The City of Madison Engineering Division often receives questions from the public about how land may be developed in the future, and how it intersects with stormwater goals. City of Madison Engineering staff compiled commonly asked questions with answers:

Question: The flood mapping shows existing flooding on the field I was going to sell to be developed. What does that mean?

Answer: The flooding rasters (colored mapping) show how our computer models predict the way water currently behaves during various storm run-off events and the colors indicate the associated depths of the water.  If there is generally standing water on lands that would indicate there is existing unintended detention occurring.  That unintended detention would likely need to be accounted for by those wishing to develop the property.  Sometimes mapping will show areas of concentrated flow, which may indicate the need for the water to be conveyed by pipes or an open channel when the property develops.

Question: The flooding on my property is caused by the choice of culvert that the County/Town put under the road downstream of my property.  They should upgrade the culvert and my property will be flood free. 

Answer: Upgrading an existing culvert could be a potential solution to upstream flooding, however care must be taken to make sure other properties are not flooded because of a change in the stormwater drainage patterns. The City does not have jurisdiction over the County or Towns and how they have determined the infrastructure needs in the past or currently, although we do try to coordinate our efforts when possible. Our models however can be used as a tool for the future to ensure making one change in a location doesn’t inadvertently cause an issue elsewhere.

Question: Does the storage that the flood mapping shows I am providing count toward my detention requirements under the City’s Stormwater Code right now? or in the future? 

Answer: If there is no proposed change in use or zoning to the property nothing needs to happen to bring the property into compliance with the City’s Stormwater Code.  However once there is a change to the property’s use or a subdivision of the property, then the City’s ordinance requirements will have to be met.  If a property currently has “unintended detention”, the Stormwater Code describes how to calculate the storage that occurs in the property’s current / unaltered condition before it develops and how to calculate the storage necessary to meet the stormwater requirements as part of the development. The short answer is that unintended detention needs to be accounted for upon development and the additional storage requirements to address the increase in runoff associated with the development will get added to that amount.  A Civil Engineering firm would be able to calculate the detention requirements based on land use, topography, soil types, etc.

Question: Can I have an engineer complete an analysis for me for comparison to your work?  

Answer: Yes, our models are available for use by engineering companies to assist with design considerations. A request should be made to the City Engineer. These computer programs run in XP SWMM or PC SWMM so any consultant wishing to utilize these computer files must have appropriate training and software.

Question: Will the model account for new development and future land use?

Answer: The model is focused on flooding problems in existing conditions and will represent the current drainage system and land use conditions. However, model results will be used to inform future development by identifying undeveloped areas that are currently prone to flood risk. It will also be used to determine storage requirements for natural storage areas in undeveloped land. An example of how the model will be used to guide future development is within the Reiner Neighborhood Development Plan that was recently completed by the City.

Question: How will the model account for future development?

As new development is proposed, the models can be used to identify areas of unintended detention, general land needs for water storage or conveyance and can be used to inform sizing of the infrastructure. The models are also useful to identify flow volumes to ensure pipes and culverts are sized appropriately. As the future development plans are designed those areas can be put into the models to understand how the entire system functions.