Walnut Creek IA 05-NSH-1450

from confluence with unnamed tributary at the S30/31 line in T73N R38W Montgomery Co. to confluence with unnamed tributary in S3 T76N R38W Pottawattamie Co.

Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2012 - 2014
Stream/River Water Quality Data	CY 2012 - 2014
Lake Water Quality Data	CY 2010 - 2014
Biological Sampling Data	CY 2010 - 2014*
Fish Kill Data	CY 2010 - 2014
Fish Tissue Sampling Data	CY 2010 - 2014
Continuous Dissolved Oxygen Sampling Data	CY 2010 - 2014
*Biological sites sampled in both 2009 and 2013 were also assessed.

Open Segment Map
View assessment methodology in new window

Cycle: 2016
Release Status: Final
Overall IR: 3 - Insufficient data exist to determine whether any designated uses are met.
Trend: Unknown
Created: 9/23/2016 6:52:08 AM
Updated: 9/23/2016 7:03:54 AM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Assessed

Class BWW2

Aquatic Life - Warm Water Type 2

Not Assessed

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 (primary contact recreation) uses remain "not assessed" (IR 3a) due to the lack of information upon which to base an assessment. Due to the age of information upon which the previous assessment was based, the Class B(WW2) aquatic life uses are now considered “not assessed” (IR 3a).

Assessment Explanation

Assessment historically based on 1998 IDNR Fisheries data (see below). Assessment was changed to "not assessed" for the 2012 IR cycle due to age of biological data (>10 years).

[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

Due to the age of information upon which the previous assessment was based, the Class B(WW2) aquatic life uses are now considered “not assessed” (IR Category 3a). Previous assessments “fully supporting/evaluated” were based on biological data collected in 1998 as part of an IDNR Fisheries stream sampling project: Manchester research station. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data. The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1998 evaluated FIBI was 28 (fair). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 31 and this site passed the BIC with the use of the uncertainty adjustment value (UAV) of 7 points applied to single sample assessments.

Because the 1998 biological data are now well over 10 years old, the 2010 assessment of the Class B(WW2) aquatic life uses is changed from “fully supporting” to “not assessed”. As water quality data age, they are less able to represent current water quality conditions. As data age beyond ten years, their ability to represent current water quality conditions is increasing suspect. Additional monitoring is needed in this assessment segment to update status of its aquatic communities.

Monitoring and Methods

Assessment Key Dates

None listed

Methods

150

Monitoring data more than 5 years old