Title
Consider adopting Ordinance No. 3687, amending Code of Ordinances Sec. 86-600 regarding the adoption of a storm drainage design manual and Sec. 86-610 relating to regulation of stormwater detention and retention facilities, and take appropriate action
Body
BACKGROUND:
On September 3, 2019 City Council adopted a storm drainage design manual under Ordinance 3595. This manual set the design criteria for runoff coefficients and rainfall intensities required for the design of drainage facilities for all private and public development projects. The approval of this ordinance was planned to be a two-step process. Step one was to establish basic storm drainage criteria for all projects in order to comply with HB 3167. Step two was, upon completion of the Freese & Nichols detention study, to amend the storm drainage manual for the purposes of requiring detention and to assure compliance with the updated Municipal Separate Storm Sewer System (MS4) Program.
DISCUSSION:
The currently adopted storm drainage design manual was established to assist with the City’s procedures relative to storm water discharge for new development, redevelopment, and creek improvements. This manual sets the design criteria such as runoff coefficients and rainfall intensities required for the design of drainage facilities. The proposed Storm Drainage Design Manual updates the basic overall structure and layout of the Manual, and includes additional detail and the following major changes:
Chapter 4 - Requirement of detention for all sites that exceeded a runoff coefficient of 0.7. Any site that requires a runoff coefficient higher than 0.7, as established in Table 2 of the manual, shall detain the difference between 0.7 and the coefficient in Table 2. In most cases this will be commercial/industrial projects, which typically have a 0.9 runoff coefficient. This will result in an approximate 20% reduction in storm water runoff from individual sites.
Chapter 6 - Stormwater Quality. This was added to include post-construction, permanent facility maintenance, and temporary construction control requirements for storm water runoff.
The post-construction section references requirements for preparation of a stormwater quality management plan per the City’s Post-Construction Ordinance. As part of this, there is a new requirement for detention facilities to be designed to control the 1-year storm, a regionally accepted standard for water quality.
FISCAL IMPACT:
No Financial Impact
RECOMMENDATION:
City Administration recommends adopting Ordinance No. 3687, amending Ordinance No. 3595 of the City’s Code of Ordinances, Chapter 86, Utilities, Article VII, Municipal Drainage Utility System, Stormwater Drainage Requirements adopting an updated storm drainage design manual and related regulations.
POSSIBLE COUNCIL ACTION:
1. I move to adopt Ordinance No. 3687.
2. I move to adopt Ordinance No. 3687, with modifications.
3. I move to table the issue for further study or take no action.
ATTACHMENT(S):
1. Ordinance No. 3687
2. Storm Drainage Design Manual