Development and Stormwater Runoff in the Upper Agua Fria Watershed

Article by: Tony Angueira, Yavapai County Flood Control District

The Upper Agua Fria River Watershed encompasses an area of over 1400 square miles and nearly 6,400 feet in elevation change.  The landscape ranges from pine forests, to mixed chaparral, to grasslands and rocky desert.  The Agua Fria River is fed by a dendritic network of (mostly) ephemeral streams and washes.  In predevelopment times, the river could vary from its trickling minimum to its raging, stormwater-fed peak flow with little potential for impact to human life and property.

Today however, the banks of Agua Fria River are far more developed.  This encroachment of irresponsible riverside development often results in catastrophic peak flows that seriously impact downstream communities like Black Canyon City with flooding and pollution.  The watershed is slow to rebound due to impervious roads and buildings that alter flows and lessen the absorption of water down into the ground.

Proper planning and building on high ground, above the boundary of the 100-year flood plain is now more crucial than ever.  Storms are increasing in intensity, which leads to a greater likelihood of flash floods as sudden, heavy rains tend to roll over the surface, rather than soak into the ground.  Detention ponds that hold rainwater, terraced development and thoughtful planting of shrubs and grasses can both lessen flood impacts and provide water for plants longer into drought season.

It is important to understand the potential effects of unmanaged stormwater runoff.  It washes silt, sediment, oils and other chemicals, and trash from upstream areas and roads, down into streams and the communities that lie in the flood plain.  Natural flooding events will happen and should be planned for.  Building resilient communities is key to the survivability of such events.  While we cannot turn back the clock on existing developments, when it comes to floods, we must always think about ways to improve our Agua Fria riverside community resiliency.