I dont pretend to have all the answers but sustainable development is good sense not rocket science. First, dont build over green land in the green belt - either redevelop Ashton Gate or find a suitable brownfield site near existing good transport links. Second, seriously consider sharing any new ground. Thirdly use well established green design principles eg the One Planet Living Principles that are outlined here:http://www.oneplanetvision.org/one-planet-living/opl-framework/
I took part in the BCFC consultation and submitted some ideas on green stadium design plus examples of several football clubs who have used green design principles (see here and Dartford FCs Princes Park stadium design, pictured). Despite asking for a response by email and phone call I received none. Had city gone for a top notch green stadium design it would have been much harder for people like me to oppose it - and perhaps it would have been harder for Ashton Vale people too. Shouldn't our aspiring 'green capital' have a green football stadium??