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Broken
Stream Banks

Failure to maintain buffer zones worsens farm pollution

 
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Drainage Ditches and Intermittent Streams are Hardest Hit

Broken Stream Banks: Drainage Ditches and Intermittent Streams are Hardest Hit

April 25, 2014

EWG found that drainage ditches and intermittent streams that are even more directly connected to row crop fields are the least well protected waterways. However, we were unable to complete a comprehensive assessment of buffers along public ditches – drainage ditches under State jurisdiction – and intermittent streams because of time and resource constraints and because many – perhaps most – miles of public ditches do not appear on the Public Waters Inventory GIS layer. The coverage of intermittent streams is even less adequate.

Public Ditches

The GIS layer identifies more than 4,412 miles of public ditches statewide.25 EWG analyzed a sub- sample of the seven watersheds in southern Minnesota that have more than 20 miles of public ditch associated with cropland, according to the Public Waters Inventory’s GIS layer. (Figure 8)

Figure 8: Watersheds Evaluated for Buffers Along Public Ditches and Intermittent Streams Identified in the Public Waters Inventory GIS Layer 

 

The Minnesota Center for Environmental Advocacy (MCEA) has built a more detailed and comprehensive GIS layer of waterways.26 The Center’s analysis evaluated public waterways adjacent to all land cover types. Given the enormity of the task, the Center limited its assessment of the presence or absence of buffers to Blue Earth County and the Middle Minnesota, Cedar River, Sauk River, Root River and Pomme de Terre watersheds (Figure 8). The analysis yielded a detailed atlas classifying adjacent land cover types for all public waters in more than 200 watersheds. The study found that, on average, only 51 percent of the acres within 50 feet of the ditch banks were buffered.

EWG looked at an entirely different and smaller set of 189 miles of public ditches that bordered cropland, but our results are remarkably consistent with the Center’s findings. EWG found that 99 percent of the 16.5 feet of buffer required by Minnesota’s drainage law was maintained along the public ditches we assessed. In contrast, only 55 percent of the acres within 50 feet of the ditch banks were buffered – a failing grade under the far more protective shoreland management rule. Five of the seven watersheds we investigated also got a failing grade for maintaining buffers along public ditches that were far narrower than 50 feet (Table 2). The remaining two watersheds earned a D and a C. 

Table 2: Ditches in Five of Seven Watersheds Got Failing Grades

Watershed Name Grade Percent of 50-foot Buffer Present Buffer Acres Missing Buffer Acres Present
Headwaters Tenmile Creek F 48% 104 94
Stony Run Creek F 56% 72 93
City of Raymond-Hawk Creek D 60% 31 47
County Ditch No. 15 F 50% 64 63
Upper Le Sueur Creek F 56% 56 72
Judicial Ditch No. 13 F 51% 45 47
County Ditch No. 11 C 74% 21 62
Total F 55% 393 478

 

Intermittent Streams

Figure 9: Intermittent Streams Become Gullies in Crop Fields.



Source: ESRI, Digital Globe

Intermittent streams in the Public Waters Inventory GIS layer present an even more troubling picture. Many of the waterways classified as intermittent no longer have a defined bed or banks. They have been plowed over and are fully part of a row crop field (Figure 9). Some of these intermittent streams are well buffered, and others have a grassed waterway that follows the course of the stream. But many have no protection at all.

EWG surveyed the three watersheds with more than 30 miles of intermittent streams in the Inventory’s GIS layer (Figure 8), a total of 106 miles in all. All three got a failing grade. (Table 3) On average, only 54 percent of the acres within 50 feet of these streams were buffered. Moreover, the vegetative buffers tended to be either completely present or completely absent.

 

Table 3: Intermittent streams in all three assessed watersheds got failing grades

Watershed Name Grade Percent of 50-foot Buffer Present Buffer Acres Missing Buffer Acres Present
Upper Beaver Creek F 54% 48 57
Upper Flandreau Creek F 53% 14 16
Willow Creek-Flandreau Creek F 52% 27 29
Total F 54% 89 102