Evaluation of the imprint of urban channel adjustment and management

摘要

Decades of research have clarified the nature of urban channel adjustments and guided watershed management, so that now it is possible to conduct geomorphological evaluations of urban channel systems, including their management. Such evaluation may address functionality, appearance and resilience. Fountain Hills, Arizona, urbanised since 1970, offers an ideal case for evaluation. The 46 washes on which the urban area has been superimposed are in five groups, with 29% of washes currently categorised as near natural, 23% as adjusting but could recover, and 65% having some elements of the appearance of original washes. Overall, the management goal to maintain what is natural has not been realised, but an alternative objective stated as the need to achieve naturalisation is more viable. Those sections (11% of the total) which do not achieve the requirements of the guiding Ordinance include channelisation by hard engineering and sections incorporated into golf courses. Functionality is satisfactory in the 60% of wash length that has achieved naturalisation. Appearance is appropriate for that same wash length, although golf course developments produce wash lines at variance with the natural character. Short-term resilience is accommodated by the wash management programme and by ongoing adaptive management. Land ownership accounts for some of the variations encountered. This evaluation approach could be applied to other areas, with a holistic basin plan to include the possibility of geomorphological change, thus reducing the need for adaptive management as urbanisation progresses and intensifies. Now that evaluation is feasible, proactive catchment management could be employed as a basis for introducing geomorphic design.