Chapter 27A



27A.1    Purposes and intent.

27A.2    Definitions.


27A.3    Applicability.

27A.4    Exemptions.

27A.5    Building and site requirements.

27A.6    Required plans for modifications.


27A.1 Purposes and intent.

The purpose and intent of this article is:

(a) To protect the City of Gilroy’s water resources and to provide a reliable supply of healthy and clean water.

(b) To reduce the potential for flood damage.

(c) To protect and when appropriate to enhance or restore the natural resources of streams and watersheds. (2007-11, § 4-16-07)

27A.2 Definitions.

This section defines terms that have meanings specific to the interpretation of this chapter.

“Development” means the placement or erection of any solid material or structure; grading, removing, dredging, mining, or extraction of any materials; construction, reconstruction, demolition, or alteration of the size of any structure, including any facility of any private, public, or municipal utility; and the removal or installation of vegetation.

“Guidelines and standards” means a set of model guidelines, standards, procedures, and recommendations developed for land use activities near streams, for streamside properties, and for the protection of streams and streamside resources.

“Modification” means any alteration to properties in the streamside review area, including but not limited to the activities defined under development.

“Pollution” means impairment of water quality to a degree which adversely and unreasonably affects a beneficial use of the water.

“Riparian vegetation” means vegetation growing on or near the banks of a stream or other body of water on soils that exhibit some wetness characteristics during some portion of the growing season.

“Storm water” means surface runoff directly resulting from precipitation without being subject to intermediate natural processes, such as infiltration into the soil.

“Stream” means a body of water that flows at least periodically or intermittently through a bed or channel having banks. This water may include watercourses having a surface or subsurface flow that supports or has supported riparian vegetation, fish or other aquatic life.

“Streamside review area” means all properties abutting or in proximity to a stream, including all properties located within fifty (50) feet from the top of bank.

“Structure” means anything made or constructed and having its foundation or support upon or within the ground.

“Top of bank” means a stream boundary where a majority of normal discharges and channel forming activities takes place. The top of bank boundary contains the active channel, active floodplain, and their associated banks. Top of bank streams with levees will be delineated on the inner edge of the levee. Where there are no distinguishable features to locate top of bank, the City Engineer or designee will make a determination and document as appropriate. In the absence of this determination, the 100-year water surface will be used.

“Two to one (2:1) slope stability protection area” means a distance measured using a hypothetical two (2) horizontal to one (1) vertical line projected from the toe of bank to a point where it intersects the adjacent ground. (2007-11, § 4-16-07)


27A.3 Applicability.

The following regulations shall apply to all properties within a streamside review area, and shall be subject to all of the general provisions of this chapter. All development subject to this chapter shall also be subject to review for applicability of the “Guidelines and Standards for Land Use Near Streams” ratified by the Water Resource Protection Collaborative. (2007-11, § 4-16-07)

27A.4 Exemptions.

The following land use activities are exempt from this chapter. However, these activities must not be located in a stream channel:

(a) Remodel of existing single family residences on parcels ten thousand (10,000) square feet or less.

(b) Less than three (3) cubic yards of earthwork.

(c) Interior building construction and alterations.

(d) Erection of storage buildings not greater than one hundred twenty (120) square feet. Accessory structures should be sited in a manner that causes the least disruption to the stream/streamside resources.

(e) Replacement of sewer or water laterals.

(f) Re-roofing.

(g) Wood fences six (6) feet in height or less that are set back from the top of bank.

(h) Exterior decks thirty (30) inches or less in height above grade that do not overhang or extend beyond the creek bank.

(i) Any modification to the site that occurs fifty (50) feet or more from the top of bank or edge of riparian corridor, whichever is greater. (2007-11, § 4-16-07)

27A.5 Building and site requirements.

All development subject to this chapter shall comply with the following requirements and also be subject to review for applicability of the “Guidelines and Standards for Land Use Near Streams”.

(a) Riparian Corridor Protection.

(1) Removal of native vegetation is not permitted. Non-native species are not allowed to be planted between top of banks. Invasive species are not allowed within one hundred fifty (150) feet of top of bank. All new landscaping must comply with the adopted City of Gilroy’s Consolidated Landscape Policy.

(2) Avoid bright colors and glossy or glare producing building finishes on structures facing the stream or riparian areas. Avoid night time lighting, direct lighting away from and maximize the distance of lighting from the riparian corridor.

(b) Bank Stability/Slope Stability Protection Area.

(1) Placement of new roads, parking lots, pools and structures subject to the Uniform Building Code shall be placed outside a slope stability protection area in a location and manner that avoids or minimizes impacts to streams, streamside natural resources, flood protection and local drainage infrastructure and the proposed structure.

(2) For all new development and major redevelopment, the slope stability protection area is the greater of:

a. A two (2) to one (1) slope stability protection measured using a hypothetical two (2) horizontal to one (1) vertical line projected from the toe of bank to a point where it intersects the adjacent ground. The protection area should allow for construction access and access around the structure. For banks of large streams, or for streams that are deeply incised or have highly erodible banks, the city engineer may increase the protection area in order to protect water quality, the riparian corridor, and other resources.

b. Twenty (20) feet from top of bank or property line.

c. If a non-exempt structure is proposed within the slope stability protection area, the applicant shall conduct a study of on-site geotechnical and slope stability conditions:

The purpose of the study is to determine:

1. Whether the location of the proposed structure may threaten bank stability; and

2. Whether the bank is in an unstable or potentially unstable condition that may threaten structures and/or potentially cause a health and safety hazard.

The study needs to include a geotechnical analysis of soil conditions, a slope stability analysis that considers static conditions and the action of the stream on the bank. The study must:

1. Demonstrate that development would not require introduction of hardscape in order to maintain a stable slope; and

2. Show how maintenance or repair of the stream could be provided should it become necessary.

(c) Encroachments between the Top of Bank.

(1) Privately owned decks, pathways, or buildings may not overhang or encroach beyond or within the top of bank.

(2) Structures must not reduce the active channel or active floodplains’ conveyance area or redirect flow to the detriment of another bank and must be designed to convey 100-year design flow.

(3) Bridge construction should be clear span construction. When not feasible, bridge piers may be allowed, subject to determination by the City Engineer. Pier footings and pile caps should be designed based on channel scour to prevent erosion and be a minimum of three (3) feet below active channel invert.

(4) Encroachments in active channels and active floodplains must provide for fish passage, if applicable, and respect aquatic life.

(d) Erosion Prevention and Repair.

(1) Construction on slopes greater than five (5) percent, must implement erosion and sediment control measures.

(2) Remediate source of on-site erosion (i.e. roof downspouts or overbank drainage). Design of erosion protection must utilize the softest possible method appropriate for the stream characteristics. Include revegetative measures in any new development project, even if not used in erosion repair. All erosion repair projects must include an evaluation for the potential impacts on both downstream and upstream banks.

(3) Bare earthen slopes resulting from work must be treated, as necessary, to minimize erosion and prevent sediment from entering streams and other aquatic habitats.

(e) Grading.

(1) Grading adjacent to a stream must provide for buffer areas and vegetated swales between the stream and graded areas.

(2) All grading must address site drainage.

(f) Outfalls, Pump Stations and Site Drainage.

(1) Direct site drainage through vegetated areas or stilling basins prior to discharge or collection in storm drain system. No concentrated overbank drainage is allowed (e.g. roof overhangs or downspouts). If overbank drainage will occur, use vegetative buffer strips or direct drainage to landscaped areas.

(2) The use of outfalls should be minimized or avoided wherever possible.

(3) Limit pump discharges to a stream to the extent feasible during peak flows to minimize potential impacts from flooding.

(g) Channelization.

(1) Streams must not be buried or put into culverts.

(2) Any open channel modification must consider the stream dynamics and induced flooding. Stream conveyance area must be designed for 100-year design flow with freeboard. Any modifications must include restoration of natural stream processes and avoid or mitigate where avoidance is not possible any impacts to habitat areas.

(h) Utility Encroachments.

(1) Utility pipes or conduits must go under the stream or be in or attached to the downstream face of a bridge and must go under any levees.

(i) Trail Construction.

(1) Trails must be located so as to avoid impacts to the stream riparian areas. Paved multi-use trails should be placed so as to maximize the distance from stream and riparian areas.

(j) Protection of Water Quality.

(1) Any non-storm water discharges must not pollute surface water and shall be subject to approval and permit from the regional water quality control board.

(k) Groundwater Protection.

(1) A groundwater resource assessment is required when there is a potential for significant groundwater supply or groundwater quality impacts.

(l) Flood Protection.

(1) New development must not increase flooding one-tenth (0.1) foot increase in water surface or reduce freeboard below minimum required. A hydraulic analysis prepared by a licensed civil engineer demonstrating that any flood impact will not be created is required.

(2) Buildings shall be set back from the toe of any levee by a minimum of twenty (20) feet. (2007-11, § 4-16-07)

27A.6 Required plans for modifications.

All properties located within the streamside review area making any non-exempt modifications (see section 27A.4, exemptions) to their property, must submit plans drawn to scale and of sufficient clarity to indicate the nature and extent of the work, bank stabilization and revegetation efforts proposed that includes the following information:

(a) Name and address of owner;

(b) Name and address of applicant (if different from owner);

(c) Name, address, professional status, license number, and phone number of the person who prepared the plan;

(d) Location and assessor’s parcel number of the proposed site;

(e) North arrow, scale, and the name and location of the nearest public roads, streams, watercourses within 100 ft. of proposed activity;

(f) Existing contours of the site, as well as finished contours to be achieved by grading. Contours shall be sufficiently detailed to define the topography over the entire site (generally at two-foot intervals);

(g) Detailed plans of all bank stabilization and erosion control measures

(h) Delineation of areas to be cleared during development activities;

(i) Location of top of bank or edge of riparian corridor with a fifty-foot buffer area from the edge;

(j) Restoration vegetation proposed for all surfaces to be exposed during development activities, including any dredged, filled or graded areas;

(k) The location and extent of open space buffers and method implementation;

(l) Any use restrictions and method of implementation.

Plans shall be reviewed in conjunction with any and all other applicable city permits required for the proposed modification and/or development. (2007-11, § 4-16-07)