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‘The Thin Green Line’
There are many rules that limit what can be done on public waterways and the adjoining shoreland. These rules are designed to protect water quality, wildlife, safety and enjoyment of the waterway. They can determine where you place your dock or how far you build from the shoreline.
In Minnesota, public waterways that border agricultural fields also have rules that affect their use and the use of the adjoining shoreland. On a lake, shoreland area extends 1000 feet from the high water level and parallel to the lakes’ shoreline. In most areas, row crop farming can take place.
However in the shoreland area of streams classed as protected waters, all areas within 50 feet from the high water level and parallel to the shoreline must be maintained in permanent vegetation as indicated in Minnesota state rule 6120.3300. This vegetated strip is commonly called a buffer.
A buffer is planted with perennial vegetation to slow down any possible runoff from the neighboring field. Field runoff can contain sediment and nutrients that can severely damage surface water near at hand or far downstream. By slowing the runoff down, excess sediment and nutrients can be filtered out of the water before it drains into the waterway. The DNR provides these rules to counties to be adopted into their land use ordinances. The county has the responsibility to enforce the minimum requirements.
At a recent discussion at the Lake Pepin TMDL meeting on June 4th, the point was raised that a 50 foot buffer is not always or even usually an adequate solution to rural runoff. Yet, the 50-foot buffer is a very useful tool for ensuring that the worst forms of runoff are kept under control:
Norm Senjem offered this explanation:
The concept of the "thin green line" broadens the discussion of the role of the 50 foot buffer:
It is true that a 50 foot vegetative buffer will not stop or retard or filter surface runoff or intercept shallow groundwater flows of dissolved nutrients or pesticides in a great many cases, such as in proximity to steep slopes. However, the concept of the thin green line is to view the 50 foot buffer as a sign that upstream runoff is adequately controlled, because the presence of an intact buffer is evidence that channelized flow is not coming from the adjacent field; that all flow is coming by sheet or rill, which is the kind of runoff a buffer is designed to filter. So, the 50 foot filter is both a practice that treats runoff and an indicator of the adequacy of upslope conservation practices.
It is also true that a 50 foot buffer is not needed along every inch of protected waters to provide runoff filtering -- where berms etc. may be present. However, the presence of berms, especially along drainage ditches, seldom offers complete protection from runoff. If berms create the ponding of water in low spots of the fields, these will be overtopped, leading to channel erosion, during high-precip events. Also, in order to avoid prolonged ponding of water, which suffocates crops, farmers often install side inlets which drain water from the pond to the ditch, often with little or no protection around the surface intake. Poorly designed side inlets defeat the purpose of the 50 foot buffer, and should be placed within grassed swales or waterways connected to the buffer.
An additional, important, value of the 50 foot buffer is the terrestial habitat it provides as complementary to the aquatic habitat. A stream that is only a slit through a tilled field is not a healthy stream. A stream includes terrestial components that interact with the water world interdependently to produce a richer habitat for birds, insects, mammals, etc.
As shown in the diagram below, the 50-foot shore impact zone is one of several setbacks required on agricultural land. Others include a 66-foot setback for atrazine applications, and a 100 foot setback for manure applications that are not incorporated within 24 hours.
There are many rules that limit what can be done on public waterways and the adjoining shoreland. These rules are designed to protect water quality, wildlife, safety and enjoyment of the waterway. They can determine where you place your dock or how far you build from the shoreline.
In Minnesota, public waterways that border agricultural fields also have rules that affect their use and the use of the adjoining shoreland. On a lake, shoreland area extends 1000 feet from the high water level and parallel to the lakes’ shoreline. In most areas, row crop farming can take place.
However in the shoreland area of streams classed as protected waters, all areas within 50 feet from the high water level and parallel to the shoreline must be maintained in permanent vegetation as indicated in Minnesota state rule 6120.3300. This vegetated strip is commonly called a buffer.
A buffer is planted with perennial vegetation to slow down any possible runoff from the neighboring field. Field runoff can contain sediment and nutrients that can severely damage surface water near at hand or far downstream. By slowing the runoff down, excess sediment and nutrients can be filtered out of the water before it drains into the waterway. The DNR provides these rules to counties to be adopted into their land use ordinances. The county has the responsibility to enforce the minimum requirements.
At a recent discussion at the Lake Pepin TMDL meeting on June 4th, the point was raised that a 50 foot buffer is not always or even usually an adequate solution to rural runoff. Yet, the 50-foot buffer is a very useful tool for ensuring that the worst forms of runoff are kept under control:
Norm Senjem offered this explanation:
The concept of the "thin green line" broadens the discussion of the role of the 50 foot buffer:
It is true that a 50 foot vegetative buffer will not stop or retard or filter surface runoff or intercept shallow groundwater flows of dissolved nutrients or pesticides in a great many cases, such as in proximity to steep slopes. However, the concept of the thin green line is to view the 50 foot buffer as a sign that upstream runoff is adequately controlled, because the presence of an intact buffer is evidence that channelized flow is not coming from the adjacent field; that all flow is coming by sheet or rill, which is the kind of runoff a buffer is designed to filter. So, the 50 foot filter is both a practice that treats runoff and an indicator of the adequacy of upslope conservation practices.
It is also true that a 50 foot buffer is not needed along every inch of protected waters to provide runoff filtering -- where berms etc. may be present. However, the presence of berms, especially along drainage ditches, seldom offers complete protection from runoff. If berms create the ponding of water in low spots of the fields, these will be overtopped, leading to channel erosion, during high-precip events. Also, in order to avoid prolonged ponding of water, which suffocates crops, farmers often install side inlets which drain water from the pond to the ditch, often with little or no protection around the surface intake. Poorly designed side inlets defeat the purpose of the 50 foot buffer, and should be placed within grassed swales or waterways connected to the buffer.
An additional, important, value of the 50 foot buffer is the terrestial habitat it provides as complementary to the aquatic habitat. A stream that is only a slit through a tilled field is not a healthy stream. A stream includes terrestial components that interact with the water world interdependently to produce a richer habitat for birds, insects, mammals, etc.
As shown in the diagram below, the 50-foot shore impact zone is one of several setbacks required on agricultural land. Others include a 66-foot setback for atrazine applications, and a 100 foot setback for manure applications that are not incorporated within 24 hours.
Source: Cannon River Watershed Partnership website.
For further information on MN Laws for Stream Buffers in Agricultural Areas click here.
QUESTION:
This is in regard to a grant the MN Science Museum has received to study the sediment problem in our rivers. It appears that the Museum's study (although the draft of its findings is not complete) shows that bank erosion (slumping, breaking away, flooding, etc.) is the main culprit - not runoff from farm field - to cause sediment to be deposited in the Mississippi . . . that the runoff from fields is relatively the same as it has been for the past sixty years. What impact if any will this study have?
ANSWER:
Dan Engstrom's research has indeed demonstrated that sediment being deposited in Lake Pepin is about evenly divided among three sources: river bluffs & banks, ravines that connect fields to streams down steep hillsides, and traditional field erosion. I've been promoting the concept of "the thin green line" to suggest that the stream buffer be viewed as more than a simple Best Management Practice, the effectiveness of which is limited by up-slope runoff and the degree to which it is converted to sheet or rill flow by conservation measures. The revised shoreland rule is carefully worded to specify continuous as well as permanent vegetative cover of the 50 foot shoreland impact zone. Breaches of the 50 foot buffer would thus constitute non-compliance. To return to compliance, landowners would need to treat upland runoff so as to ensure that only sheet and rill erosion encounters the buffer, up to some maximum specified precip event. In this manner, shoreland compliance could be used to address field runoff and ravines -- two thirds of the sediment source -- while also making a dent in bluff/bank erosion.
----- Norm Senjem
This is in regard to a grant the MN Science Museum has received to study the sediment problem in our rivers. It appears that the Museum's study (although the draft of its findings is not complete) shows that bank erosion (slumping, breaking away, flooding, etc.) is the main culprit - not runoff from farm field - to cause sediment to be deposited in the Mississippi . . . that the runoff from fields is relatively the same as it has been for the past sixty years. What impact if any will this study have?
ANSWER:
Dan Engstrom's research has indeed demonstrated that sediment being deposited in Lake Pepin is about evenly divided among three sources: river bluffs & banks, ravines that connect fields to streams down steep hillsides, and traditional field erosion. I've been promoting the concept of "the thin green line" to suggest that the stream buffer be viewed as more than a simple Best Management Practice, the effectiveness of which is limited by up-slope runoff and the degree to which it is converted to sheet or rill flow by conservation measures. The revised shoreland rule is carefully worded to specify continuous as well as permanent vegetative cover of the 50 foot shoreland impact zone. Breaches of the 50 foot buffer would thus constitute non-compliance. To return to compliance, landowners would need to treat upland runoff so as to ensure that only sheet and rill erosion encounters the buffer, up to some maximum specified precip event. In this manner, shoreland compliance could be used to address field runoff and ravines -- two thirds of the sediment source -- while also making a dent in bluff/bank erosion.
----- Norm Senjem
Do you have a question about the 50 foot buffer (thin green line) or any other issue related to the deposit of sediment in Lake Pepin?
Send us your question and we'll do our best to provide an answer on line.
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Send a question
Send us your question and we'll do our best to provide an answer on line.
Names will not be posted.
Send a question