine gravel
                                 </td>
                              <td class=" top ">
                                 5.0
                                 </td>
                              <td class=" top ">
                                 1.5
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Stiff clay
                                 <br>
                                 (very colloidal)
                                 </td>
                              <td class=" top ">
                                 5.0
                                 </td>
                              <td class=" top ">
                                 1.5
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Graded, loam to cobbles
                                 <br>
                                 (colloidal)
                                 </td>
                              <td class=" top ">
                                 5.0
                                 </td>
                              <td class=" top ">
                                 1.5
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Alluvial silts
                                 <br>
                                 (noncolloidal)
                                 </td>
                              <td class=" top ">
                                 3.5
                                 </td>
                              <td class=" top ">
                                 1.1
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Alluvial silts
                                 <br>
                                 (colloidal)
                                 </td>
                              <td class=" top ">
                                 5.0
                                 </td>
                              <td class=" top ">
                                 1.5
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Coarse gravel
                                 <br>
                                 (noncolloidal
                                 </td>
                              <td class=" top ">
                                 6.0
                                 </td>
                              <td class=" top ">
                                 1.8
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Cobbles and shingles
                                 </td>
                              <td class=" top ">
                                 5.5
                                 </td>
                              <td class=" top ">
                                 1.7
                                 </td>
                           </tr>
                           <tr>
                              <td class=" top ">
                                 Shales and hard pans
                                 </td>
                              <td class=" top ">
                                 6.0
                                 </td>
                              <td class=" top ">
                                 1.8
                                 </td>
                           </tr>
                           <tr>
                              <td colspan="3" class=" top ">
                                 Sourceâ€”Adapted from recommendations by Special Committee on Irrigation Research, American
                                 Society of Civil Engineers, 1926, for channels with straight alignment. For sinuous
                                 channels, multiply allowable velocity by 0.95 for slightly sinuous, by 0.9 for moderately
                                 sinuous channels, and by 0.8 for highly sinuous channels.
                                 </td>
                           </tr>
                        </tbody>
                     </table>
                  </div>
                  <p>&nbsp;</p>
               </div>
               
            <p class="incr0">
               (c)
               </p>
            		
            <p class="content1">
               <span class="ital">Acceptable management measures.</span> Measures applied alone or in combination to satisfy the intent of this section are
               acceptable if there are no objectionable secondary consequences. The county recognizes
               that the management of stormwater runoff to minimize or control downstream channel
               and bank erosion is a developing technology. Innovative techniques and ideas will
               be considered and may be used when shown to have the potential to produce successful
               results. Some alternatives, while not exhaustive, are to:
               </p>
            		
            <p class="incr1">
               (1)
               </p>
            		
            <p class="content2">
               Avoid increases in surface runoff volume and velocity by including measures to promote
               infiltration to compensate for increased runoff from areas rendered impervious;
               </p>
            		
            <p class="incr1">
               (2)
               </p>
            		
            <p class="content2">
               Avoid increases in stormwater discharge velocities by using vegetated or roughened
               swales and waterways in place of closed drains and high velocity paved sections:
               </p>
            		
            <p class="incr1">
               (3)
               </p>
            		
            <p class="content2">
               Provide energy dissipaters at outlets of storm drainage facilities to reduce flow
               velocities to the point of discharge;
               </p>
            		
            <p class="incr1">
               (4)
               </p>
            		
            <p class="content2">
               Protect watercourses subject to accelerated erosion by improving cross sections and/
               or providing erosion-resistant lining; and
               </p>
            		
            <p class="incr1">
               (5)
               </p>
            		
            <p class="content2">
               Upgrade or replace the receiving device structure or watercourse such that it will
               receive and conduct the flow to a point where it is no longer subject to degradation
               from the increased rate of flow or increased velocity.
               </p>
            		
            <p class="incr0">
               (d)
               </p>
            		
            <p class="content1">
               <span class="ital">Exceptions.</span> This rule shall not apply where it can be demonstrated to the county that storm water
               discharge velocities will not create an erosion problem in the receiving watercourse.
               </p>
            		
            <p class="historynote0">
               (Ord. No. 2008-18, 11-17-2008; Ord. No. 2021-10, 10-18-2021)
               </p></div>