HNA Summary Report
Forecast Future Condition

Quantitative Geomorphic Change
The plan form features of the UMRS are quite stable and are not projected to change much in absolute area over the next fifty years. The projected changes for all the pools along the UMR include a prediction that total water area will decrease by only 1.4 percent by the year 2050. The area of aquatic area classes is predicted to change as follows:

• contiguous backwaters decrease by 2.1%;
• isolated backwaters decrease by 3.6%
• main channel decreases by 0.7%;
• secondary channels decrease by 2.6%;
• island area decreases by 2.0%.

Island loss is largely due to island erosion predicted to occur in Reach 3. For many other reaches, the area of islands actually increases. Overall, the total perimeter of islands is predicted to decrease by 3.7%. The acreage change predictions should not be considered to be precise estimates of change, but should rather be considered as indicators of the types and general amounts of changes likely to occur in the future. Also, it must be emphasized that the predictions include changes in surface area only, and do not account for many factors that affect habitat quality.

The Cumulative Effects Study projected geomorphic change for much of the UMRS and concluded that Reach 3 (Pools 5-9) has been and is predicted to continue to be dominated by island erosion. Reach 3 (Pools 5-9) is the only reach where total open water area is expected to increase. This is due to the predicted continued erosion of islands in the reach. In all other reaches, total water area is expected to decrease, including both isolated and contiguous backwater areas.

Geomorphic Change Processes
The Cumulative Effects Study identified 58 locations in pools 4 through 26 influenced by one or more of nine geomorphic processes. Consultations with resource managers yielded an additional 347 areas in the same reach and an additional 125 areas in Pools 2-3, the Open river, and the Illinois River. A total of 530 areas expected to change were plotted on maps (Fig. 26; Table 5).

Fig. 26. Resource managers identified areas expected to change throughout the UMRS similar to this example from Pool 7 near La Crosse, Wisconsin.

Floodplain Vegetation Succession
Open water and scrub-shrub habitats are projected to decline. No change is predicted for grassland, agriculture, and developed area. Small increases are projected for wet meadow. Rather large changes are projected for early successional stage communities (i.e., willows and cottonwoods). Increased sand-mud is due to loss of open water area. The simple rule-based terrestrial vegetation successional model probably overestimates the amount of early successional species likely to occur on the UMRS.