▁appears ▁as ▁a ▁sudden ▁increase ▁in ▁the ▁water ▁level . ▁A ▁tid al ▁bore ▁takes ▁place ▁during ▁the ▁flo od ▁t ide ▁and ▁never ▁during ▁the ▁e bb ▁t ide . ▁ ▁A ▁tid al ▁bore ▁may ▁take ▁on ▁various ▁forms , ▁r anging ▁from ▁a ▁single ▁breaking ▁wave front ▁with ▁a ▁roll er ▁– ▁somewhat ▁like ▁a ▁hyd ra ul ic ▁jump ▁– ▁to ▁und ular ▁b ores , ▁compr ising ▁a ▁smooth ▁wave front ▁followed ▁by ▁a ▁train ▁of ▁secondary ▁waves ▁known ▁as ▁wh el ps . ▁Lar ge ▁b ores ▁can ▁be ▁particularly ▁unsafe ▁for ▁sh ipping ▁but ▁also ▁present ▁opportun ities ▁for ▁river ▁sur f ing . ▁ ▁Two ▁key ▁features ▁of ▁a ▁tid al ▁bore ▁are ▁the ▁inten se ▁tur bul ence ▁and ▁tur bul ent ▁mixing ▁generated ▁during ▁the ▁bore ▁propag ation , ▁as ▁well ▁as ▁its ▁r umb ling ▁noise . ▁The ▁visual ▁observations ▁of ▁tid al ▁b ores ▁highlight ▁the ▁tur bul ent ▁nature ▁of ▁the ▁sur ging ▁waters . ▁The ▁tid al ▁bore ▁indu ces ▁a ▁strong ▁tur bul ent ▁mixing ▁in ▁the ▁est u ar ine ▁zone , ▁and ▁the ▁effects ▁may ▁be ▁felt ▁along ▁considerable ▁distances . ▁The ▁velocity ▁observations ▁indicate ▁a ▁rapid ▁dec eler ation ▁of ▁the ▁flow ▁associated ▁with ▁the ▁passage ▁of ▁the ▁bore ▁as ▁well ▁as ▁large ▁velocity ▁fl uct u ations . ▁A ▁tid al ▁bore ▁creates ▁a ▁powerful ▁ro ar ▁that ▁comb ines ▁the ▁sounds ▁caused ▁by ▁the ▁tur bul ence ▁in ▁the ▁bore ▁front ▁and ▁wh