There are several key concepts developed through the master plan study of local stormwater in the Town of Lyons.
Since the 2013 Floods, there has been a number of studies on the hydrology of major watersheds within the State and in particular along the Front Range of Colorado. This study utilized the latest software and methods to evaluate the basins immediately affecting the Town of Lyons. Evaluations of the minor (2 year), intermediate, and major (100 year) storms were completed. Analysis of the basins included a scenario for wild fire, with consideration for the vegetation density and impact of charred earth on stormwater runoff. This hydrologic analysis can be a useful starting point for public and private studies of future stormwater detention, capture, conveyance, as well as redevelopment of Town of Lyons watersheds.
11.2 Land Use
The land use assumptions for this study determined the land use within the 2016 Town boundary is effectively built out. In other words, when comparing the existing impervious area with the impervious areas assumed by the future land use maps, the increase is less than 10% of the impervious area. Therefore, this study utilized the future land use impervious area for hydrologic and hydraulic computations. This is a unique, but not atypical, condition for a smaller front range community with the topographic constraints of Lyons. Consequently, development or redevelopment within the Town limits will not immediately invalidate the conclusions of this master plan.
Detention is a valuable means of slowing down stormwater, storing it for a short period of time, and releasing it in a controlled manner. However, the steep slopes and land use constraints in the Town have limited the feasibility of detention. Further evaluation of the detention facilities contemplated in the previous (1998) master plan identified several costly and complicated factors in the grading, stability, and available storage volume. Consequently, this master plan does not recommend significant benefit from detention facilities. However, if the Town expands into the upper elevations on the north side of Town development of new detention facilities should be recommended and carefully designed.
11.4 Water Quality
Stormwater master plans are quick to identify the major storm water risks and highlight the capital projects that can alleviate those risks. The nature of benefit-cost financing decisions forces communities to consider damages averted as a major element of the process. However, there are incremental damages that are more difficult to quantify with current technologies – water quality impairments for example. Therefore, it is prudent to consider the means and methods by which a community can improve water quality in the larger watersheds in which the community resides. This master plan has identified a number of smaller, achievable water quality improvements for the Town. The macro scale water quality ponds that can record an official water quality capture volume are as difficult to construct as the detention facilities on steep slopes in essentially built-out communities. Therefore, this master plan considers the greatest benefit to water quality will come through private, small-scale water quality installations throughout an engaged and caring community.
11.5 Public Outreach
This master plan was scoped to focus on engineering analysis to investigate the localized flood risk areas and evaluate mitigation alternatives. The public process was coordinated with Town staff and consultants and included presentations at the Utility and Engineering Board, Board of Trustees, and meetings with concerned citizens and neighbors. The public input to the process is essential in validating the assumptions used to model the flood risks throughout areas of complicated terrain, infrastructure, and changing ground conditions due to flood recovery and construction projects. Given the dynamic nature of flood recovery projects and the current economic environment, the public outreach for this particular master plan must continue through at least the planned completion of flood recovery projects in March 2018. At that time, the regional projects and plans on the North and South St. Vrain Rivers will be substantially completed. Evaluation and future implementation of the stormwater master plan will be influenced by completion of the major river projects. The online version of the master includes a ‘click-to-comment’ function that allows users to add stormwater master plan comments that get stored in a single database. This commenting function, as well as the Town’s ongoing attention to stormwater related matters, ensures this stormwater master plan has a long shelf life.
11.6 Operation and Maintenance
Operation and maintenance is always a key element to any stormwater plan. When the CIP projects reach nearly impossible budget figures, or when the priorities for other municipal infrastructure out rank surface drainage improvements, or when the best projects don’t get built for another 10 years, the operation and maintenance of the existing system continues. The Town’s existing stormwater system is functional despite limited capacity and generally disconnected conveyance systems. Therefore, resilience to flood risks can still improve even if it is only maintenance activities on the existing system. Trash removal, debris clean up, sediment removal, pipe maintenance, inlet cleaning, gutter pan replacements, and other routine tasks are the preeminent recommendation of the stormwater master plan.
11.7 Next Steps
The next steps for the Town of Lyons stormwater master plan include a frequent and routine review of the projects, priorities, and plans set forth in this document. This document in and of itself cannot solve a stormwater problem, avert flood risk, or increase resilience in the community. But, when this plan is paired with other planning efforts, included in development discussions, use of the technical appendices in evaluation of future projects, or other citations this plan can add value and clarity to stormwater management discussions in the Town of Lyons for many years to come.