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TECHNICAL MEMORANDUM <br /> July 13, 1995 <br /> Page 13 <br /> Cleaning and repair provisions are tantamount to a good overall program. A wide variety of <br /> arrangements exists to accommodate cleaning, repairs, and system maintenance. Some <br /> communities perform all, or essentially all, of these tasks with their own staff and equipment. <br /> Others perform none, and either contract with private firms or establish interlocal <br /> arrangements with neighboring jurisdictions for support. And many communities blend <br /> maintenance functions, some in -house and some by others under contract for service. <br /> Adequate enforcement of drainage standards, criteria, policies, procedures, and program goals <br /> is appropriate for optimum system performance. Much of this can be done during the <br /> planning, design, and construction phases of new projects. Another, challenge has been to <br /> enforce the requirements during the ongoing operation phase; in other words, during the many <br /> years that the facility is in operation. Some jurisdictions have rigorous requirements and <br /> enforcement provisions. As mentioned above, King County has a comprehensive program <br /> that even includes civil penalties for noncompliance, including water quality degradation. <br /> Medford may want to consider an appropriate level of enforcement for both water quantity <br /> and water quality aspects of the stormwater management program. <br /> RECOMMENDED DRAINAGE STANDARDS <br /> The following subsections briefly summarize the types of recommended drainage standards <br /> and related issues for the city of Medford. These recommendations will be updated and <br /> finalized based upon further information regarding hydraulics/hydrology and alternatives <br /> evaluation developed during the master planning effort and from review comments from city <br /> staff. <br /> Intensity- Duration - Frequency Curves <br /> The current update to the Drainage Master Plan included examination of the IDF curves as <br /> defined in the existing master plan. The purpose of the study was to determine whether the <br /> curves required updating. New curves were developed based upon the historical rainfall <br /> record from several recording stations in the Medford area. The new curves showed an <br /> approximate 50 percent decrease from the original curves in the maximum rainfall intensity <br /> for storm events less than one hour in duration. Upon further analysis and discussions with <br /> city staff, it was decided to continue using the existing IDF curves. Based upon Brown and <br /> Caldwefl'sunalysis, the existing curves provide an additional level of- floodinprotection over <br /> and above what the new curves would have provided. The existing curves have served the <br /> city well for more than 20 years; lets not fix what is not broken. <br /> On -site versus Off -site Detention /Retention <br /> The issue of on -site versus offsite detention or retention is typically one of the most <br /> controversial components of stormwater drainage management. Many jurisdictions require <br /> DRAFT <br /> J <br /> \21 1 1 ask1W n31. cug <br />