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6 <br /> APPENDIX TO INTERGOVERNMENTAL AGREEMENT <br /> FOR ACCOMMODATING SURFACE WATER IN THE <br /> Marshland Flood Control District <br /> BY AND BETWEEN THE City of Everett and <br /> Marshland Flood Control District <br /> In 1994 Snohomish County (COUNTY)contracted with Aqua Terra Consultants to model <br /> the hydrology of the Marshland Watershed. Aqua Terra used the EPA State Hydrological <br /> Simulation Program-FORTRAN (HSPF)model to simulate the hydrology of the watershed area. <br /> In 1997 Marshland Flood Control District (MARSHLAND) had its consultants, most <br /> notably Associated Earth Sciences Inc., use the Aqua Terra report and its own study to evaluate <br /> the increase in sediment discharge based upon Aqua Terra's hydrology model. <br /> The combination of data from these studies, and subsequent analyses using their data, <br /> results in certain figures which carry a degree of credibility with the COUNTY, the City of <br /> Everett (CITY) and MARSHLAND. Those credible data may be summarized as set forth <br /> below. <br /> The entire Marshland Watershed consists of approximately 14,450 acres comprised of <br /> two separate basins. The MARSHLAND (or floodplain)Basin comprises 6,440 acres or 44.6% <br /> of the total watershed. The Hillside (or upland) Basin above MARSHLAND consists of <br /> approximately 8,010 acres or 55.4% of the total watershed. Of these Hillside Basin acres, the <br /> CITY limits include approximately 1,845 acres or 12.7% of the total watershed and 23% of the <br /> Hillside Basin. The remainder of the Hillside Basin is located within COUNTY boundaries <br /> which comprise about 6,165 acres or 42.7% of the total watershed and 77% of the Hillside <br /> Basin. <br /> The Aqua Terra HSPF study indicates the MARSHLAND Basin contributed 49% of the <br /> total watershed flows before the Hillside Basin was developed. The remaining 51% of flows <br /> were contributed by the Hillside Basin. CITY acreage contributed 23% of the Hillside flows <br /> and COUNTY acreage contributed 77%. <br /> Aqua Terra's study also indicates, however, that based upon hillside development <br /> modeled in 1994 and 1997, MARSHLAND Basin is now contributing 44% of current flows, <br /> while the Hillside Basin is contributing 56%. Since the CITY contributes 23% of this 56%, the <br /> CITY's share of flows is approximately 12.88% of total current flows (.23 x .56 = .1288). <br /> Likewise, since the COUNTY contributes 77% of this 56%, the COUNTY's share of flows is <br /> approximately 43.1% of total current flows (.77 x .56 = .431). <br /> APPENDIX TO INTERGOVERNMENTAL AGREEMENT FOR <br /> ACCOMMODATING SURFACE WATER IN THE MARSHLAND <br /> FLOOD CONTROL DISTRICT BY AND BETWEEN THE CITY OF <br /> EVERETT AND MARSHLAND FLOOD CONTROL DISTRICT-PAGE 1 <br /> I7 <br />