Construction and Design Guidelines
Natural Streambed and Land Preservation Act
I. Bank Stabilization
- Vegetative Slopes
should be explored as the first method of bank stabilization. The preferred method of stabilizing a stream bank is to plant deep-rooted riparian
trees, shrubs and grasses. Riparian vegetation, the use of root wads and
tree revetments cause less ground and stream disturbance than traditional
riprap and are encouraged in order to maintain the quality of the stream and
See Links for Revegetation Sources
and erosion control blankets.
- Mimic nearby
stable bank areas where possible. As seen and elevation views, shape
should fit with existing stable banks up/down stream.
- A stabilized bank is one with a maximum
slope of 1½ :1. Another option is to create a wetland bench.
- Riprap rock shall be
angular and sized properly for the specific task unless otherwise specified.
On the Thompson Falls Reservoir, rock should
have an average diameter of 12 inches and be
placed no higher than 4 feet above normal full
pool of the reservoir, which is the typical late
summer, early fall elevation.
- All riprap rock shall
be reasonably free of silts, sands or fines.
- Prior to the placement of riprap, a graded
gravel should be used beneath the rock
to allow root penetration of vegetation. In areas where no vegetation is
desired, a filter fabric should be placed beneath the rock to inhibit erosion
of fines through the riprap.
- Unless otherwise specified, riprap rock should be toed-in below the mean annual high water line and be placed
at a maximum slope of 1½ :1. Rock should be placed on the bank, not
dumped, placing the largest rocks at the toe.
- Concrete for
riprap may be used only where structural strength a location dictate no other reasonable
- Retaining Walls
- Retaining walls can significantly alter
wave actions, currents, beach dynamics, bank erosion patterns, hydraulics, and
may affect neighboring property.
Therefore, retaining walls are the least desirable method of bank
stabilization. They are not recommended,
except in extreme cases.
- Retaining walls designed to extend the land area into the stream are
not permitted except under extreme circumstances. Each case will be considered individually.
II. Excavation or Filling of
stream should be preserved in its natural condition to the greatest extent
possible, in order to protect fish and wildlife
habitat and water quality. Increased
sedimentation in the stream
should be minimized to the greatest extend possible, as a protection for fish
habitat and water quality.
- Any material that is excavated from the
streambed or banks shall be removed entirely from the stream and floodplain and
deposited in such a manner to prohibit re-entry of the material into the
stream during high water.
stockpiling of excavated materials anywhere in the floodplain is prohibited except during active construction.
III. Erosion, Sedimentation and Storm Runoff
- Any construction activity that will affect the
stream bank should incorporate all
necessary means to minimize pollution of the stream, including erosion,
sediment, and storm runoff controls.
- The proposed activity should minimize increased
sedimentation, an increase in suspended sediments, or an increased discharge of
nutrients into the stream either during its construction or utilization.
Unless otherwise approved, the interface of fill
materials, such as riprap, with the stream water shall be sloped at a maximum
of 1 ½: 1 ratio in order to dissipate wave and stream flow energy. The face of the slope shall be covered with
suitable materials to discourage soil erosion and slumping of banks.
The natural protective armament of the stream
and stream bank shall be preserved wherever possible. Natural vegetation shall be preserved
wherever possible and as specified in the rules adopted under Montana’s Natural Streambed and Preservation Act (310 Law).
Vegetation shall be
required as a means of stabilizing erosive areas. Deep-rooting native
vegetation (shrubs/trees) are preferable over grasses to provide soil
stability. Erosion blankets are useful to provide temporary protection and aid
in plant establishment. Seed grass
before blanket is placed.
See Links for
and erosion control blankets.
will be limited to those actions authorized in the 310 permit and controlled by
the Natural Streambed and Preservation Act (310 Law).
Burning of materials on the streambed or banks will cause a
degradation of water quality, and may create safety hazards. Burning weeds, grass, shrubs, brush, trees,
old construction materials, debris from new construction or similar materials
on the streambed or banks is not allowed below the mean high water line.
IV. Dredge, Fill and Swim Beach
- Dredging of a
streambed or bank may result in suspension of fine materials, re-suspension of
nutrients and toxic materials, exposure of stable streambed sediments to
unstable conditions, removal of streambed armament and creation of steep bench
- Filling of wetlands
that are located on the immediate bank may result in the destruction of an
aquatic environment, loss of habitat for fish and wildlife, loss of water
storage capacity and loss of the natural storm runoff cleansing functions and
the natural nutrient entrapment functions of wetlands.
- Dredging for the
purpose of creating, enlarging, or improving an artificial harbor, lagoon, or
in-stream pond is not permitted in most cases.
- In cases where dredging is allowed, areas shall
be stabilized with a protective armament as soon as possible after excavation. In areas
where there is a rock layer on the surface of the streambed or bank, such rock
shall be removed and set aside, then replaced as a protective layer subsequent
to the excavation.
- Dredging and/or filling is only permitted at the
time of year specified on the permit
projects for the purpose of expanding existing land areas are not allowed.
- Discharge of fill material into the stream is
generally not allowed.
of wetlands is discouraged and will be considered on a case by case basis.
- Filling for the
purpose of creating a swimming beach may be allowed on a case by case
basis. All fill, if allowed, shall be
clean, washed material free of silts and fines.
V. Construction Materials (Apply to all projects)
- General Considerations
leach over time and degrade water quality.
While metals are
generally inert except for oxidation, surface applications of some foreign
material (i.e. wet paint, grease, oil, etc.,) can degrade water quality.
Any building material
should be stable and free of silts, sands, fines, chemical preservatives,
grease, oil or any surface application which could immediately or eventually
contaminate water quality.
- All wood used shall be
left in its natural state unless treatments meet current standards for the
Department of Environmental Quality.
Application of paint
or stain is accepted as a routine maintenance measure for any structure built
prior to 1995 or as authorized since that date located landward of the mean
high water line which has been painted or stained on a routine basis in the
- Where wood is used for
any project which would at sometime be in, or over the water, only solid wood
shall be used. Wood that is not solid,
such as plywood, particle board, chipboard, unless specially designed for marine
use, should be avoided and may be subject to board approval.
Any metal used may be
painted or coated with an inert metal sealant, (such
as lead-free paint, plastic, rubber, enamel) which has thoroughly dried/cured
prior to its use.
Minimal lubrication of
critical metal components may be used where necessary
No metal used in the
project area may contain deposits or a surface application
of the following:
Grease or oil, except
for necessary lubrication.
Paint, varnish or
coatings which have not thoroughly cured or dried
Any chemical or
substance which will wash off or dissolve when in contact with water.
Foam Flotation Logs
When molded foam or
other floating material is used in a dock design, it must be enclosed or sealed
to avoid break-up and/or scattering of loose material. If this occurs, the source must be repaired
as soon as possible.
All foam flotation
logs shall be completely encased in solid wood or in metal. Drain holes or a maximum of ½ inch spacing
between wood boards may be allowed.
Asphalt: Asphalt or similar petroleum based products
intended for use as a travel or walking surface should be avoided.
Concrete rubble is the
least desirable construction material in relation to wood, stone and should be
used only where structural strength and location dictate no other reasonable
Wet concrete shall not
be poured into or allowed to come in contact with the water. On a case-by-case-basis, concrete poured
within water-tight forms may be approved.
Rock or Stone: rock or stone is a natural material for
construction. All rock or stone which
will come in contact with the stream shall be reasonably free of silts, sands
Design Guidelines for Facilities
I. General Considerations
stream bank dock facilities shared by two or more owners are encouraged, as such facilities
shall reduce the overall environmental impacts on the streambed and bank and
ease navigational congestion on the stream.
docks will be reviewed on an on-site basis.
The following, among other things will be considered:
Docks should be removed from the water during periods of high annual flow and
anchored securely above the mean high water line to avoid drift.
in the area of a stream will be such as not to concentrate run-off into the stream.
- Marinas, because of their
size, have a high potential to impact the stream and stream bank. A marina should be designed to accommodate
only its anticipated sizing and capacity needs, to protect the navigational
rights and safety of neighboring property owners and recreational users of the
water resource, and to protect the quality of the water and fish and wildlife
marinas will be reviewed on an on-site basis.
The following with be considered:
III. Boathouses, Boat Shelters and
structures are essentially land based structures and, where built within the stream, have a high potential
to significantly alter the natural characteristics of the shoreline and
diminish water quality.
streambed and bank shall not be excavated, dredged, or filled in order to provide channels and suitable
water depth for boating access to a structure.
in the area of a stream will be such as not to concentrate run-off Into the stream.
IV. Boat Ramps and Boat Rail Systems
ramps have a potential to increase sedimentation in the stream and diminish water quality.
rail systems, if properly installed, generally have an insignificant impact on the stream and its banks.
designed for removal of boats from a stream, such as rail systems, are preferred to attempting to
build a dock, shore station, or boat shelter for protection of boats, as the
overall impacts tend to be less adverse.
and/or the base of the boat ramp shall be constructed below the pre-existing grade of the stream bank.
material excavated from the stream to construct the boat ramp and not used as
ramp foundation material shall be immediately and completely removed from the
floodplain and deposited in such a manner as to prohibit its re-entry into the
ramps shall be of the same elevation as the pre-construction streambed and
banks, except that maximum grade shall not exceed 15 percent regardless of the
boat ramp edges shall be thickened to a minimum of twice the average thickness
of the ramp in order to prevent erosive undercutting or breaking of ramp edges.
rails shall be suitably anchored to the stream bottom.
rails of the rail launching system shall not exceed four (4) inches in height
and the rail system shall lie on and follow the grade of the existing streambed
and banks. No portion of the rail shall
extend more than 18 inches above the immediately adjacent land.
V. Utility Lines
(Electrical, Sewer, Water, Wells)
placement and maintenance of utility lines and wells, if done improperly, can have significant effects on
streams due to disturbance of the streambed or banks.
sewage pump-out facilities may be placed in public or private marinas or public parks.
facilities shall include equipment to pump or otherwise receive and transfer contents of vessel
holding tanks into a sewage retention and/or disposal system located outside
Waterlines: That portion of the waterline which is not
buried and lies exposed on the bottom of the streambed or bank shall be
weighted to prevent floatation or snagging.
well or cistern shall be drilled or developed in the stream.
wells or cisterns located near a stream, when originally developing and pumping
the well, the silt laden water shall not be allowed to flow into the stream.
the minimum amount of material necessary to lay the line shall be removed from
material excavated from the trench shall be replaced back into the trench as
backfill. Any material that is not
replaced back into the trench shall be completely removed from the floodplain.
areas where there is a rock layer on the surface of the streambed or bank, such
rock shall be removed and set aside, then replaced as a protective layer
subsequent to the excavation.
areas where no rock layer exists, the replaced dirt shall be compacted and
consolidated in order to prevent erosion.
Additional cover, such as gravel, a rock layer or vegetation, may also
installation, the streambed or bank shall be returned to its condition prior to
VI. Fuel Tanks
spills into the stream can create serious water quality hazards and may impair fish and wildlife habitat.
Bulk fuel tanks should not be
placed over or under a stream or its immediate
If a tank is located near a stream and the
line goes under, through, or over a stream, an appropriate device shall be
installed to prevent a leak in the line from draining into the stream.
VII. Dwelling Units
concentrations of human activities. Such
activities are essentially
land based with people entering the aquatic environment only for relatively
short periods of time for recreational purposes. Buildings are potentially harmful through
creation of impervious surfaces, increasing surface runoff in the stream and
possible sewer leakage.
buildings or portions thereof over a stream or the immediate banks of
a stream should be avoided. This
includes roof overhangs, drip lines, balconies, bay windows, and chimneys.
Building in the
floodplain is discouraged.
- Fences along streams or livestock watering
areas may require a 310 permit. Contact Green
Mountain Conservation District for more information.
- Fences should not be constructed across
IX. Decks, Walkways and Stairways
Decks, walkways and
stairways are all structures which are located landward of mean
high water and are considered as constructed surfaces.
If properly placed and
constructed these structures typically have minimal impact
on the stream bank and in some cases, help to protect the fragile shoreline
from foot traffic.
Projects for decks,
walkways, and stairways will be reviewed on a case by case
basis taking into consideration the following:
will be constructed so as not to concentrate runoff into the stream.
Structures shall be constructed
on the existing terrain. Stones, gravel
or wood are
recommended travel surfaces as opposed to concrete.
X. Culverts and Bridges
Choose a crossing site
in a stable, relatively straight reach of channel where possible. A deep, narrow crossing is preferred to a
wide, shallow location.
Cross the stream
perpendicular to the channel whenever possible.
Bridges are preferred
to other types of crossings because they allow fish passage and minimize
changes to the stream channel and floodplain.
should allow for the passage of 100-year flood events and be bankfull width
(the width the stream is during a 1.5 to 2-year flood event). This minimizes changes to the stream channel
caused by the structure and usually allows adequate capacity to transport
If a culvert is used,
the culvert should be placed one to two feet below existing stream grade to
facilitate fish passage. Grade control
should also be placed at the upper and lower ends of the culvert to prevent headcuts
from forming if the channel substrate is flushed out of the culvert during high
If a culvert is used,
the inlet and outlet of the pipe should be armored with rock to prevent
on the design and construction of culvers and bridges is available at the Green
Mountain Conservation District office.
XI. Off-Stream Ponds
An off-stream pond is
one that is built off the stream channel itself and diverts water
from the adjacent stream.
off-stream ponds contribute to poor water quality and raise potential
for stream channel changes.
Ditches, headgates, or
water intakes on a perennial channel or stream but used for off-stream
ponds require a 310 permit. A form 270
is required for an inlet or outlet to an off-stream pond.
Off-stream ponds are
discouraged. Off-stream ponds can increase the water temperature and reduce
water quality for fish in the stream downstream of the pond.
An instream fish
filtration system must be designed to prevent instream fish access to the pond
and prevent access of fish from the pond to the stream.
If allowed, the
diversion shall be connected to the stream by means of a buried pipeline fitted
with the inlet and outlet controls.
Off-stream ponds will
be designed to meet water quality standards set by the Department of
XII. Other Projects
types of projects that are not specifically covered by the forgoing guidelines
shall be reviewed on an individual basis.