Plum Creek Sediment Budget Study

Soil sample being collected from eroded streambank.

Plum Creek is part of the Total Maximum Daily Load (TMDL) and watershed management plan for total phosphorus (TP) and total suspended solids (TSS) in the Lower Fox River Basin. Initial streambank inventories of the Plum Creek conducted in 2014 by Outagamie County Land Conservation Department revealed moderate to very severe streambank erosion occurring along the main stem of Plum Creek and its tributaries. Initial estimates indicate that streambank erosion may be contributing up to 45 percent of the annual sediment load in the stream. Not enough information was available at the time of the TMDL analysis to separately model streambanks; therefore the land area was lumped into the agriculture land use for modeling. If stream processes in the watershed are producing almost half the sediment load, the proposed TMDL goal to reduce sediment loads by 74.6% from agricultural land will not be achievable through upland soil conservation practices alone. Preliminary inventory results prompted the need for a stream corridor-based sediment budget and source apportionment study to better quantify the proportion of TP and TSS loading from in-stream sources of bank and channel erosion compared to upland soil erosion.

In the fall of 2016, the United States Geological Survey (USGS) Wisconsin Water Science Center with assistance from Outagamie County Land Conservation Department began a watershed assessment of the stream channel process and sediment sources in the Plum Creek watershed. The goal of the study is to understand how different sources of sediment and phosphorus from soil erosion, gullying, and streambank erosion are transported and stored in Plum Creek. Two in- situ suspended sediment samplers were installed on Plum Creek where monthly samples will be collected for one year. Soil samples were collected from a variety of land uses including row crops, woods, road ditches, eroding ravines/gullies, stream banks, and stream beds. Rapid geomorphic assessments of stream channel characteristics were also performed on 30 different sites on the Plum Creek and its tributaries. Soil sampling and rapid geomorphic assessments were completed in June of 2017. Soil samples that were collected will be analyzed for total phosphorus, particle size, density, loss on ignition, and trace elements used in sediment fingerprinting. A sediment budget and maps of the sources and sinks of sediment and total phosphorus are expected to be completed in 2018. Results of the study will be submitted to a journal and will be used to guide TMDL implementation efforts in the Plum Creek watershed.