Ken Mitchell Open Space Master Plan City of Brighton, Colorado Shalkey & Team, Inc. ERO Resources Corp Icon Engineering, Inc. October, 2006 Acknowledgements Ken Mitchell Open Space Master Plan This Master Plan was commissioned to the consulting landscape architecture and plan- ning firm of Shalkey & Team, Inc., by the City of Brighton on September 23, 2005, and submitted complete to the City on October 31, 2006. Sub-consultants ERO Resources Corporation and Icon Engineering, Inc., assisted Shalkey & Team with project planning. In addition to Brighton City Council and Park and Recreation Advisory Boards, the plan- ning team consisted of the following Brighton City Staff: John Bramble, City Manager Gary Wardle, Director of Parks and Recreation Mark Heidt, Assistant Director, Department of Parks and Recreation Terry Benton, Director of Public Works Dawn Hessheimer, Department of Public Works Water Specialist Respectfully Submitted: Edward J. Shalkey, President Shalkey & Team, Inc. 820 16th St., Denver, CO, 80202, (303) 820-3340 i Table of Contents Ken Mitchell Open Space Master Plan I. INTRODUCTION Overview of the Physical Resource. .1 Map No. 1 - Overview. .2 Overview of the Planning Program . .3 II. PLANNING PROGRAM . .5 Preliminary Program . .5 Final Program . .5 III. SITE INVENTORY. .6 Map No. 2 - Aerial Photograph . .7 Map No. 3 - Topographic Map . .8 Map No. 4 - Regional Context . .9 Map No. 5 - Land Ownership . .10 Map No. 6 - Natural Resources. .11 Natural Resources Site Review . .12 Map No. 7 - Existing Utilities . 19 Map No. 8 - Proposed Water Management Improvements. .20 Map No. 9 - Urban Drainage and Flood Control District Projects . .21 IV. MASTER SITE DEVELOPMENT PLAN . .22 Graphic No. 1 - Master Site Development Plan . .23 Graphic No. 2 - Southeast Corner Enlargement . .24 Figure No. 1 - Band Shell Concept . .25 Figure No. 2 - Paintball Field Concept . .25 Graphic No. 3 - Beach and Grand Pier Enlargement . .26 Figure No. 3 - Grand Fishing Access Pier Concept . .27 Graphic No. 4 - Grand Fishing Access Pier Enlargement. .28 Figure No. 4 - Ken Mitchell Park Site Concept . .29 Figure No. 5 - Pump House Concept . .29 V. RECORD OF PUBLIC PROCESS . .30 Figure No. 6 - Overflow Culvert Concept. .33 VI. COST ESTIMATE. .33 Map No. 10 - Cost Estimating Areas. .34 ii I. INTRODUCTION Overview of the Physical Resource: The Ken Mitchell Open Space Planning Area consists generally of a combination of four future, currently active and recently depleted gravel mining quarry cells; a total of approximately 607 acres of publicly and privately owned land and water resource. Land currently under the City’s control, including Cells No. 1, 2 and 3, Ken Mitchell Park and the quarry operator’s yard, total approximately 434 acres, 170 acres of which will be water when all proposed water storage cells are full. The Ken Mitchell Open Space Planning Area is generally located east of the South Platte River (the Platte forms the western boundary of the project), south of Colorado Highway 7, north of 144th Ave, and west of Brighton Road. Practically the entire planning area, except for the gravel operation’s quarry yard lies within the 100 year floodplain. See Map No.1, Overview, next page. Configuration of Land and Water: Three of the gravel mining cells, and the operator’s quarry yard were acquired by the City of Brighton in 1988 for the dual purpose of augmentation of water storage and public access open space. The City has a First Right of Refusal agreement in place to purchase Erger’s Cell for the same purposes when it is depleted. Quarry Cells No. 1, and No. 2 are depleted of gravel and are in various stages of engineering preparation by the City of Brighton for water storage purposes. A land bridge separates a portion of the east side of Cell No 1. from the west side. This land bridge will remain in place to facilitate a conveyor belt until the quarry operator depletes Erger’s Cell (10 to 20 years), then it will be removed. Cell No. 3 is currently being mined and also expected to be in operation for another 10 to 20 years. Erger’s Cell is being pre- pared for mining activities at the time of this writing. Characterization of the Water Storage Cells: The existing and planned gravel quarry cells will be utilized by the City to store water for augmenta- tion purposes. This means significant draw-downs in stored water elevations whenever the City needs to release water to the South Platte River to satisfy water calls from water users with more senior rights than the City. Other similar City reservoirs have been known to almost completely empty or refill their stored volume in a matter of a few weeks. The combined practicality of most efficient mining operations and most efficient water storage mean the edges of the storage cells, when completed, will be configured of steep (mostly between 2:1 and 3:1) slopes. The south to north sloping gradient of the South Platte River means that the maximum water level in each cell will be about 3 ft. lower than the cell adjacent to it on the south. The water storage function of these four cells will require that each cell be connected to the adjacent cell with a spillway (for flood events), and culverts (for normal high water movement). Each cell will be con- nected to the South Platte River with a spillway so that water can be safely managed into and out of the cells during flood events. The four cells will be supplied via the proposed 144th Avenue Augmentation Pipeline Project and two pumping stations between the South Platte River and Cells No. 1 and No. 3. A pumping station and outlet tower at the northwest corner of Cell No. 1 will facilitate water flows from the storage cells back to the South Platte River. 1 Map No. 1 - Overview 2 The Urban Drainage and Flood Control District (UDFCD) have plans to construct several streambank stabilization projects and a drop structure project on the reach of the South Platte River adjacent to the project study area. The land bridge between Cells No. 2 and No. 3 contains a gas line easement, and has been proposed by UDFCD as a conveyance corridor for the base flow of Third Creek (flood flows would be routed into Cells No. 2 and/or No. 3) between the east side of the project study area and the South Platte River. Existing Gas Well: An existing gas well, with a storage tank surrounded by chain link fence, exists on the west side of Cell 1, between the west edge of the cell and the South Platte River. Maintenance access by the well owner (or their representative) needs to be maintained to this well. Other Lands in the Study Area: The gravel mine operator maintains approximately 20 acres of yard space, including material stockpiles, screens, scales and similar mining equipment and installations. Existing City Recreational Improvements: The City of Brighton maintains two existing improvements and a trail along the northeast border of the project study area. The South Platte River Trailhead is a modest parking facility with an informational kiosk, which accesses a section of concrete hiking trail leading out of the project study area to the north. This trail segment, when joined to a future trail leading to the south through the Adams County Regional Park, will complete an important missing link in the Colorado Front Range Trail. Just south of the South Platte River Trailhead facility and adjacent to Cell 1 is the existing Ken Mitchell Park. This is approxi- mately a 8 acre, linear neighborhood park with a small asphalt parking area, a modest playground, a multi-purpose irrigated turf field, an asphalt basketball court and a few picnic tables and grills located in a sparse bosque of juvenile shade trees. More detailed inventory and analysis of the planning area’s physical resources is included in Section III. Overview of the Planning Program: A strong programming philosophy emerged during the public consensus building process associated with project planning. This philosophy was a result of a series of insightful comments from the public (mostly neighborhood), City Parks and Public Works staff, City Council and the Parks and Recreation Advisory Board. The general consensus which lead to the program for development discussed in Section II con- sisted of the following governing elements: Water Storage: The augmentation water management requirements of the project are relatively rigid, and so will be the function and placement of the necessary public works improvements needed to facilitate management (spillways, culverts, pump houses, etc.), but there may be considerably more flexibility in managing the appearance of these structures. The storage cell lakes will resemble cereal bowls more than natural bodies of water, and the lake levels are anticipated to fluctuate considerably on a seasonal basis. The planning team was properly advised to resist the urge to turn the storage cells into amusement sites, in favor of preserving them passively as they are; large scale natural resource deposits, imperfections and all. 3 Because of the dangerous configuration of the edges of the storage cells (3:1 or steeper), and the fluctu- ating water levels, human contact with the water resource should be limited to fishing from the shore or from piers, and non-motorized boating. Much Water, Little Land: The location and configuration of the storage cell lakes, with little land separating one cell from another and each cell from the site’s property line in most locations, will result in much water surface and com- paratively little land to support access to the water. And, the land resource remaining available around the margins of the storage cell lakes will be unusually thin and linear in configuration.