Questions About the Silver Stream's Concrete Lining

• At what rate does the concrete lining erode? 
• Has it been replaced fully or partially over the course of the steam's existence?
• What other streams provide examples for the performance of concrete linings over time?
• What kind of concrete was used? What are its main components?
• In what areas is the erosion greatest?
• What are the environmental concerns with using concrete stream linings, if any?
• Is it possible to distinguish the elemental compounds present in the steam's sediment that come from the concrete vs. other sources?