Technical Report No. 5

SUSPENDED SEDIMENTS IN JOE LEARY SLOUGH, A NORTH PUGET SOUND COASTAL STREAM DRAINING AN AGRICULTURAL WATERSHED

Douglas A. Bulthuis

April 1996

Bibliographic Citation
Bulthuis, Douglas A. 1996. Suspended sediments in Joe Leary Slough, a North Puget Sound coastal stream draining an agricultural watershed. Washington State Department of Ecology, Padilla Bay National Estuarine Research Reserve Technical Report No. 5, Mount Vernon. Washington. 46 pp.

Abstract
The concentration of suspended sediments was measured weekly for one year at three locations in Joe Leary Slough and hourly for 26 hours on four occasions to indicate the seasonal and tidal variations. Water flow in Joe Leary Slough was influenced by the tide. The concentration of suspended sediment was highest during falling tides when outward flow was greatest. Suspended sediment concentration varied five to ten fold during the tidal cycle. Seasonally, the concentrations during winter were about four times as high as the dry season mean of about 20 mg l-l. Peak concentrations during high rainfall and flooding were up to 200 mg l-l. Joe Leary Slough contributes about 50-100 metric tonnes of sediment to Padilla Bay each year. The presence of cover crops on fields during winter decreased the flow of suspended sediments from the fields to the slough. The higher concentration of suspended sediments in Joe Leary Slough during winter reinforces the importance of winter cover crops in protecting water quality in fresh water sloughs and the bays to which they drain.