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Two Rivers Gravel Pit Mine <br /> Riverside Berm Failure Analysis <br /> and Flood Control Mitigation Plan <br /> 7ech"olooicess January 22,2020 <br /> farmland from frequent flooding. It is estimated (engineering judgment)that the earthen berm <br /> will protect the site from a 10-yr flood, but that varies throughout. Design and construction <br /> information is not readily available. Note that the term "earthen berm" is referred to within this <br /> report for Two Rivers. However, embankments along rivers are technically "levees" but those at <br /> the site are not FEMA certified; thus, FEMA doesn't recognize them for flood insurance studies. <br /> WELD COUNTY <br /> Two Rivers 00 . <br /> I F a <br /> i <br /> - <br /> \ Legend <br /> Fbadplan 500 Year <br /> 0.11 <br /> b Rad-o Fbadplan 100 Year Zo A <br /> 1� ��/ c To. �-..� - , \ Fk dpls n 100 Vear Mod— <br /> ` G. _c � '—�� �'_�\���- FbadPlan 100 Year Zone AE <br /> I r ^� Vear Zone AIL <br /> _{i}�'\•�� ake r��l _� Floodway Fbndplan 10ovearZo—Ac <br /> % .)'( S / •�--,F— - .: ,' a\N �„Y.arm - — Highway <br /> `,' �a•a r Two Rivers 3LE <br /> ,.. _ LEI`—L Q County Boundary <br /> UR• Big° _ ,S'1 /— _ rH <br /> r WCR•46 <br /> U U <br /> � 3 � <br /> �pU //0 ! µrimy` — a <br /> 3 &� <br /> WCR.nr. WCR-46 - WCW46 i <br /> 3 1:56,603 O <br /> Notes <br /> eet ml::p.pl:n:erya,erared srdtic o�urnom al:iremef«appl:y:ire aa eror weld mprn erppem aprcal <br /> reference only.naG layers dia[appear m Mls map mayor may not be aecurale, <br /> _ _ux ry_p re Bent,or rnMrvnse reliable. <br /> e on:aymo,a n <br /> Figure 3 <br /> Two Rivers FEMA 100-yr floodplain <br /> III. STUDY METHODOLOGY <br /> Two Rivers site is unique and complex because it is located between the Big Thompson and <br /> South Platte Rivers just upstream from their confluence. The site is capable of experiencing <br /> flooding-from both rivers at the same time, so when all three pits are at maximum extraction <br /> flood waters can enter them from anywhere around the perimeters with potential for head <br /> cutting/erosion. <br /> Head cutting on a pit's inside perimeters is not a concern because the furthest the head cut can <br /> extend would essentially be to an adjacent pit within the site. However, head cutting on a pit's <br /> riverside berm has the potential to erode through the riverside berm between the pit and river <br /> which is the focus of this study. <br /> pg.9 <br />