The stream buffer zone is a defined area along a stream or other watercourse that is protected from development, grading, construction, and other land-disturbing activities in order to preserve the stream’s natural benefits and reduce flood hazard risks along the stream corridor. Stream buffer zones are required to be delineated for all streams having a tributary area in excess of 40 acres. The delineation shall begin where the contributing drainage area meets 40 acres and continue downstream. Preservation of smaller streams having lesser contributing drainage area is encouraged.

The width of the stream buffer shall be determined per APWA Section 5600 criteria. Stream buffer widths are measured from the ordinary high-water mark (OHM) of the stream outward in each direction. Minimum stream buffer widths are defined in Table 5605-1 of the design criteria, which are summarized below:
 

¹ Measured from the OHM outward in each direction
² Preservation of streams with less than 40 acres of contributing drainage area is encouraged, but not required
 

Plats: Stream buffer zones shall be established around all preserved streams. The limits of stream buffer zones shall be formally designated on plats, easement, or other applicable documents as directed by the County. The following note should be included on preliminary and final plats: “No construction of disturbance of any type is allowed in the stream buffer zone except by permission of the County Engineer”.
 

Drainage calculations are required for the 100-year design storm and other applicable design storms to assess project impacts to ditches, streams, open channels, dams and other drainage facilities and ensure that new drainage facilities are properly designed. Hydrologic and hydraulic information from the FEMA effective watershed study should be utilized where available. Johnson County Street Construction and Storm Drainage Standards for Subdivisions and APWA Section 5600 criteria shall be followed to perform drainage calculations in areas where this information is not available. Project study limits should encompass the subject property and should extend upstream and downstream until water-surface elevations are no longer impacted.
 

Hydrologic and hydraulic information from the FEMA effective watershed study shall be utilized to perform design calculations for projects impacting the FEMA Special Flood Hazard Areas (SFHAs). Copies of the FEMA effective watershed study models can be requested through the Kansas Department of Agriculture - Division of Water Resources.

Requirements in Article 22 of the Johnson County Zoning and Subdivision Regulations shall be met for all projects within the SFHA. This includes, but is not limited to, the Zone A, Zone AE, Zone X (Future Conditions) floodplains and the floodway. A flood study and no-rise certification may be required depending on proposed impacts to the SFHA. Hydraulic analyses should be completed using HEC-RAS or other appropriate modeling software. 

Permitting: A floodplain development permit is required for any new development, re-development, or substantial improvements within the SFHA in accordance with Article 22 of the Johnson County Zoning & Subdivision Regulations. Additional state and federal permits may also be required depending on proposed impacts to the SFHA.

Plats: The limits of the effective FEMA floodplain zone(s) and floodway shall be formally designated on plats, easement, or other applicable documents as directed by the County. A note should be shown on the preliminary and final plats which references the appropriate FEMA FIRM panel(s) and Flood Insurance Study and provides information on which SFHAs are located within the platted area. In addition, the following note shall be included on the preliminary and final plats: ”Floodplains depicted on the plat are based on the best information available at the time the plat was prepared and recording. Building permit applications will be reviewed with respect to floodplain information available when each application is reviewed.”
 

Streams, roadways, dams, and other drainage infrastructure require field survey per Johnson County Street Construction and Storm Drainage Standards for Subdivisions and APWA Section 5600 criteria. Surveyed items may include, but are not limited to:
•    Channel cross sections
•    Profile along roadway centerlines
•    Profile along top of dam 
•    Crossroad structures including culverts and bridges
•    Spillway and outlet structures
•    Benchmarks