His research started with studies of the hydrology of the River Clyde that expanded to a range of subjects including, flood risk, dredging, nuclear waste management, decommissioning of North Sea platforms and contaminated land.
Fleming was involved in the planning stages of the Glasgow Garden Festival of 1988 and established a way of reusing dredgings from the Clyde to provide topsoil for the event.
He has served as a non-executive director of British Waterways, Port of Tyne boards and for WRAP, a government quango whose aim was to promote recycling and resource efficiency.
His PhD investigated the movements of water and sediment in the Clyde system using digital simulation software he helped pioneer at Stanford.
[7] He was later asked by deputy prime minister John Prescott to chair a commission into the effects of the flooding, which resulted in a report entitled "Learning to Live with Rivers".
[10] Fleming co- founded and served as chairman of the charity Engineers Against Poverty in 2000 and later the Association of Environmental and Ecological Clerks of Works from its formation until January 2018.
His academic work had shown that dredgings from the River Clyde contained valuable nutrients washed down from upstream agricultural land and, once treated to remove heavy metals, could be re-used as opposed to being discarded as previous.
Fleming generated topsoil for the garden festival this way and subsequently licensed the technology used to a company that sold the material under the brand name ClydeSoil.
As consultant to the UN/ FAO, he worked extensively in land management in Morocco to coastal erosion and introduced computer modelling in hydrology to the UN.
During an extended period he acted as Visiting Professor to the Facoltà di Agraria at Padova University, establishing computer simulation of flow and snow melt prediction models in the Italian Alps[13] during 1982–1987.
The company, of which Fleming is currently the chairman, now works across many sectors including energy, harbours, roads, housing, nuclear waste, ecology, noise, decommissioning concrete gravity platforms, and coastal erosion of golf courses[5] including Trump Aberdeen, North Berwick, Royal Aberdeen and Muirfield.
Fleming has been Peer Review Consultant on the Low Level Waste Rebository (LLWR) at Drigg since 2008 and on the decommissioning of the Dunlin Alpha oil platform in the North Sea.