from turbidity and the blanketing effects of sediment when they are cut 

 off from the river during low flows. An influx of groundwater from the 

 sandy eastern bluffs and sandy lake bottoms flushes away sediment de- 

 posited by the river. According to an Illinois Water Survey report 

 (Singh and Stall, 1973), this influx amounts to 309 cu ft/sec, or about 

 one-twelfth of the total input to this 73-mile section of the river, 

 during the lowest flow expected for a 7-day period at a recurrence in- 

 terval of 10 years. Matanzas Lake (mile 114.5-117.0) still exhibits a 

 recovery pattern, but mud now blankets the sandy bottoms in other lakes 

 such as Quiver Lake (mile 121.0-124.0), which once received spring water 

 (Richardson, 1921a). The influx of groundwater to these latter lakes 

 might still be sufficient to provide clear water if the bottoms could be 

 stabilized against wave action and the influx of sediment from the river 

 reduced or prevented. 



Another detrimental impact of the proposed increase in the depth 

 of the navigation channel would be the reduction in the capability of 

 the river to assimilate organic waste, due to increased time-of-travel, 

 reduced reaeration, and increased sedimentation (Butts, et al., 1975). 

 Land use in the drainage basin 



If predictive studies indicate that a reduction of sediment input 

 would actually reduce sedimentation in the river and the lakes and back- 

 waters, the most practicable solution to the sediment problem in the 

 future may be to reduce the amount entering the river. It is possible 

 that once sediment is in the river and lakes, it is recycled and re- 

 suspended there, and no reduction in turbidity or oxygen demand would 

 be achieved by reduction of sediment input, without the physical re- 

 moval of sediment or the use of restoration techniques, such as drying 

 out lakes. However, it is possible that reduced sediment input to the 

 river may cause the river to flush out backwater areas and lakes during 

 periods of high flow, thus bringing about a natural restoration of these 

 areas. Once the turbidity was reduced, fringing marshes and beds of 

 aquatic plants might appear again, further accelerating restoration by 

 acting as sediment filters and nutrient traps. 



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