HomeMy WebLinkAboutInter-Dept Memo RE TPM20-0002 incomplete pending drainage Department of Public Works Dennis Schmidt, Director Radley Ott, Assistant Director Dan Newton, Assistant Director 7 County Center Drive T: 530.538.7681 Oroville, California 95965 F: 530.538.7171
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INTER-DEPARTMENTAL MEMO
PUBLIC WORKS DEPARTMENT
TO: TRISTAN WEEMS, PLANNING DIVISION
FROM: ERIC SCHROTH, LAND DEVELOPMENT DIVISION SUBJECT: INCOMPLETE APPLICATION – TPM20-0002
DATE: APRIL 16, 2020 The Public Works Department finds the application incomplete. Determining that a viable drainage system can be designed helps assure that CEQA requirements can be
met and that time and cost is not incurred for a tentative map that may not meet the requirements for recordation. To assure long-term operation and maintenance of storm drain facilities, the County recommends that the parcels be graded to drain into a storm drain leach trench
designed and constructed per standard 10.10 located within the dedicated road easement. The County is in the process of updating the improvement standards to clarify drainage requirements and disallow engineering designs that do not meet requirements for long-
term capture, conveyance, and disposal of storm water. Please consider modifying your preliminary drainage plan to a more conventional design. The preliminary plan proposes to construct a retention pond in a location not accessible for long-term maintenance by property owners who share an interest in it. These types
of excavations are frequently filled in by property owners. Therefore, compliance with County standards for creation of an easement to access and maintain the retention pond with motorized equipment is required. Show the proposed easement on the tentative map. Provide fencing to discourage property owners from modifying or filling the retention pond.
The preliminary plan proposes to convey and capture storm water through an open channel that grades at approximately 0.25%. The grade is not sufficient to convey storm water per County standards. The channel is located mostly upstream from lots to
Department of Public Works Dennis Schmidt, Director Radley Ott, Assistant Director Dan Newton, Assistant Director 7 County Center Drive T: 530.538.7681 Oroville, California 95965 F: 530.538.7171
buttecounty.net/publicworks
be created. Small conveyance ditches are frequently filled in by property owners. Submit calculations that demonstrate conveyance can meet the County’s standard for
minimum velocity of 2 feet per second. Comply with County standards for creation of an
easement to maintain the channel and access the retention pond with motorized vehicles. Show the proposed easement on the tentative map. Provide fencing to discourage property owners from modifying or filling the channel.
The preliminary plan proposes percolation, which is only allowed per County standard
10.10. Percolation not in compliance with 10.10 has a high documented rate of failure. Submit calculations that show accurate requirements for retention pond area and depth without considering percolation. Retention pond depth shall consider freeboard standards and minimum velocity standards of conveyance ditch.
The preliminary plan does not propose to capture or convey runoff from development of homes and hardscape. Submit a preliminary plan that demonstrates how storm water will be captured and/or conveyed from home site development such that it does not increase peak flow runoff.