310 Guidelines

for the Natural Streambed and Land Preservation Act (310 Law)

I. Bank Stabilization

  1. Vegetative Slopes
    1. Vegetation 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 its banks.
      See Links for Revegetation Sources and erosion control blankets.
    2. Mimic nearby stable bank areas where possible. As seen and elevation views, shape should fit with existing stable banks up/down stream.
    3. A stabilized bank is one with a maximum slope of 1½ :1.  Another  option is to create a wetland bench.
  2. Rip Rap
    1. 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.
    2. All riprap rock shall be reasonably free of silts, sands or fines.
    3. 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.
    4. 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.
    5. Concrete for riprap may be used only where structural strength a location dictate no other reasonable alternative.
  3. Retaining Walls
    1. 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.
    2. 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 Materials

  1. The 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.
  2. 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.
  3. Temporary stockpiling of excavated materials anywhere in the floodplain is prohibited except during active construction.

III.   Erosion, Sedimentation and Storm Runoff

  1. 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.
  2. 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.
  3. 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.
  4. 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).
  5. 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 Revegetation Sources and erosion control blankets.
  6. Mechanized equipment will be limited to those actions authorized in the 310 permit and controlled by the Natural Streambed and Preservation Act (310 Law).
  7. 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 Creation

  1. 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 areas.
  2. 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.
  3. Dredging for the purpose of creating, enlarging, or improving an artificial harbor, lagoon, or in-stream pond is not permitted in most cases.
  4. 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.
  5. Dredging and/or filling is only permitted at the time of year specified on the permit
  6. Fill projects for the purpose of expanding existing land areas are not allowed.
  7. Discharge of fill material into the stream is generally not allowed.
  8. Filling of wetlands is discouraged and will be considered on a case by case basis.
  9. 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)

  1. General Considerations
    1. Wood preservatives leach over time and degrade water quality.
    2. 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.
    3. 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.
  2. Wood
    1. All wood used shall be left in its natural state unless treatments meet current standards for the Department of Environmental Quality.
    2. 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 past.
    3. 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.
  3. Metal
    1. 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.
    2. Minimal lubrication of critical metal components may be used where necessary for movement.
    3. 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.
  4. Foam Flotation Logs
    1. 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.
    2. 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.
  5. Asphalt:  Asphalt or similar petroleum based products intended for use as a travel or walking surface should be avoided.
  6.  Concrete
    1. 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 alternative.
    2. 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.
  7. 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 or fines.



I. General Considerations

  1. Common 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.
  2. All docks will be reviewed on an on-site basis.  The following, among other things will be considered:
    • Current
    • Water depth
    • Stream width
    • Stream configuration
    • Soils
    • Bank configuration
  3. Floating 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.
  4. Construction in the area of a stream will be such as not to concentrate run-off into the stream.

II. Marinas

  1. 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 habitat.
  2. All marinas will be reviewed on an on-site basis.  The following with be considered:
    • Current
    • Water depth
    • Stream width
    • Stream configuration
    • Soils
    • Bank configuration

III.  Boathouses, Boat Shelters and Shore Stations

  1. These 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.
  2. The 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.
  3. Construction 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

  1. Boat ramps have a potential to increase sedimentation in the stream and diminish water quality.
  2. Boat rail systems, if properly installed, generally have an insignificant impact on the stream and its banks.
  3. Facilities 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.
  4. Footings and/or the base of the boat ramp shall be constructed below the pre-existing grade of the stream bank.
  5. All 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 stream.
  6. Boat 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 stream bank.
  7. Concrete 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.
  8. Launching rails shall be suitably anchored to the stream bottom.
  9. The 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)

  1.  The 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.
  2. Sewer line/Disposal facilities
    1. Streamside sewage pump-out facilities may be placed in public or private marinas or public parks.
    2. Such 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 the floodplain.
  3. 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.
  4. Wells and cisterns
    1. No well or cistern shall be drilled or developed in the stream.
    2. For 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.
  5. Utility Line Burial
    1. Only the minimum amount of material necessary to lay the line shall be removed from the trench.
    2. All 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.
    3. 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.
    4.  In 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 be required.
    5. Following installation, the streambed or bank shall be returned to its condition prior to construction.

VI. Fuel Tanks

  1. Fuel spills into the stream can create serious water quality hazards and may impair fish and wildlife habitat.
  2. Bulk fuel tanks should not be placed over or under a stream or its immediate banks.
  3. 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

  1. Buildings represent 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.
  2. Construction of 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.
  3. Building in the floodplain is discouraged.

VIII.  Fences

  1. Fences along streams or livestock watering areas may require a 310 permit.  Contact Green Mountain Conservation District for more information.
  2. Fences should not be constructed across streams.

IX. Decks, Walkways and Stairways

  1. Decks, walkways and stairways are all structures which are located landward of mean high water and are considered as constructed surfaces.
  2. 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.
  3. Projects for decks, walkways, and stairways will be reviewed on a case by case basis taking into consideration the following:
    • Bank configuration
    • Bank slope
    • Soil stability
    • Other site-specific items
  4. Structures allowed, will be constructed so as not to concentrate runoff into the stream.
  5. Structures shall be constructed on the existing terrain.  Stones, gravel or wood are recommended travel surfaces as opposed to concrete.

X. Culverts and Bridges

  1. 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.
  2. Cross the stream perpendicular to the channel whenever possible.
  3. Bridges are preferred to other types of crossings because they allow fish passage and minimize changes to the stream channel and floodplain.
  4. Crossing structures 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 debris.
  5. 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 flow events.
  6. If a culvert is used, the inlet and outlet of the pipe should be armored with rock to prevent scouring.
  7. Additional information on the design and construction of culvers and bridges is available at the Green Mountain Conservation District office.

XI. Off-Stream Ponds

  1. An off-stream pond is one that is built off the stream channel itself and diverts water from the adjacent stream.
  2. Done improperly, off-stream ponds contribute to poor water quality and raise potential for stream channel changes.
  3. 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.
  4. 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.
  5. 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.
  6. If allowed, the diversion shall be connected to the stream by means of a buried pipeline fitted with the inlet and outlet controls.
  7. Off-stream ponds will be designed to meet water quality standards set by the Department of Environmental Quality.

XII. Other Projects

Other types of projects that are not specifically covered by the forgoing guidelines shall be reviewed on an individual basis.