Louisville Bend IA 06-WEM-1729

Assessment Comments

Assessment remains based on (1) information from the IDNR Wildlife Bureau and (2) results of watershed modeling by the IDNR Water Quality Bureau.

Basis for Assessment

SUMMARY:  The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supported”.   This assessment remains based on (1) information from the IDNR Wildlife Bureau and (2) results of watershed modeling conducted in 2002 by the IDNR Water Quality Bureau.   The fish consumption uses remain "not assessed" due to the lack of water quality information upon which to base an assessment.   Due only to a change in IDNR's assessment/listing methodology, the 2004 assessment of the Class B(LW) aquatic life uses ["fully supporting / threatened" (minor impacts)] is changed to "fully supporting".   Other than this change in methodology, this new (2006) assessment is the same as that developed for the previous (2004) assessment/listing cycle (not impaired) and does not reflect any known change in water quality.

EXPLANATION:  The aquatic life uses are assessed as "fully supported" based on information from the Iowa DNR Wildlife Bureau and on results of watershed modeling conducted in 2002 by the IDNR Water Quality Bureau.   At the recommendation of U.S.  EPA Region 7, IDNR's 2006 assessment/listing methodology was changed to eliminate use of the "fully supported/threatened" (not impaired) category.   Thus, previous assessments identified as "fully supported/threatened" (not impaired) were changed to "fully supported" for the 2006 assessment/listing cycle.   This change does not alter the 2004 assessment:  this waterbody remains in IR Category 2a.   The 2004 assessment is included below:

The aquatic life uses are assessed as "fully supporting / threatened."  The upgrade in support of the aquatic life uses from "not supporting" (see assessments for previous Section 305(b) reporting cycles) to "fully supported / threatened" is based on the following information from the Iowa DNR Wildlife and Water Quality bureaus.   The chute at Louisville Bend was originally closed in conjunction with the Missouri River Bank Stabilization and Navigation Project.   Construction during the project used dikes and revetments to cut off the side channel across bend in the Missouri River.   These activities resulted in siltation impacts at this wetland.   The main project elements for the mitigation at this site is re-establishing the open water and floodplain habitat at this site.   In order to reconnect the land with the river, controlled openings were constructed at the inlet and outlet of the closed chute.   Because the constructed side channel is at a higher elevation than the adjacent river, a pump was also installed at the inlet to pump in water during periods of low river flows.   Water in the constructed chute is maintained by the regulating outlet.   Restoration of this area was completed in 1995.   The site continues to function as planned providing 270 acres of valuable shallow water fish and waterfowl habitat.   Watershed modeling on this wetland indicates that sediment delivery to the wetland is very low.   DNR Wildlife Biologist indicates that the Missouri River does not breach the original high bank, but occasionally (10-15 years) flood waters do enter the wetlands directly adjacent to the river.   However, it is not thought that the resulting deposition is significant.   Because the impacts from siltation and hydrologic modification of the Missouri River have been adequately mitigated, the level of support of the aquatic life uses is upgraded from "not supported" to "fully supporting / threatened."  The assessment category for this wetland is "evaluated."  In terms of Section 305(b) reporting, "monitored assessments" are based primarily on recent, site-specific ambient monitoring data and thus have relatively high confidence.   "Evaluated assessments" are those based on data older than five years or other than site-specific ambient monitoring data (e.g., desktop models or questionnaire surveys of fish and game biologists [=best professional judgement]) and thus have relatively lower confidence.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this wetland.   In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.