Chapter 16.64 — DRAINAGE

All portions of the subdivision shall be protected from flood hazard, inundation, sheet overflow and ponding of stormwaters, springs and all other surface waters. All finished floors shall be above the water surface of a one-hundred (100) year frequency storm runoff.

(CCCC§ 914-2.002)

The design of all improvements within the subdivision shall be such that all surface waters occurring within the subdivision, as well as all surface waters flowing onto and/or through the subdivision, shall be conveyed through the subdivision without damage to any improvement, building site, or dwelling which may be constructed within the subdivision. Storm drainage facilities within the subdivision shall be

designed to adequately convey the stormwater runoff from the ultimate development of the drainage basin or watershed.

(CCCC§ 914-2.004)

A.

Surface waters flowing from the subdivision in any form or manner shall be conveyed without damage to any improvement, building or dwelling to a natural watercourse having a definable bed and banks, or to an existing adequate storm drainage facility. Storm drainage facilities to be constructed outside of the subdivision shall be designed to adequately convey the stormwater runoff from the ultimate development of the drainage basins or watershed lying within and above the subdivision.

B.

Wherever surface waters must be conveyed beyond the boundaries of the subdivision in order to discharge into a natural watercourse or to an existing adequate storm drainage facility, the subdivider shall comply with either subsections C, D or E of this section, prior to filing of the final map or parcel map.

C.

The subdivider shall deposit with the Public Works Department a copy of a duly recorded drainage release from the adjacent property owners in a form and content acceptable to the City Council, accepting the flow of surface waters from the subdivision onto and over that property, or the detention and ponding of surface waters upon that property, without liability by the city for damages occurring therefrom. Such releases shall be obtained from all property owners between the boundaries of the subdivision and the point at which the surface waters will enter a natural watercourse having definable bed and banks or an existing adequate storm drainage facility.

D.

The subdivider shall deposit with the Public Works Department a copy of a duly recorded grant of a drainage easement to the city from the property owner(s). Such a document shall be obtained from all property owners between the boundaries of the subdivision and the point at which the surface waters will be discharged into a natural watercourse or an existing adequate storm drainage facility, or the area upon which surface waters will be detained and ponded.

E.

The subdivider shall present written evidence which proves to the satisfaction of the Public Works Department that it is not feasible to obtain by negotiation from the property owner(s) either a drainage release or a grant of drainage easement. The Public Works Department may then authorize the subdivider to institute condemnation proceedings to obtain the easement.

F.

Whenever it shall appear to the subdivider that those heretofore mentioned matters relating to the acquisition of drainage releases and easements, and/or the institution of condemnation proceedings, may be more expeditiously administered by the city, the subdivider may request that the City Council direct the Public Works Department to assume the responsibility for proceeding with these matters. The City Council, upon such terms and conditions as they specify, may authorize the department to act on behalf of the subdivider in complying with subsection B of this section.

(CCCC§ 914-2.006)

16.64.040 - Surface water flowing to subdivision.

Whenever surface waters flowing to or onto the subdivision in any form or manner will be detained or ponded on adjacent property(s) as the result to improvements constructed by the subdivider, the subdivider shall comply with Section 16.64.030 prior to the filing of the final map or parcel map.

(CCCC§ 914-2.008)

16.64.050 - Stormwater disposal restrictions.

Stormwaters flowing from the subdivision in any form or manner shall not be permitted to flow into any water conveyance facility of the Contra Costa Canal, nor into any other water conveyance or impounding facility for domestic water consumption.

(CCCC§ 914-2.010)

16.64.060 - Runoff quantity determination.

Runoff quantities shall be determined by methods consistent with current engineering practices using basic data supplied by the Public Works Department for the frequency of the average recurrence interval stipulated in Section 16.64.070.

(CCCC§ 914-2.012)

16.64.070 - Drainage facilities—Minimum capacities.

Drainage facilities directly affecting the subdivision shall have the following minimum capacities:

A.

Major drainage channels and conduits shall have sufficient capacity to contain a fifty (50) year frequency of average recurrence interval runoff;

B.

Secondary drainage channels and conduits shall have sufficient capacity to contain a twenty-five (25) year frequency of average recurrence interval runoff;

C.

Minor drainage facilities, channels and conduits shall have sufficient capacity to contain a ten-year frequency of average recurrence interval runoff.

(CCCC§ 914-2.014)

Waters within street areas shall be placed in closed conduits when the maximum depth of computed flow exceeds the capacity of the gutter or creates a traffic hazard or endangers property. Stormwater in natural or artificial drainage channels shall be placed in closed conduits or concrete lined channels where the quantity does not exceed eighty (80) cubic feet per second except that the advisory agency may recommend that an existing natural watercourse endowed with significant natural beauty in the form of trees, shrubs or scenic attraction may be utilized for an open drainage facility with such drainage improvements as may be designated by the Public Works Department. Such areas shall either be dedicated as easements or designated on the final map or parcel map as drainage reserves upon and within which no improvements or structures of any nature shall be constructed without the written consent of the Public Works Department.

(CCCC§ 914-2.016)

Design of drainage channels, conduit and appurtenances shall conform with design standards of the Public Works Department.

(CCCC§ 914-2.018)

16.64.100 - Culverts.

A.

Under-Driveway Culverts. Culverts under driveway entrances for roadside ditches shall be adequate to carry the design flow, but shall not be less than twelve (12) inches inside diameter.

B.

Street-Crossing Culverts. Culverts crossing the street shall be of a size adequate to carry the design flow, but shall not be smaller than fifteen (15) inches inside diameter for concrete or eighteen (18) inches inside diameter for corrugated metal pipe or aluminum pipe.

C.

Culverts Outside the Roadway. Culverts for use outside the roadway may be of any approved type and strength to meet field conditions.

(CCCC§§ 914-4.202 — 914-4.206)

16.64.110 - Roadside ditches.

A.

Discharge to Roadside Ditches. No concentrated flow of stormwaters from a subdivision shall be discharged into a roadside ditch.

B.

Roadside Ditch Sections. Roadside ditch sections shall be subject to the approval of the Public Works Department as to shape, size, gradient, lining, and location within the road right-of-way, and shall have the required hydraulic capacity.

C.

Purpose of Roadside Ditches. Roadside ditches and gutters shall be provided to carry the drainage from the road and tributary lands without damage to the roadbed or abutting property.

D.

Roadside Ditch Gradients. The maximum gradient for earth roadside ditches shall not exceed four percent, nor be less than one percent. The minimum gradient for lined roadside ditches shall not be less than one percent.

(CCCC§§ 914-4.402 — 914-4.408)

All corrugated steel and aluminum pipe intended for use within the roadway shall be of the gauge recommended by the manufacturer and approved by the Public Works Department for the cover and service conditions required. Corrugated steel and aluminum pipe shall be bituminous coated where required by the Public Works Department. Additional protective coating or paving of metal pipes may be required for severe service conditions. The gauge of pipe proposed at each location shall be noted on the improvement plans.

(CCCC§ 914-4.602)

Storm drain inlets shall be of a design approved by the Public Works Department. Water shall be directed into the storm drain inlet without a reversal of direction of the flow of the water.

(CCCC§ 914-4.604)

Drainage structures shall allow for tidal action and flood stage where applicable. The hydraulic pressure elevation in any storm drainage system shall be at least one and twenty-five-hundredths feet below the top of any inlet grate or manhole.

(CCCC§ 914-4.606)

16.64.150 - Earth channels.

A.

Maximum Design Velocities. Maximum design velocities for natural or artificial earth channels shall be those specified by a soil engineer in the preliminary soil report.

B.

Minimum Velocities. Minimum velocities at design capacity for earth channels shall be three feet per second.

C.

Side Slopes. Side slopes for improved earth channels shall be those specified by a soil engineer, but in no instance shall side slopes be steeper than one and one-half horizontal to one vertical.

(CCCC§§ 914-6.002 — 914-6.006)

16.64.160 - Lined channels—Side slopes.

Side slopes for lined channels shall be those specified by a soil engineer.

(CCCC§ 914-6.008)

16.64.170 - Closed conduits—Minimum flow line.

Minimum flow line gradients for closed conduits shall be not less than three one-thousandths foot per foot.

(CCCC§ 914-6.010)

16.64.180 - Closed conduits or lined channels—Outlet velocity.

Where the outlet velocity from a closed conduit or line channel exceeds the maximum allowable velocity for the earth channels receiving the flow, suitable protective works such as riprap or a stilling basin shall be provided.

(CCCC§ 914-6.012)

16.64.190 - Clearance of natural channels.

The subdivider shall, within the boundaries of the subdivision, selectively clear all natural channels and watercourses of all structures, trees, brush, and debris which would interfere with or obstruct the flow of stormwaters.

(CCCC§ 914-6.014)

16.64.200 - Levees.

A.

Compliance Requirements. Adequate levees shall be provided in compliance with Section 16.64.010.

B.

Toe and Slope Requirements. For levees used in combination with open channels and waterways, the toe of the levee on the water side shall be placed at least two feet back from the top of the bank of channel or waterway. Levee slopes shall not be steeper than two horizontal to one vertical.

C.

Top Width. Top width of outer or circumferential levees constructed for the protection of reclaimed lands shall be not less than eighteen (18) feet.

D.

Earth Embankments. Earth embankment necessary for protection of any portion of the subdivision from surface waters and not adjacent to open channels or waterways shall have minimum top width of five feet. Embankment slopes shall be the same as for levees.

E.

Degree of Protection. The degree of protection for which levees shall be designed shall be as follows:

1.

For watercourses and channels, levees shall provide the degree of protection as specified in Section 16.64.060;

2.

For those areas to be protected from water of San Francisco Bay and San Pablo Bay from the southerly and westerly boundaries of Contra Costa County to the state highway bridge at Carquinez Strait, levees shall provide protection from tides and from waves created by wind action. Tops of curbs shall be not lower than elevation 7.5 U.S.G.S. datum;

3.

For those areas to be protected from the waters of Carquinez Strait and Suisun Bay from the state highway bridge at Carquinez Strait to Simmons Point on Chipps Island, levees shall provide protection from tides, flood flows in the Sacramento and San Joaquin Rivers, and waves created by wind action. The basis for flood protection shall be the U.S. Army Corps of Engineers' standard project flood, approximately equivalent to a recurrence interval of two hundred years. Tops of curbs shall be not lower than elevation 8.5 U.S.G.S. datum;

4.

For those areas within the delta area from Simmons Point on Chipps Island to the easterly boundaries of Contra Costa County, levees shall provide protection from tides, flood flows in the Sacramento and San Joaquin rivers and all waterways tributary thereto, and waves created by wind action. The basis for flood protection shall be the U.S. Army Corps of Engineers' standard project flood, approximately equivalent to a

recurrence interval of two hundred (200) years. Tops of curbs shall be not lower than elevation 9.5 U.S.G.S. datum.

F.

Approval of Design and Construction. Approval of design and construction of all levees within those areas described in subsection (E)(2), (3) and (4) of this section, shall be obtained from the U.S. Army Corps of Engineers, California State Reclamation Board, San Francisco Bay Conservation and Development Commission, and any active operating local reclamation district within whose boundaries levees are to be constructed.

G.

Control and Maintenance. The jurisdiction for the control and maintenance of all required levees shall be as determined by the city, except as to areas where reclamation districts or districts with similar powers have such responsibilities, in which case the district having that responsibility shall present assurances satisfactory to the city that they have the necessary means and will perform the continued necessary maintenance of those levees protecting the subdivision.

(CCCC§§ 914-8.002 — 914-8.014)

Minimum widths of drainage easements for closed conduit shall be equal to the outside diameter or width of the conduit plus three feet on each side, but in no location less than ten feet. Easement widths shall be rounded up to the nearest foot. Drainage easements shall not be divided longitudinally by lot lines.

(CCCC§ 914-10.202)

A.

Improved Channels — Minimum Width of Easements. The width of drainage easements for excavated earth channels and channels greater than three feet in width that are lined with concrete or other materials, shall contain the full outside top width of channel, including lining and the required adjacent access easements. For lined channels having a top width less than three feet, the minimum width of drainage easement shall be ten feet.

B.

Improved Channels — Access Easements.

1.

For excavated earth channels within the subdivision, access and maintenance shall be provided along the banks as follows:

Channel Top Access Easements

2.

For lines channels within the subdivision, access and maintenance easement shall be provided along the banks as follows:

3.

Access and maintenance easement shall be graded in such a manner so as to be usable by vehicular maintenance equipment, but they need not be surfaced. Minimum radius of centerline of such easements shall be forty (40) feet. All such easements along channels shall be provided with ingress from a public way and be usable by vehicular maintenance equipment. The minimum width of the ingress shall be twelve (12) feet. Where trees in place on and adjacent to channel banks are to remain, adequate additional vehicular easement width shall be offered for dedication.

C.

Unimproved Channels — Structure Setback.

1.

"Structure setback line" means the line separating the structure setback area from the remainder of the lot. For unimproved earth channels within the subdivision, a structure setback line shall be shown on the final or parcel map as follows: the thread of the channel shall be shown as accurately as possible, and a dashed line shall indicate the appropriate setback with a note describing the formula used, selected from those set forth herein. The development rights for that portion of the lot on the creek side of the setback line shall be offered for dedication to Contra Costa County by separate instrument.

2.

Channels less than twenty (20) feet deep: the structure setback line for unimproved channels with existing side slopes steeper than 2.5:1 (2.5 feet horizontal to one foot vertical) shall be determined by measuring from the toe of slope a distance of two-and-one-half times the channel depth plus thirty (30) feet. The structure setback line for unimproved channels with existing side slopes of 2.5:1 or flatter shall be thirty (30) feet measured from the top of bank.

3.

Channels twenty (20) feet deep and greater: the structure setback line for unimproved channels with existing side slopes steeper than 3:1 (three feet horizontal to one foot vertical) shall be determined by measuring from the toe of slope a distance of three times the channel depth plus twenty (20) feet. The structure setback line for unimproved channels with existing side slopes of 3:1 or flatter shall be twenty (20) feet measured form the top of bank.

D.

Structures and Landscaping Within Easements. No permanent structures of any kind other than drainage structures may be constructed within or over any easement described in this chapter. Landscaping, including trees and shrubs, may be planted within easements upon approval by the Public Works Department. The structure setback line shall be verified prior to the issuance of a building permit.

E.

Structures and Landscaping Within Structure Setback Areas. No permanent structures of any kind other than drainage structures may be constructed within, under or over any structure setback area described in this chapter. Fencing and landscaping, including trees and shrubs, are excluded from this restriction.

(CCCC§§ 914-10.402 — 914-10.410)

All levees and all ponding areas shall be completely contained within drainage easements.

(CCCC§ 94-10.602)

Disposal of stormwater drainage by means of ponding areas may be permitted only with the approval of the Public Works Department, after study of the proposed disposal basin topography and soil characteristics and only where no other reasonable method of disposal is feasible.

(CCCC§ 914-12.202)

Sub-drain facilities shall be provided where specified by the soil engineer controlling the work and other areas where deemed necessary by the city to prevent sliding or settlement of the earth surface. Facilities will be required to convey the subdrainage to an approved point of discharge.

(CCCC§ 914-12.402)

Chapter 16.68 - WATER AND SEWERS

Sections: