Maryanne Reiter, hydrologist at Weyerhaeuser on “Spatial and temporal turbidity patterns over 30 years in a managed forest of Western Washington”:

“In the early 1980s there was concern over sediment filling Capitol Lake.”  Weyerhaeuser wanted to determine if forest practices were contributed, so created a watershed plan.  

Study started in 1974.  Several 1 square mile sections studied, plus multiple grab sites. 

Used turbidity as a measure since more data was available than suspended sediment on.  A correlation between the two was demonstrated.

The measures of turbidity was adjusted for flow.  The watersheds, although near, behaved differently, and account.  

Harvest does not account for the decrease. Changes in way roads were constructed, sediment traps and ditching are likely influential.

Underlying geology was considered.  There was a marked difference between glacial and volcanic terrains.

New sampling equipment were installed in 2006. 

“This study has shown decreasing trends in winter turbidity for at the small and large watershed scale.” 

Conclusion:  Decline largely due to improvements in road construction and maintenance practice.

Questions and answers:

Was there a problem with clogging culverts with vegetation?

No, design includes settling basin to allow cleaning.

Questions regarding road construction.

Most of the road consruction had been completed prior to sampling.  Traffic more than density of roads.