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• Mining has excessively lowered the thalweg elevation and altered the channel gradient in <br />parts of the pit, as described in the following section. <br />3.5 Changes in River Channel (Primarily from Mining) <br />• Between January of 1996 and January of 2003, parts of the thalweg have appazently <br />incised by a maximum of about 9 ft or aggraded by a maximum of about 2 ft (Table 2 and <br />Figure 1); the thalweg has incised more than 6 ft at three cross sections in the upper <br />middle part of the pit, but has incised very slightly at the upstream boundary and has <br />remained at essentially the same level near the downstream boundary; the average change <br />is incision of about 2.9 ft. <br />• Thalweg incision greater than 6 ft was first detected bypre-mining surveys during <br />September of 2001, and probably resulted from mining during the preceding Februazy <br />and Mazch; this local concavity in the channel had not filled by Januazy of 2003, when <br />the thalweg was even lower at two of these cross sections and at the same level in one. <br />• Since 1977, available data suggest that the thalweg has incised approximately 2-4 ft in <br />the upper part of the pit and 5-10 ft in the middle and lower parts of the pit (Table 2 and <br />Figure 1). Accuracy of the 1977 data is uncertain, but changes of this magnitude are <br />consistent with the relatively large height of the floodplain above the present channel. <br />• All of these changes in thalweg level are approximate because of geometrical projection <br />issues that arise from channel sinuosity and shifting channel locations; also, many cross <br />sections are oblique to the average trend of the channel belt or to existing channels; a <br />detailed analysis could improve estimates of thalweg elevation change. <br />• Sugnet Environmental states that the pit is in substantial compliance because thalweg <br />incision has exceeded the 6-ft limit in only a few places (Paul Sugnet to Kaza Hellige, <br />10/16/03); however, such deep incision is critical because it has occurred neaz the <br />upstream boundary of the pit, and is likely to greatly increase bank erosion at adjacent <br />properties. <br />• More specifically, Sugnet's longitudinal profiles suggest that a knickpoint (or locally <br />steepened portion of the channel) has developed in the upper part of the pit, immediately <br />upstream from the area of greatest thalweg lowering (contrary to the promise to maintain <br />the January 1996 channel gradient); this knickpoint appears to be shifting gradually <br />upstream by the natural process of headwazd erosion (or headcutting); if this process is <br />not controlled, it could severely increase erosion at other properties located upstream <br />from the pit during a period of yeazs to decades. <br />• Limited examination of aerial photographs suggests that Bar-D mining has already begun <br />to increase channel and bank erosion at upstream properties by lowering the thalweg <br />elevation and increasing channel sinuosity; this conclusion-is consistent with channel <br />changes shown on aerial photographs and with my field observations at James Ranch <br />roughly two yeazs ago. <br />Aerial photographs show major channel planform changes such as decreased channel <br />sinuosity and transformation of much of the former channel belt into a series of ponds <br />(Figure 2). <br />Gillam to Hellige, Nov. 28, 2003 page 6 <br />