Rock Island Ecological Services Office
Midwest Region



Description of Pool 16:

Pool 16 is about 25 miles in length from Muscatine, Iowa to Rock Island, Illinois, approximate river miles 457.2 to 483.  Based on 1989 aerial photography, the Upper Mississippi River Environmental Program Habitat Needs Assessment (HNA) calculated 26,821 acres in 18 land cover classes, including open water for this pool. Pool 16 is one of two hinge-point operated navigation pools in the Rock Island District.  Hinge point operation was selected for this river segment to minimize the overflow/inundation area required for impoundment and consequent land acquisition for the 9-Foot Channel Project.

Forest resources on Federal lands in Pool 16 are managed by the Corps of Engineers, with wildlife and fisheries managed primarily by the States of Illinois and Iowa.  There is one area managed by the Scott County Conservation Board, and one area managed by the Iowa Department of Natural Resources.

One major tributary, the Rock River, with a watershed of 10,915 square miles[1] enters upper Pool 16 west of Rock Island at approximate river mile 479.  The confluence of the rock with the Mississippi formed a large delta island complex referred to as Big Island and was once defined by the main channel of the Rock and separate braided channels and sloughs.  During the historic period, these channels, sloughs, and riparian lancover types have been altered, filled, and conveted to agriculture, aggregate mining, urban development, and infrastructure rights-of-way.

Adjacent to the Big Island area is an area referred to as the Milan Bottoms, which contains isolated floodplain lakes and remnant oak – hickory stands on a series of alluvial ridges parallel to the main channel.  This area has been targeted for restoration under the Corps WRDA Section 1135 Program, and work has begun to restore historic hydrologic conditions. 

This pool’s major features are the island set running from Hog Island, suberged by Dam 16 upstream to river mile 461.2, Andalusia Island complex running ustream from approximate river mile 463.7 to 472.8.


1. Fine sediments are accumulating at accelerated rats within backwaters and other floodplain sits due to high suspended sediment concentrations and the reduced sediments transport capability of the navigation project.  High turbidity prevents colonization of aquatic plants.  An example of this may be found at the lower tip of Arsenal Island.  This site contains a backwater area that provides valuable walleye prespawn habitat under high flows.  Sediment accretion within this backwater has reduced depths to the point that late winter/spring flows are not always sufficient to ensure the accessibility of this site prior to the spawn.

2. Submergent aquatic vegetation has disappeared throughout the pool, although lotus and arrowhead have rebounded from the flood of 1993.  Grazing, biomechanical disturbance, and water level fluctuation are suspected to be primary limiting factors, and limit the ability to maintain habitats critical to migratory birds must be maintained, especially aquatic food resources and woodlands.  Examples of this may be found throughout the Pool.

3. Nuisance aquatic species such as grass carp, bighead carp, zebra mussels, and Erasian milfoil are present.  In addition, Reed’s canary grass and purple loosestrife are present and could become dominant in the absence of active control or eradication. 

4. Coarse sediments, or bed load sediments, accumulate in side channels where they fill valuable habitats and restrict flows.  The upper end of Andalusia Slough provides the most significant example of this.

5. A permanently elevated water table favors moisture tolerant forest species, limits species diversity, and may affect long-term forest health.  This is evidenced in the mid-to-lower Pool where eroded and wind-thrown trees along the river bank demonstrate a maximum root zone of about 12 to 24 inches.

6. Industrial discharges into Pool 16 contribute to water quality and habitat problems which impact natural resources.  Sylvan Slough mussel habitat may be influenced by oil seepage from adjacent industrial area and hazardous material seepasge from a disposal site on Arsenal Island.  These effects are unquantified as habitat metrics at this time.

7. The current status of Pool 16 mussel community is unknown below Sylvan Slough.  Information is needed to better assess and manage Pool 16 mussel populations.

8. The current water management regime, especially the avoidace of seasonal low water, removes much potential for periodic regeneration of aquatic habitats.  Also, rapid water level fluctuations affect livfe history cycles of fish throughout the year, but particularly during the spawning season. 

9. Development pressures from industry (fleeting) and illegal ATV use is increasing.

Resource Opportunities:

1. Restoring the full range of bottom contours and depths within the backwaters will address Resource Problem #1.  The river’s natural energy may be harnessed at select sites with features designed to (a) scour sediment, (b) maintain sediments in suspension to preven accumulation, or (c) direct sediment laden flows. At sites protected from accelerated accumulation but where natural processes cannot restore desired bathymetry, dredging can replace natural cutting and scour.  Watershed management with best management practices can limit soil loss, stream turbidity, and rates of sediment accumulation.

2. Pool management which effectively maintains emergent and submersed aquatic vegetation and forests will insure availability of habitats critical to migratory birds (Resource Problem #2).  Vegetation provides direct habitat benefits and positively influences other important resources, such as aquatic macroinvertebrates and fishes.  Opportunities to restore or maintain aquatic vegetation include: (a) island maintenance or development to shelter aquatic areas, (b) water level management, especially to provide periodic low elevations, (c) actions within watersheds and the pool to lower turbidity and sedimentation rates, and (d) maintain critical backwater habitat units at select locations, such as the Andalusia Habitat Rehabilitation and Enhancement Project (HREP) area.  Opportunities to maintain forest communities are discussed in item 4, below.

3. Design and construction of projects to utilize the river’s hydraulic energy to open or maintain side channels can be accomplished to mitigate Resource Problem #3.  Opportunities include (a) erosion protection of key side channel shorelines, (b) experimental structures designed to alter flow and increase bathymetric diversity within side channels, (c) flow regulation into degraded side channels and (d) development of bathymetric and sediment transport models for Pool 16 to aid analysis and project design.  Dredging can also restore side channel productivity, and is especially appropriate when used in combination with techniques which sustain the desired condition

4. Mitigating the long-term impacts of an elevated water table can help improve forest regeneration and tree species diversity at select sites (Resource Problem #4).  Opportunities include (a) raising ground surface elevation, (b) use of intensive regeneration aids, (c) careful management of existing diverse stands, and floodplain edge sites, (d) experimental plots testing a variety of forest management techniques, and (e) examination of pool water management profiles and topography to identify sites with best potential for diverse forest management

5. Watershed related water quality issues are addressed by several authorities, but river managers can influence effectiveness of local programs (Resource Problem #5).  Opportunities to improve watershed impacts can include (a) collaborative efforts to reduce upland soil erosion, (b) improvements to lower tributary characters including bank erosion of coarse sediments, (c) supporting efforts to solve specific water quality problems, such as high concentrations of ammonia in important habitats, and (c) initiation of needed monitoring if information is not available

6. Appropriate operation changes at Locks and Dams 15 and 16 or their structures can improve fish passage (Resource Problem #6).  Opportunities include the design and construction of fish ladders or amending lock or dam operations

7. A mussel population and habitat inventory can provide needed and basic information on Pool 16 mussels (Resource Problem #7).  Opportunities include (a) collaborative inventories involving all agencies, (b) a contracted study funded by an applicable authority and (c) development of best management guide for priority sites

8. Timely water level fluctuation, planned within the constraints of the navigation system, can induce biological responses which rejuvenate aquatic habitats (Resource Problem #8).  Opportunities include periodic reduced summer water elevation designed to mimic natural summer low flow events.  Backwater areas in Pool 16 from the mid-Pool to the dam would benefit from periodic drying and sediment consolidation.  Pursue additional authority to operate the dam as a control point.  Corps staff indicates that the Pool is regulated as a dam control point until flows exceed 75,000 cfs.

9. Expand riparian buffer along Fourth Slough in Drury L&DD, and introduce flow to Fourth Slough ton improve water quality during winter and summer.

Proposed Actions:

To facilitate planning and illustration, proposed projects are organized within geographical units.  Geographical unit boundaries and the sites of Proposed Projects within Pool 16 may be located on the Desired Future Habitat Condition maps, which follow this section.

Upper Pool 16:

Monitor habitat, flow and bathymetric characters in Sylvan Slough and select management objectives to maintain selected features.  In the main channel construction or modification of various training structurews will be used to maintain or improve fishery value.

Expand fish passage opportunity through Lock and Dam 15.  The Arsenal Power Dam and the MidAmerican power dam.

Milan Bottoms:

Complete the 1135 project.

Monitor habitat, flow and bathymetric characters within Blanchard Chute and establish a management objective of no deterioration of select characters.  Construction or modification of various training structures will be used to maintain or improve select characters.

Swift Slough Complex:

Monitor habitat, flow and bathymetric characters within Swift Slough and Jungle Run to determine need for construction or modification of various training structures will be used to maintain or improve select characters.

Restore over-wintering, backwater habitat for centrarchids with excavation within Turtle Pond

Restore moist soil and shallow aquatic vegetation communities with excavation of shallow ephemeral pools on selected islands.

Raise ground elevation on selected sites.  Utilizing fine sediments removed for over-wintering habitat or wetland restoration.  Plant sites to appropriate forest.

Smith’s Island and Andalusia Island Complex:

Investigate seasonal flow regimes to reduce sediment input to Patterson Lake Complex

Restore over-wintering habitat for contrarchids throughout backwaters.

Improve site index for mixed bottomland trees by raising ground elevation with material removed to restore fish over-wintering habitat.

Dead Slough and Andalusia HREP Area:

Monitor habitat, flow and bathymetric characters within Sisco Chute and establish a management objective to maintain mussel bed.  Construction or modification of various training structures will be objective to maintain mussel bed.  Construction or modification of various training structures will be used to maintain or improve select characters.

Restore moist soil and shallow aquatic communities with excavation of shallow ephemeral pools.

Restore fish over-wintering site within adjacent backwaters

Reduce sediment accumulation in backwater areas by diverting high flows with deflection berm constructed with shallow slopes to withstand erosion.

Monitor HREP project features and maintain as necessary to meet habitat objectives

Geneva Island Complex & Wyoming Slough:

Reduce sediment accumulation where feasible with innovative training structure design.

Diversify the forest community by planting the deflection berm and other elevated sites to mixed bottomland trees.

Restore moist soil and shallow aquatic communities with excavation of shallow ephemeral pools

Restore fish over-wintering site within island backwater.

Offer landowners natural resource management options, including incentives, easements, technical assistance or acquisition, to restore floodplain habitat characters.

Utilize any opportunities for floodplain habitat restoration to restore or simulate natural hydrologic characters of large floodplain rivers.  Emphasize restoration or simulation of characters consistent with wet prairie, moist soil, or shallow aquatic communities. 

Monitro Wyoming Slough to maintain existing values.

Pool 16 Entire:

Complete bank stabilization or flow modifications at sites where rapid bank line erosion threatens pool diversity.  The project should begin with a pool-wide inventory.

Review Pool 16 water management and determine feasibility, impacts and anticipated results of potential changes in water management, especially the partial restoration of seasonal low water elevations. 

Inventory and assess mussel populations throughout the pool and design appropriate habitat management.

Pool 16 Watershed:

Use existing programs and incentives offered by federal, state, and county agencies and private groups to reduce the contribution of sediment from tributaries.

Request appropriate water quality authorities for assessment of urban and industrial discharges.  Develop cooperative programs to resolve any problems for river resources.

Upper Mississippi River System:

Develop pool-wide environmental planning aids, including hydraulic models, topographic and bathymetric surveys, substrate maps and other information needed to facilitate engineered and science based solutions for habitat diversity.

Design, construct and test structures to maintain or restore desired habitat features. 

Expected or Desired Results:

1. A combination of engineered and science based solutions will aid in the restoration and maintenance of important habitat features of side channels and backwaters at select sites.  Sediment accumulation attributed to the navigation project can be reduced at project sites to maintain or restore important habitat values.  Aquatic values and the life span of targeted backwaters will be extended.  Fish over-wintering habitats will be maintained within five mile intervals.  Side channels targeted for improved management of coarse sediments may be maintained indefinitely.  Main channel training structures, however, will preclude much potential for large-scale regeneration of aquatic habitats, and the long-term trend to a less diverse system will continue. 

2. Habitats critical to migratory birds, especially aquatic food resources and forests, will be improved and extended if the problems of suspended sediments and sustained high water elevations can be mitigated. Water management alternatives, even in small scale, promise important, periodic rejuvenation of aquatic vegetation. 

3. Expected or desired results related to sediment problems within side channels are included in number l above.

4. Naturally sustained diverse forest communities can be developed on sites raised significantly above the water table or maintained on higher areas of the floodplain edge.  Careful management and intensive regeneration efforts will maintain desirable communities on some existing sites.  Sediment accumulation will slowly improve the woodland site index at some locations.  There will be opportunities for forest restoration on lands currently in agricultural production within levee and drainage districts.  Forest stand improvement goals will be established throughout the Pool. 

5. Long-term improvement in watershed management is expected to reduce sediment loads from immediate watersheds and the basin. River managers must ensure that river impacts are a measured cost of upland erosion and that Mississippi River natural resource and water quality issues are represented in planning and implementation of watershed management.  Programs which benefit restoration of tributary floodplains as the Wetland and Conservation Reserve Programs or the Emergency Wetland Program will be identified and supported. 

6. The installation of fish passage structures or amended operation may improve the opportunity for fish movement between pools.

7. Mussel population and habitat monitoring will be maintained and best management guidelines will be established and implemented. 

8. Expanding the vertical dimension of water level fluctuation via periodic summer drawdown will promote productivity of aquatic habitats and improve fish and wildlife habitats and populations.  A minimum 10 year drawdown cycle will be implemented. 

Back to FWIC Upper Mississippi River Pool Plans


Last updated: May 12, 2009