HomeMy WebLinkAboutStormwater Mapping Background1/11/12
City of Bozeman
Storm Water Mapping
Purpose:
The City of Bozeman is obligated to provide a “comprehensive map of the storm water system and
receiving waters in a reproducible and readily available [form] for use by the public, city departments,
and MS4 stakeholders”, according to a recent Municipal Separate Storm Sewer System (MS4) Audit
dated 12/12/11. The audit was commissioned by the Department of Environmental Quality as a part of
our existing Montana Pollution Discharge Elimination System (MPDES) storm water permit for lawful
discharge of City runoff into local waterways.
In addition to meeting regulatory requirements (specifically Minimum Control Measure #3), the City has
identified many needs for a complete map of the storm water system including information on the size
and condition of each control. A GIS system will allow us to efficiently manage and plan for such a
diverse utility, including the ability to accurately track any costs associated with maintaining the
infrastructure.
Background:
The City has various records depicting storm water infrastructure throughout the organization.
Information is available in the form of individual hard‐copy record drawings for each subdivision and
special improvement district. Some data is also made available on quarter‐section grid maps.
There have been at least two previous efforts in creating comprehensive digital storm water data. In
2002 the City contracted for the GPS collection of water, sewer and storm water features (fixed points
only). This project resulted in the identification of 676 manholes and 1,905 inlets. In 2004 the City
contracted for the completion of a Storm Water Master Plan (adopted 2008). Deliverables from the
plan included 1,815 pipe segments.
Considerable effort will be required to build a comprehensive map of the storm water system.
Essentially, all existing data will need to be migrated into a unified system while all existing and future
subdivision and SID record drawings must be digitized. Extensive field work will be necessary to
delineate many features. This information will then need to be maintained throughout the life of the
system.
1/11/12
Recommendation:
Section 6.8 of the 2004 Storm Water Facility Plan recommends the following “phased” approach to
developing and maintaining an accurate storm water map and GIS database:
1. Develop Database Maintenance Procedures
o I would suggest updating the Grid Maps & developing existing data needs first
2. Fully Incorporate the Grid Maps
o This will be the most time consuming task – I would estimate at least one thousand
hours of work to bring the information up‐to‐date
3. Add Open Channels
o This should be done last
4. Update Poorly Mapped Areas of the Database
o This should be done in conjunction with step #2
5. Incorporate Remaining Documentation‐Based Data
o This should be done in conjunction with step #2
The plan also recommends “The City should require that engineers or developers to submit all new storm
water infrastructure information to the City in GIS with coordinates, inverts, and elevations….”(6.7.2).
This requirement is critical to maintaining the data for future use.
There are at least two ways of completing the above tasks. The City could make progress using existing
resources and staff to construct the dataset “in‐house”. This would be similar to the method we utilized
for water and sewer infrastructure. The advantages would be a greater level of accuracy, control and
buy‐in. The disadvantage to doing the work in‐house is that it may take a substantial amount of time to
complete (four years for water & sewer). Another option might be to hire a local engineering firm for a
portion of the work. The advantage would be an expedited timeline, allowing City staff to focus on the
overall system and data development. The disadvantage of hiring a contractor will most certainly be
cost (>$180K for 2004 Facility Plan mapping).
I look forward to working with City staff to determine the best solution (likely a combination of above
two options). We have already begun the process of completing some of the work in‐house. This should
allow us to leverage any existing information as we move forward. I am confident that we can use
existing staff and resources to maintain the data in the future once the initial inventory is created.
If the City wishes to pursue creating a comprehensive storm water map using outside assistance, I
recommend that we draft a Request for Proposals outlining specific mapping needs so that we may
better estimate the required investments. Funding sources need to be fully explored.
Report compiled by:
Jon Henderson
GIS Manager