**Examination of Blockage E**ff**ects on the Progression of Local Scour around a Circular Cylinder**

#### **Priscilla Williams, Ram Balachandar \* and Tirupati Bolisetti**

Department of Civil and Environmental Engineering, University of Windsor, Windsor, ON N9B 3P4, Canada; williamq@uwindsor.ca (P.W.); tirupati@uwindsor.ca (T.B.)

**\*** Correspondence: rambala@uwindsor.ca

Received: 30 October 2019; Accepted: 11 December 2019; Published: 13 December 2019

**Abstract:** An evaluation of scour estimation methods has indicated that the effects of blockage ratio are neglected in both scour modelling and development of new predictive methods. The role of channel blockage on the mechanism and progression of local scour is not well understood, and further analysis is required in order to incorporate this effect into scour estimation. In the present investigation, local scour experiments were carried out under varying blockage ratio. The results were compared with data from literature in order to explore the effects of blockage ratio (*D*/*b*, where *D* is the pier diameter, and *b* is the channel width) on equilibrium scour depth (*dse*/*D*, where *dse* is the depth of scour at equilibrium). It was determined that *D*/*b* had a small influence on both *dse*/*D* and the progression of scour depth (*ds*/*D*) when relative coarseness *D*/*d*50 < 100 (where *d*50 is the median diameter of sediment), and that the influence appeared to be amplified when *D*/*d*50 > 100. The efficacy of scour estimation methods used to predict the progression of local scour was also dependent on *D*/*d*50. A method of scour estimation used to predict *dse*/*D* was evaluated, and it was similarly found to be particularly effective when *D*/*d*50 < 100. In future work, further experiments and analysis in the range of *D*/*d*50 > 100 are required in order to establish the role of *D*/*b* under prototype conditions and to refine existing scour estimation methods.

**Keywords:** scour and erosion; time scale of local scour; blockage ratio
