EAC Littoral Zone Slope Criteria DEVELOPMENT SERVICES DEPARTMENT
PROJECT REVIEW SERVICES SECTION
MEMORANDUM
TO: EAB Members
FROM: Stephanie R. Smith, P.E.
Technical Services Supervisor
Barbara N. Prynoski
Chief Environmental Specialist
DATE: September 29, 1992
RE: Littoral Zone Slope Criteria
Staff is requesting the EAB discuss at the regular meeting
the slope criteria for littoral zones.
Attached is a copy of the excavation portion of the Land
Development Code which indicates the requirement for littoral
zones. Slope criteria was not added to the ordinance because
at the time the language was proposed, it was agreed to use
South Florida Water Management District rules.
Since that time, it has been determined that the South
Florida Water Management District has no written criteria.
South Florida Water Management District has used 6: 1 slopes
on projects in the past but are now indicating that 4 : 1 may
be acceptable. South Florida Water Management District has
not put this standard into the rules nor are they willing to
indicate the change in writing.
The littoral zone requirement was added to the Land
Development Code upon recommendation of Adhoc Committee
appointed to review the Land Development Code. Discussion
with Mr. Gary Beardsley and Mr. Todd Turrell indicated that
at the time Gary was thinking of a 6: 1 slope while Todd was
thinking of a 4 : 1 slope.
Project Review Services Engineering Staff has no opinion on
the requirement although we have held to the 6: 1 slope.
Project Review Services Environmental Staff recommends a 6: 1
slope. It must be kept in mind that the littoral zone is
required for only ten (10) percent of the lake' s edge. The
following reasons are offered in support of a 6: 1 slope:
* greater planting area increases water quality maintenance
capability and wildlife habitat;
* more accurately mimics a natural system;
* increases diversity of plants that can be planted; a
steeper slope would require a limited number of emergent
plant species that can tolerate the fluctuations of water
levels common in this area
* aesthetics; a 4 : 1 slope creates a narrow band that can be
described as a "vegetative bathtub ring" and
* safety.
EAB Members
10/29/92
Page 2
The request of Staff is that the EAB give direction as to
what slope should be used. There are two projects which are
objecting to the 6: 1 requirement on the basis that the loss
of fill material and added width of the lake needed to
accommodate the slope are too restrictive for the sites. The
difference in 6: 1 and 4 : 1 slope in quantity of fill material
is approximately 0.3 cubic feet per foot of littoral zone and
the width is 6 feet in the area of the littoral zone.
SRS/ew/doc: 5478
cc: EAB Binder
EAB File
Attachment
Division 3.5 Ezcavarion
3.5.7.2.3 In the event that property where a Commercial Excavation was previously excavated is
rezoned/developed for uses other than agriculture, the excavation shall be modified to the
standards for development excavations in accordance with the requirements of Sec. 3.5.7.2 proper,
or other criteria as may be more stringent.
3.5.7.2.4 Exceptions to the side slope requirements that may be justified by such alternatives as artificial
slope protection or vertical bulkheads shall be approved in advance by the Development Services
Director.
3.5.7.2.5 Ten percent (10%) of the finished lake banks shall be planted with natural aquatic vegetation on
a littoral shelf located three (3) feet vertically, with two-thirds (2/3) below and one-third (1/3)
above the control elevation.Littoral planting zones should be adjacent to and waterward of control
structures when possible.
3.5.7.2.6 No Building Construction Permits will be issued for any proposed construction around the
perimeter of any excavation where the minimum clearance between the excavation top-of-bank and
the proposed building foundation is less than 30 feet, unless and until all side slopes adjacent to
the proposed construction have been completed and approved by the Development Services
Director. Exceptions to this requirement will be made in those instances where the perimeter of
the excavation will be bulkheaded in accordance with the provisions of Sec. 3.5.7.2.4.
3.5.7.3 Depths. Unless site conditions, water quality or soil information indicates otherwise, the
excavation depths as measured from the permitted control elevation shall be as follows:
3.5.7.3.1 Maximum. Private and Development Excavations shall not exceed 12 feet in depth unless
computations using the "fetch formula" of maximum depth = 5 feet + (0.015)x (mean fetch in
feet) indicate that deeper depths are feasible. The mean fetch shall be computed as follows: ("A"
+ "B")/2 where "A" is the average length parallel to the long axis of the excavation and "B" is
the average width of the excavation as measured at right angles to the long axis.
Commercial Excavations shall not exceed 20 feet in depth unless otherwise supported by the "fetch
formula", or if it can be shown from a comparative water quality study that depths in excess of
20 feet will not, because of aquifer conditions or relative location to coastal saline waters, have
a detrimental effect on the groundwater resources in the surrounding area.
3.5.7.3.2 Minimum. In order to assure that unsightly conditions or undesirable aquatic growth will not
occur in wet retention areas during the dry season of the year, the bottom elevation of these
excavations shall be at least 6 feet below the mean annual low water level.
3.5.7.3.3 Over Excavation. In those instances where the excavator over-excavates the depth of the
excavation by more than an average of 10%, written justification shall be submitted to the
Development Services Director by the project's surveyor/engineer providing an assessment of the
impact of the over-excavation on the water quality of the excavation. If, upon review of the
assessment statement by the Development Services Director and Advisory Board, the increased
depth is found to be unacceptable, the Permittee shall be required to fill the excavation to the
permitted depth with materials and methods approved by the Development Services Director. If
the increased depth is deemed acceptable by the Development Services Director and approved by
the Environmental Advisory Board,a penalty will be assessed against the Permittee for the volume
Collier County 3-92 October 30, 1991
Land Development Code