2011-12-16_REVISION - M1977572 ‎(71)‎

• Permit No: M1977572
• IBM Index Class Name: REVISION
• Doc Date: 12/16/2011
• Doc Name: Submittal
• From: VALCO
• To: DRMS
• Type & Sequence: TR2
• Media Type: D
• Archive: No

IV. PROPOSED IMPROVEMENTS
A flood mitigation plan was developed for the subject property including site grading and
erosion protection. Proposed improvement to the Valco property are intended to mitigate impacts to
the 100 -year floodplain, minimize erosion potential at the Highway 50 Bridge, and meet Colorado
Division of Reclamation Mining and Safety requirements for reclamation.
4.1 Design Criteria
Three sets of design criteria were established prior to development of the proposed site grading
and erosion protection including:
1. 100 -Year Floodplain Requirements: Hydraulic analysis of proposed site grading will show
lowering of the existing 100 -year water surface elevations down to (or lower than) the corrected
effective (FEMA regulatory) condition.
2. Erosion Protection: Minimize the gravel pit induced erosion potential at the US Highway 50
Bridge.
3. Colorado Division of Reclamation Mining and Safety Regulations: Proposed grading plan will
meet requirements stated in Section 3.1.5 (specifically Sub - Section 7 regarding safe slopes) of
the "Mineral Rules and Regulations of the Colorado Mined Land Reclamation Board for the
Extraction of Construction Materials," dated October 1995 (amended August 2006).
4. Exposed Water Surface: The proposed grading plan will not increase the overall exposed water
surface area on the subject property and where possible the grading plan will attempt to lessen
the overall exposed water surface area.
4.2 Grading Plan
A proposed grading plan including 1 -foot topography is provided in Appendix C. All elevations
reference NAVD88. The proposed site grading includes the following modifications to the existing site
topography as well as a brief explanation of their benefits.
• An inlet section along Berm A having a crest elevation no higher than 3608, a bottom width of
approximately 300 feet, and 3:1 side slopes. Establishment of an inlet and lowering of Berm A
will help meet floodplain requirements and safely convey water into the overbank area
minimizing erosion potential.
• Lowering of the ground along Berm B to an elevation of 3606 or less. This modification provides
proper conveyance of flow during the 100 -year event in order to meet floodplain requirements.
• Pit #2 will be filled in to an elevation no higher than 3607 in order to minimize the exposed open
water surface area.
COVALCOO1_Phase 11 Report_082211.docx
4.1 ANdERSON CONSULTING ENGINEERS, INC.