Sentence:  The apparent success of the City and South London triggered an <WSD>avalanche</WSD> of bills for Tube railways, and in 1892 a Joint Select Committee of Parliament set out some ground rules. 
Meaning of the word marked with <WSD> tags:  A sudden, great, or irresistible descent or influx; anything like an avalanche in suddenness and overwhelming quantity; a barrage, blitz, etc.