A. Drainage and topography shall be a primary consideration of any subdivision.
B. The preservation of natural flood areas, streams, washes, arroyos, rivers or ephemeral drainage courses should be maintained, if possible, in their natural state. The limits of the ten (10) year flood event shall define the extent of the area of concern. The only exceptions are for roadway crossings and utility lines, if no other alternative exists. Subdividers are encouraged to preserve natural flood areas to the maximum extent possible.
C. Drainage layout and development shall meet all State and Federal requirements to allow residents of Chino Valley to purchase flood insurance, to receive disaster relief, to obtain real estate loans and to minimize flood damage.
D. Subdivision improvements that propose grading and/or grade changes shall not have an adverse impact on surrounding property. At the boundaries of the subdivision, all drainage and floodwaters shall be accepted and released so that the flow characteristics are minimally disturbed by providing appropriate entrance and exit transitions.
E. All weather access to all lots shall be provided during the regulatory flood, which means depths of flows over streets will not exceed one (1) foot to allow passage of emergency vehicles. The standard applies to both public and private streets.
F. All drainage ways that convey fifty (50) cubic feet per second or more during a one-hundred (100)-year flood event, shall be considered regulatory flood ways. Regulatory flood ways shall be maintained by the adjacent property owner within the subdivision, unless the Town has agreed to allow such flood ways to be dedicated to the Town with provisions for maintenance access ramps. Flows less than fifty (50) cubic feet per second shall be regulated for impacts to buildings and structures, particularly, the placement of the finished first floor or basement, and areas designated for containing such flows shall be identified as a common area or noted on the final plat as impacting a lot and the lot owner's responsibility for maintenance.
G. Drainage basins or watersheds with known flood hazards shall be designated as critical basins. Within designated critical basins, all proposed subdivisions shall address on-site detention for the two (2)-, ten (10)- and one hundred (100)-year flood events to mitigate the post-development drainage to the pre-development levels. If the subdivider can demonstrate that on-site detention will exacerbate the downstream condition then the Public Works Director may allow for modifications to the requirement.
H. A drainage study that addresses the hydrologic and hydraulic components relating to onsite and off-site drainage shall be developed for each subdivision. The study shall be prepared by a registered Arizona Professional Engineer. The drainage study shall be approved before the street improvement plans and final plat are approved. If the subdivision will be developed in phases, a master drainage plan will be required.