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<br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br /> <br />channel may have been altered by instream mining, which causes incision and <br />accelerated bank erosion. Removal of riparian vegetation, bulldozing in the main channel, <br />irrigation diversions and return flows, urbanization, bridge construction, and restrictions <br />on the channel's lateral mobility have all occurred in the lower reach. The cumulative <br />impact of human activities in the lower reach appears to be increased channel instability <br />and bank erosion along the North Fork of the Gunnison River. <br /> <br />Rehabilitation efforts should focus on providing space for lateral channel <br />adjustment; reducing human activities that increase stream bed and bank erosion; and <br />facilitating the regrowth of riparian vegetation. Recommended additional studies include <br />developing a sediment budget for suspended sediment in order to quantify the sediment- <br />trapping effect ofPaonia Reservoir, and sediment sampling and cross-section monitoring <br />in both the upper and lower reaches of the study area in order to quantify channel <br />response to both changes in flow and sediment regime and human activities. <br /> <br />The next section is a response to five specific questions posed by Crane and Hyde <br />during the course of the North Fork Gunnison River study. <br /> <br />I What have we learned? <br />The results of the research conducted during 2001-2002 can be summarized under <br />two points. <br />1) The North Fork Gunnison River from just upstream ofPaonia downstream to <br />Hotchkiss has been predominantly braided throughout recent history. Aerial photographs <br />dating back to 1939, and historical records back to the late 1800s, suggest that the <br />channel has been broad and shallow, with multiple, shifting flow paths, throughout the <br />past one to two hundred years. The presence of cottonwood trees that germinated in <br />gravel, rather than finer sediments, suggests that at the time of germination (late 1800s- <br />early 1900s) the floodplain was fairly flat and had a high water table. These conditions <br />are characteristic of braided river systems. In addition, examination of the valley gradient, <br />valley confinement, natural sediment supply, and fluctuations in flow downstream from <br />Paonia suggest that the North Fork Gunnison River is likely to have had a braided pattern <br /> <br />4 <br />