Grading Plans: General Info

This Site is maintained by Del Rio Engineering,
civil and hydrology engineers in Phoenix, Arizona. We provide civil engineering services throughout Arizona, including grading and drainage plans for projects from large commercial sites, subdivisions or individual home and lot owners.
Many municipalities and jurisdictions have areas susceptible to flooding from precipitation and/or runoff. Agencies such as FEMA (Federal Emergency Management Administration) and county flood control districts have studied and identified floodplain areas and provide this information to the public.
Flooding risk is expressed in terms of 100 year storms. (1 chance of a storm of that magnitude every 100 years). FEMA maintains a floodplain database using data provided by local agencies and other sources. Civil engineers use this information to ensure that construction is built with consideration for flooding and runoff issues. Civil engineers also analyze local topography to predict how a storm will affect a building site and how proposed construction will affect local runoff and drainage. This ensures that new construction does adversely impact neighbors, both upstream and downstream.
FEMA maps (very hi-res & slow)
Maricopa County- Flood Control
FEMA maps
The two main flooding dangers are being in the way of runoff or being in a ponding area. A ponding area fills up with stormwater due to some barrier, either natural or man-made, that blocks water flow. Berms, levees, block walls, roads, buildings, railroads and elevated canals and aqueducts are frequent causes of ponding.
Many states and municipalities require grading and drainage plans for new construction and for modifications to existing structures. Grading and drainage plans are almost always required for commercial construction and are often required for a single family home site. In Maricopa County, Arizona, a grading plan is required for new custom homes on lots of 1/2 acre or more. Grading plans are also required for fences and outbuildings.