November 21, 2017

Division Four - Standards for Drainage - Chapter II. Definitions

Chapter II. Definitions

Sec. 402-1 Definitions:

402-1.01 AGENCY: refers to the Department of the County of Kern with jurisdiction.

402.1.02 ALLUVIAL FAN: is a landform originating at an apex and characterized by high-velocity flows; active processes of erosion, sediment transport, and deposition; and unpredictable flow paths.

402-1.03 APEX: means a point on an alluvial fan or similar landform below which the flow path of the major stream that formed the fan becomes unpredictable and alluvial fan flooding can occur.

402-1.04 CAPITAL STORM DESIGN DISCHARGE (CSDD): is that flow determined based upon a precipitation event having a one percent probability of being equaled or exceeded in any given year, commonly referred to as the 100 year storm.

402-1.05 CLOSED CONDUIT: is any system of underground drainage facilities, other than culverts. 195

402-1.06 COMPREHENSIVE DRAINAGE PLAN: refers to a storm water runoff mitigation plan for multi-phase developments. Such a plan need not be adopted by the County, but will be kept on file by the Director.

402-1.07 CONSTRUCTED CHANNEL: refers to the physical modification of natural channels or the construction of channels.

402-1.08 CONTROL FACILITY: are those hydraulic structures which mitigate the effects of surface runoff resulting from development, flow pattern modification, or flood flows.

402-1.09 CULVERT: is a hydraulically short conduit which conveys storm runoff flows through a roadway embankment or past some other type of flow obstruction.

402-1.10 DESIGN PONDING DEPTH: is the depth to which the design volume will pond in a storm water basin.

402-1.11 DETENTION BASIN: is a storm water facility designed to affect flood hydrograph peak attenuation.

402-1.12 EMBANKMENT AREA: is an area of compacted fill material.

402-1.13 ENCROACHMENT: refers to any change in land use that materially alters the lands flow conveyance potential.

402-1.14 FLOOD CONTROL PLAN: is a plan for the mitigation of flood flows originating from off-site watersheds, or resulting from on-site development.

402-1.15 FLOOD FLOW: shall be considered to be the CSDD for reference in these standards.

402-1.16 FLOW PATTERN: refers to any physical tracing resultant from the historic or existing runoff of water.

402-1.17 INTERMEDIATE STORM DESIGN DISCHARGE (ISDD): is that flow determined based upon a precipitation event having a ten percent probability of being equaled or exceeded in any given year, commonly referred to as the ten-year storm.

402-1.18 LEVEE: is an embankment whose primary purpose is to furnish drainage or flood protection from storm water runoff and which is, therefore, subject to water loading for periods of only a few days or weeks a year.

402-1.19 MASTER DRAINAGE PLAN: refers to a comprehensive drainage plan or flood control plan adopted by the County which includes adopted funding mechanisms.

402-1.20 NATURAL CHANNEL: is a flow pattern characterized by incised flow channelization with well defined banks and including the overbank flow areas.

402-1.21 NUISANCE FLOW: shall be considered as those waters originating from within, or adjacent to, the development not resulting from storm runoff.

402-1.22 ONE PERCENT RISK FLOW: is the flow on an alluvial fan based upon the joint probability of the flow distribution at the fan apex and the probability of occurring at the development site.

402-1.23 REASONABLE: in the context of this section refers to the balancing of the utility of the facilities or circumstances described against the gravity of the potential for harm.

402-1.24 RETENTION BASIN: is a terminal storm water facility for the storage of runoff. Commonly referred to as a sump.

402-1.25 RETARDATION BASIN: Synonymous with Detention Basin.

402-1.26 SLOPE EASEMENT: shall include the horizontal dimension from the top to toe of slope plus the setback requirements specified by the Grading Ordinance.

402-1.27 SOILS ENGINEER (GEOTECHNICAL ENGINEER): shall mean an engineer experienced and knowledgeable in the practice of soils engineering (geotechnical engineering).

402-1.28 SOILS ENGINEERING (GEOTECHNICAL ENGINEERING): shall mean the application of the principles of soil mechanics in the investigation, evaluation and design of civil works involving the use of earth materials and the inspection and/or testing of the construction thereof.

402-1.29 STRESS AREA: refers to those locations where the erosion potential is greater than a straight, uniform channel reach, and includes junctions, transitions, and curves.

402-1-30 WATERWAY: refers to any natural channel, artificial channel or closed conduit, which provides a course for drainage water to flow.

Sec. 402-2 Off-Site Capital Storm Design Discharge (CSDD) Mitigation

The CSDD flow determined from the off-site watershed shall consider the total area of the off-site watershed. The watershed development condition may be considered in its existing condition at the time of the proposed development if no control facilities mitigating surface runoff exist, and as undeveloped if adequate control facilities mitigating surface runoff exist.

The design of all structures within the development shall be protected to a minimum of one (1) foot above the water surface associated with the CSDD. The CSDD flow shall be received into the development without diversion onto adjacent property or causing more than one foot rise in pre-development water surface, and shall be discharged in a manner as similar as possible to the existing condition downstream of the development.

Sec. 402-3 Off-Site Intermediate Storm Design Discharge (ISDD) Mitigation

The ISDD flow shall be based upon the uncontrolled developed watershed proximate to the development when no defined flow pattern exists. When a flow pattern is defined, the ISDD flow determination shall include the total watershed contributing to the flow pattern. The off-site ISDD shall be mitigated in conjunction with requirements for on-site ISDD flows.

Sec. 402-4 Hydrologic Flow Determinations

The CSDD and ISDD flows shall be calculated in accordance with the current Kern County Hydrology Manual.


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