PRELIMINARY SURVEYS AND GIS MAPS OF TOTAL SUSPENDED SOLIDS IN THE CATFISH CREEK 
WATERSHED, DUBUQUE COUNTY, IOWA

William Niemann, Daniel Call, William Knuth, Katrina Krakow, Andrew Huck, 
Christopher Green and Zachary Gustafson
Department of Natural & Applied Sciences, University of Dubuque, Dubuque, IA

The Catfish Creek watershed contains five tributary streams that merge into a 
single common stream a short distance upstream from its mouth at the Mississippi 
River in Dubuque, IA.  A study was conducted of the levels of total suspended 
solids (TSS) in each of the tributaries at several times over the past several 
years at various flow conditions.  Data for the study were obtained from: (1) 
gravimetric measurements of TSS, (2) turbidimetric measurements of stream 
turbidity, (3) IOWATER transparency tube measurements of water clarity, and (4) 
IOWATER database measurements for transparency tube measurements, as collected 
by other volunteers.  The predictive capabilities of rapid measurement 
techniques, such as turbidity and transparency tube measurements, in estimating 
TSS values were evaluated.  Turbidimeter readings in nephelometric turbidity 
units (NTUs) resulted in a higher coefficient of determination (R2) and better 
predictive capability than transparency tube readings.  This may be due to the 
greater subjectivity and more limited overall range of possible values (i.e., 0-
60 cm) inherent with the transparency tube method.  However, the transparency 
tube is less expensive, and numerous measurements from the watershed are 
available in the IOWATER database.  Data from the IOWATER database, including 
transparency tube “snapshots” of water clarity from the tributaries on specific 
weekends, were used to develop a preliminary geographic information system (GIS) 
map of the watershed regarding the presence of TSS in the five streams.  This 
type of approach, along with an account for variation in sediment levels with 
flow, may be useful in determining the particular tributaries that are in the 
greatest need of attention in reducing erosion into the watershed.

Keywords:  total suspended solids, turbidity, transparency, erosion, IOWATER