Flood response: Mecklenburg County, NC

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" rowspan="2" width=185 BGCOLOR="#FFFFFF" TEXT="#080000"> <div> <A HREF="index.htm" TARGET="_top" TITLE="David Ford Consulting Engineers"><U><B><IMG SRC="0d058960.png" border=0 width="88" height="150" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></B></U></A></div> <bR> <div>    <FONT SIZE="1" COLOR="#000000" FACE="Verdana" > </FONT></div> <div> <B> <TABLE BORDER="0" CELLPADDING="4" CELLSPACING="1" WIDTH="156" BORDERCOLORLIGHT="#FFFFFF" BORDERCOLORDARK="#FFFFFF" FRAME="VOID" RULES="NONE" HSPACE="0" VSPACE="0" > <tR> <tD VALIGN=TOP HEIGHT= 27 WIDTH="146"><div> David Ford Consulting Engineers, Inc.</div> </tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 27 ><NOBR><div> 2015 J Street, Suite 200</div> <div> Sacramento, CA 95811</div> </NOBR></tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 27 WIDTH="146"><div> tel: 916.447.8779</div> <div> fax: 916.447.8780</div> </tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 27 WIDTH="146"><div> <A HREF="mailto:support@ford-consulting.com" TARGET="_top" TITLE="mailto:support@ford-consulting.com"><U>support@ford-consulting.com</U></A></div> </tD> </tR> </TABLE></B></div> <div>    </div> <bR> <div> <A HREF="index.htm" TARGET="_top" TITLE="David Ford Consulting Engineers"><U>Home</U></A></div> <div> <A HREF="id461.htm" TARGET="_top" TITLE="About us"><U>About us</U></A></div> <div> <A HREF="news.htm" TARGET="_top" TITLE="News"><U>News</U></A></div> <div> <A HREF="hydrologic_engineering.htm" TARGET="_top" TITLE="Hydrologic engineering"><U>Hydrologic engineering</U></A></div> <div> <A HREF="water_resource_planning.htm" TARGET="_top" TITLE="Water resource planning"><U>Water resource planning</U></A></div> <div> <A HREF="flood_economic_and_risk_analyses.htm" TARGET="_top" TITLE="Flood economic and risk analyses"><U>Flood economic/risk analyses</U></A></div> <div> <A HREF="flood_warning.htm" TARGET="_top" TITLE="Flood warning"><U>Flood warning</U></A></div> <div> <A HREF="decision_support_system_development.htm" TARGET="_top" TITLE="Decision support system development"><U>Decision support systems</U></A></div> <bR> </td> <td valign="top" colspan=2 height=40 BGCOLOR="#3366CC" TEXT="#080000" bgproperties="fixed" background="14400980ezthpx.png"> <div> <B>Flood response: Mecklenburg County, NC</B></div> <div> </div> </td> </tr><tr> <td valign="top" height=440 colspan=2 BGCOLOR="#FFFFFF" TEXT="#080000" bgproperties="fixed" background="06c00962egerdp.png"> <div> <B> <TABLE BORDER="0" CELLPADDING="2" CELLSPACING="1" WIDTH="547" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#808080" FRAME="BOX" RULES="ALL" HSPACE="0" VSPACE="0" > <tR> <tD VALIGN=TOP COLSPAN=3 BGCOLOR=#CC0000 HEIGHT= 16 WIDTH="537"><div> <B>Situation</B></div> </tD> </tR> <tR> <tD VALIGN=TOP COLSPAN=3 HEIGHT= 359 WIDTH="537"><div> Mecklenburg County initiated development of a flood warning system by installing automated rainfall and water level sensors and companion data transmission, management, and visualization hardware and software. The County intended to take steps to expand this, providing other components required for a complete system. However, they wondered if the system would yield benefits that exceeded the cost. They also worried about the liability and risk associated with this.</div> <DIV ALIGN="LEFT"></DIV> <div> <IMG SRC="164b8cf0.png" border=0 width="440" height="207" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <div> <I>Flooding in Mecklenburg County (Photo courtesy of Mecklenburg County, NC)</I></div> <bR> </tD> </tR> <tR> <tD VALIGN=TOP COLSPAN=3 BGCOLOR=#339933 HEIGHT= 16 WIDTH="537"><div> <B>Action</B></div> </tD> </tR> <tR> <tD VALIGN=TOP COLSPAN=3 HEIGHT= 295 WIDTH="537"><div> We first identified a representative sample of flood prone areas, using available GIS and stormwater management studies. We then developed and applied a procedure for estimating expected warning lead time. This relies on recursive simulation, with existing watershed and channel models, with increments of data from a set of historical or design storm events. In each case, the earliest time of detection of exceedence of a flood threshold is noted, and the resulting values are weighted by probability to compute an expected value of the maximum possible lead time. This value is reduced to account for the time lost disseminating information. </div> <div> With this method, we found that the expected lead time for areas within the FEMA regulated floodplains averaged about 90 minutes, and upstream of the FEMA regulated floodplains, it was less than 10 minutes. Consequently, we recommended that the County focus on flood warning in the FEMA floodplains, as the lead times elsewhere were too small to allow any significant response prior to flooding.</div> <div> We also conducted research to identify the liability associated with operation of a flood warning system. Briefly, we concluded that if the County follows documented procedures, provides adequate training, and performs required maintenance, the liability associated with flood warning can be minimized.</div> </tD> </tR> </TABLE></B></div> <bR> <bR> </td> </tr></table></body>