SUBJECT: The U.S. Army Corps of Engineers, Sacramento District, (Corps) is evaluating a permit application to construct the Cottonwood Cove Flood Mitigation Structure project, which would result in permanent impacts to approximately 2,048 linear feet/2.02 acres and temporary impacts to 15,756 linear feet/14.12 acres of ephemeral waters of the United States that flow to Lake Mohave. This notice is to inform interested parties of the proposed activity and to solicit comments.
AUTHORITY: This application is being evaluated under Section 404 of the Clean Water Act for the discharge of dredged or fill material in waters of the United States.
APPLICANT: National Park Service, Lake Mead NRA
Attn: Ms. Margaret Goodro
601 Nevada Way
Boulder City, Nevada 89005
LOCATION: The approximately 0.5-mile long flood mitigation structure is located one mile north of the Cottonwood Cove developed area on Ranger Wash and unnamed tributaries to Lake Mohave, within the boundaries of the Lake Mead National Recreational Area, Assessor’s Parcel Numbers 24500002004 and 24500002005, Latitude 35.4909°, Longitude -114.7067°, Clark County, Nevada, and can be seen on the Spirit Mountain NW USGS Topographic Quadrangle.
PROJECT DESCRIPTION: The applicant is proposing to construct a flood mitigation project. Based on the available information, the overall project purpose is to improve safety of visitors and NPS employees in Cottonwood Cove by reducing the risks of flooding from a 500-year storm event. The applicant believes there is a need for additional flood control measures to divert flash flood flows away from the developed Cottonwood Cove area because it is a high hazard area for flash floods. Existing flood control measures there (consisting of small diversion dikes and ditches) do not protect Cottonwood Cove from a 500-year storm event, the size of flood event that Nation Park Service (NPS) has determined the area requires protection from. This project therefore is being implemented to (1) protect the health and welfare of the public and NPS employees; (2) preserve natural and cultural resources; (3) and improve operational efficiency, reliability, and sustainability. The 0.5-mile-long flood mitigation structure would consist of four components: the south berm, the south channel, the north berm, and the north channel that, once constructed, would divert flows from Ranger Wash into the North Wash before the flows reached the Cottonwood Cove developed area. In the attached figures, the four components are represented using solid colors and associated sloping areas are represented using hatch lines (Figures 4 and 5). Construction of these components would permanently impact 2,048 linear feet/2.02 acres of ephemeral streams with placement of 3,046 cubic yards (CY) of native soil and 206 CY of soil cement. Construction of the project would result in the creation of 4,180 linear feet/2.95 acres of ephemeral drainage being constructed to redirect the flows in and through the flood control structure. Temporary impacts from the access road, construction areas, staging areas and borrow areas would result in temporary impacts to 15,756 linear feet/14.12 acres of ephemeral streams resulting from the placement of 22,272 CY of native soil and 3,887 CY of soil cement. The temporary impact areas are proposed to be restored to pre-construction contours following the completion of construction. The attached drawings provide additional project details.
Environmental Setting. There are approximately 25,431 linear feet/23.6 acres of ephemeral streams within the project area. The site is characterized by highly braided, episodic, ephemeral stream system that is subject to flash flooding and conveys periodic flows from convective storm events from Black Mountain, approximately 3.5 miles downstream into Lake Mohave.
Ranger Wash (Feature B, Figures 6 and 7) and unnamed tributaries flowing to Ranger Wash (Features C and D, Figures 6 and 8) would have their flows diverted as a result of the proposed project. These flows would be diverted into the North Wash (Feature F, Figures 8 and 9). Construction of the flood control structures would result in impacts to all of the above mentioned features and to Features A, G, and E (Figures 6 and 8).
Alternatives. The applicant has provided information concerning project alternatives. Alternatives considered in addition to the proposed alternative included the no action alternative, differing levels of flood protection, and other engineering solutions and footprints. Information regarding alternatives for differing levels of flood protection are available from the National Park Service at the following websites: Cottonwood Cove and Katherine Landing Final Development Concept Plans/Environmental Impact Statement, https://parkplanning.nps.gov/document.cfm?parkID=317&projectID=23037&documentID=6237 3 and the corresponding Record of Decision is located here: https://parkplanning.nps.gov/document.cfm?parkID=317&projectID=23037&documentID=6448 5. Further, information regarding the design selection is available from the National Park Service Value Analysis Files located here: https://www.nps.gov/dscw/design_vafiles.htm. Other alternatives may develop during the review process for this permit application. All reasonable project alternatives, in particular those which may be less damaging to the aquatic environment, will be considered.
Mitigation. The Corps requires that applicants consider and use all reasonable and practical measures to avoid and minimize impacts to aquatic resources. If the applicant is unable to avoid all impacts to waters of the U.S., the Corps may require compensatory mitigation. The applicant has not proposed compensatory mitigation for the proposed impacts because the project would result in a net gain of 2,132 linear feet/0.93 acres of ephemeral streams in the areas identified as Areas A, B, C, D, and E on the attached drawings (Figure 5).
OTHER GOVERNMENTAL AUTHORIZATIONS: Water quality certification or a waiver, as required under Section 401 of the Clean Water Act from the Nevada Division of Environmental Protection is required for this project. The applicant has indicated they have applied for certification.
HISTORIC PROPERTIES: The National Park Service is the lead federal agency and is responsible for consultation with the State Historic Preservation Officer under Section 106 of the National Historic Preservation Act, as appropriate. In a letter dated February 21, 2020 the National Park Service received concurrence from the State Historic Preservation Office on their determination that the project would have no adverse effect to historic properties.
ENDANGERED SPECIES: The proposed activity may affect Federally-listed endangered or threatened species or their critical habitat. The National Park Service has initiated consultation with the U.S. Fish and Wildlife Service (the Service), pursuant to Section 7 of the Endangered Species Act and the Service has concurred with the finding that the project as proposed would not likely jeopardize the continued existence of the threatened Mojave desert tortoise (Gopherus agasizii).
The above determinations are based on information provided by the applicant and our preliminary review.
EVALUATION FACTORS: The decision whether to issue a permit will be based on an evaluation of the probable impacts, including cumulative impacts, of the described activity on the public interest. That decision will reflect the national concern for both protection and utilization of important resources. The benefit, which reasonably may be expected to accrue from the described activity, must be balanced against its reasonably foreseeable detriments. All factors which may be relevant to the described activity will be considered, including the cumulative effects thereof; among those are conservation, economics, aesthetics, general environmental concerns, wetlands, historic properties, fish and wildlife values, flood hazards, floodplain values, land use, navigation, shoreline erosion and accretion, recreation, water supply and conservation, water quality, energy needs, safety, food and fiber production, mineral needs, consideration of property ownership and, in general, the needs and welfare of the people. The activity's impact on the public interest will include application of the Section 404(b)(1) guidelines promulgated by the Administrator, Environmental Protection Agency (40 CFR Part 230).
The Corps is soliciting comments from the public, Federal, State, and local agencies and officials, Indian tribes, and other interested parties in order to consider and evaluate the impacts of this proposed activity. Any comments received will be considered by the Corps to determine whether to issue, modify, condition, or deny a permit for this proposal. To make this decision, comments are used to assess impacts on endangered species, historic properties, water quality, general environmental effects, and other public interest factors listed above. Comments are used in the preparation of an Environmental Assessment and/or an Environmental Impact Statement pursuant to the National Environmental Policy Act. Comments are also used to determine the need for a public hearing and to determine the overall public interest of the proposed activity.
SUBMITTING COMMENTS: Written comments, referencing Public Notice SPK-2019-00870 must be submitted to the office listed below on or before April 23, 2020.
Jennifer Thomason, Project Manager
US Army Corps of Engineers, Sacramento District
Reno Regulatory Field Office
300 Booth Street, Room 3050
Reno, Nevada 89509
The Corps is particularly interested in receiving comments related to the proposal's probable impacts on the affected aquatic environment and the secondary and cumulative effects. Anyone may request, in writing, that a public hearing be held to consider this application. Requests shall specifically state, with particularity, the reason(s) for holding a public hearing. If the Corps determines that the information received in response to this notice is inadequate for thorough evaluation, a public hearing may be warranted. If a public hearing is warranted, interested parties will be notified of the time, date, and location. Please note that all comment letters received are subject to release to the public through the Freedom of Information Act. If you have questions or need additional information please contact the applicant or the Corps' project manager Jennifer Thomason, by phone at (775) 784-5304, or by email at Jennifer.C.Thomason@usace.army.mil.
Attachments: 9 drawings