Comparison of Different Techniques to Assess Surface and Subsurface Streambed Colmation with Fine Sediments

Methods commonly used to assess physical colmation are mainly based on observations of streambed surface. These methods have been widely used but remain relatively subjective because of the observer effect. Visual estimation, penetrometry, hydraulic conductivity and wooden stake methods were applied to assess colmation conditions on 9 reaches with the objective of comparing them with the direct measurement of fine sediment content in subsurface habitat using the freeze coring method. The results demonstrated that surface estimation efficiency in separating colmation level is relatively poor and cannot indicate the colmation pattern of the subsurface zone and thus could not be a good indicator of internal colmation. Among the different techniques used to estimate subsurface colmation, wooden stakes and penetrometry have presented inconstant results in assessing internal colmation. A high correlation between percentage of fine sediments from freeze coring and hydraulic conductivity (R-2 = 0.98) was found. Hydraulic conductivity was therefore identified as the most accurate and robust method. Thus, this method could be proposed for large scale and long term colmation monitoring programs.