Laserfiche WebLink
Ordinance Section 23-11-230 B. Specifically, in addition to other violations, we believe that <br />the GUA Reports shows that the Everist Mine has caused excessive increases in flood <br />heights on his property, has altered the natural floodplain which accommodated flood <br />waters historically, and that mine structures have resulted in flood barriers which have <br />unnaturally diverted flood waters and/or have increased flooding on other lands, <br />specifically Mr. Bachofer's property. See § 23-11-230 B. 1., 3., and 5., Weld County Code. <br />The salient results of the 2015 GUA Study indicate the following: <br />Results of the model simulations support the historical and current observations <br />that construction activities at the Everist mine have not only altered the hydrologic <br />regime of the South Platte River but have also changed the morphology and <br />topography of the original floodplain on the west side of the river causing a flow <br />constriction. Storm flows, which in the past could spread and dissipate across the <br />west bank pre -mining flood plain and have no effect on the Bachofer property on <br />the east side, now flood his land. <br />Modeling results from GUA indicate a significant difference (an increase of <br />approximately 2 feet) in surface water elevations in the vicinity of the Bachofer <br />property between pre -mining anfl existing mining surface topography. <br />• Model simulations using the 5 -year event (7,900 cfs) indicate flood levels are now <br />close to the 100 year event previously determined by the Flood Insurance Study <br />(FIS) for the Town of Fort Lupton (USDH and UD, 1978). <br />Modeling results indicate that existing mining conditions (based on the 2008 aerial <br />survey conducted by L.G. Everist) result in a maximum change of approximately 2 <br />feet in the water surface elevation compared to pre -mining conditions for the 100 - <br />year flow event. At cross-section 3193.73, which transects the Bachofer property, <br />there is 1.86 -foot change in water surface between these topographic surfaces for <br />the 100 -year flood event. <br />• The modeled surface water elevation for the 100 -year event using the 2008 mining <br />surface is 4875.81 and is well above the previously established 100 -year flood plain <br />elevation of 4874 determined by Weld County. <br />Model simulations were also conducted for lower flows that include the 5 and 10 - <br />year events. The 5 -year event (7,900 cfs) approximates flow at the Bachofer <br />property which has been recently flooding the lower level of his house. The 5 -year <br />event water surface (4873.91 feet) for current mining conditions is very close to the <br />100 -year permitted flood plain elevation of 4874 feet. The model results show the <br />100 -year pre -mine water surface to be 4873.95. <br />