Influence of spur dike submergence on local scour and flow structure under ice cover

This study investigates the combined effects of spur-dike submergence and ice cover on local scour, deposition ridge development, and flow structure in ice-affected channels. Laboratory experiments were conducted in a large outdoor flume to quantify the influence of spur-dike submergence ratio ( S = h 1 /h , where h 1 is the water depth above the spur-dike crest and h is the approach flow depth), median sediment size ( d 50 ), spur-dike alignment angle relative to the main flow direction ( θ ), and the ratio of Manning roughness coefficients of the ice cover to the bed ( n ᵢ/ n b ). Clear-water scour depth ( d s ) and downstream deposition ridge height ( h r ) were normalized by h to enable consistent inter-case comparison. Results show that increasing submergence systematically weakens near-bed circulation, leading to proportional reductions in both maximum normalized scour depth and deposition ridge amplitude, with overall decreases of 75% and 60%, respectively, as S increases from 0 to 0.4. Rough ice cover intensifies near-bed turbulent kinetic energy (TKE), shifting turbulence toward the bed and producing deeper scour and more pronounced deposition ridges than smooth-ice and open-channel conditions. The 90° spur-dike alignment consistently yields the largest scour depths under both open and ice-covered flows, reflecting enhanced nose-attached downflow and secondary circulation. Based on dimensional analysis and regression of the experimental dataset, empirical equations incorporating S , θ , d 50 , and n ᵢ/ n b are proposed to predict normalized maximum scour extent, demonstrating good agreement with measurements and providing a practical framework for estimating spur-dike-induced morphological responses in ice-affected rivers.