St. Croix River Crossing Project - Visual Quality Manual

Transcription

1 St. Croix River Crossing Project - Visual Quality Manual Minnesota TH 36/TH 95 Interchange 3.1 Context Existing TH 36/TH 95 Environment The proposed TH 36/TH 95 interchange will occupy a large area of land a few hundred feet west of the St. Croix River and 1.5 miles south of downtown Stillwater. TH 36 will pass over TH 95 at this new interchange, which will be located at the west end of the new river bridge. Trunk Highway 36 on the west side of TH 95 will be on fill, while TH 36 and ramps on the east side of TH 95 will be elevated on structure. Portions of the on ramp and off ramp west of TH 95 will be in cut sections. TH 95 accesses Stillwater to the north of the interchange and the cities of Bayport and Oak Park Heights to the south. A series of stormwater treatment ponds will be located at the interchange to receive runoff from the roadways. figure 3.1 Xcel Energy s King Generating Plant Various types of development occur in the vicinity of the TH 36/TH 95 interchange. The area directly northeast of the interchange is occupied by a sewage treatment plant and a marina/condominium complex. Southeast of the interchange, an Xcel Energy coal-fired generating plant occupies a large tract of land along the river (Figure 3.1). A residential neighborhood overlooks the interchange site from high ground to the northwest, and another residential area occupies high ground to the southwest. The interchange will be in the visual panorama of the historic St. Croix Overlook, which is situated about one third of a mile north of the interchange (Figure 3.2). As a result of the interchange location, motorists traveling TH 36 and TH 95 will have views of the sewage treatment plant and the generating plant, and residents in areas to the northwest and southwest will overlook the new roads and ramps. East of Osgood Avenue on TH 36 approaching the location of the planned TH 36/TH 95 interchange, the landscape character of the river valley begins to emerge. The existing TH 36 curves into TH 95, which figure 3.2 St. Croix Overlook 3-1

2 continues north to the Stillwater Historic District and the Lift Bridge. The curve clearly marks the transition from the TH 36 commercial area to the scenic St. Croix River Valley. The VQRC emphasized the natural features of this transitional area, including stone outcroppings and wooded areas. Some of the industrial development south of TH 36 and east of TH 95 was considered a negative aesthetic influence (these features include the regional wastewater treatment plant, the generating plant, and a State Prison). However, except for the generating plant chimney, these elements are fairly well screened by trees and so are not easily seen. Proceeding north along TH 95 into Stillwater, there is no clear entry statement into the city, but the Historic District soon becomes evident, beginning with the caves business area where building architecture is integrated with natural sandstone outcroppings. The balance of the downtown business district appears one or two blocks further north. The interchange will be developed on terrain made up of a series of slopes and terraces stepping up from the river. From a review of plant guides and by observing existing terrain features, the river terraces along the St. Croix were once characterized by diverse plant communities tied to a varied geology. Low-lying benches and bottomlands in the floodplain contained emergent marshes, bogs, prairie bottom or wet prairie, floodplain forest, and hardwood swamps. Intermediate and upper level terraces further from the river consisted of flat and gradually sloping ground, steep slopes and rocky bluffs between terraces, as well as ravines, seeps, and depressions. The larger flatter terraces may have been vegetated by prairie or oak savanna, but the steep slopes, ravines, seeps, and many terraces would likely have been covered by deciduous forest. Especially east facing slopes, which tend to stay shaded and moist, would have been dominated by forest. river terrace area where the proposed TH 36/TH 95 interchange will be constructed. Dense tree and shrub vegetation, however, still occupies the steep slopes, the base and the top of rock bluffs, and the margins of land between roads, railroads, and developed areas. Both sides of existing TH 95 are lined by deciduous trees and shrubs, which screen views of the sewage treatment plant, Sunnyside Marina, and generating plant (Figure 3.3). Roadsides along TH 95 have been described as leafy and green and lightly wooded, making for an attractive approach to the City of Stillwater. Bottomland trees and shrubs are common on the riverbank and lower terrace over which the new bridge approach will pass. On the west side of TH 95, a residential area that was cleared of homes in 1995 for construction is well shaded by upper story deciduous trees. Although the tree and shrub cover is fragmented over this river terrace landscape, the visual effect approximates that of a wooded terrain. figure 3.3 Vegetation Screens Views along TH 95 Human activity and development have eliminated much of the pre-settlement forest vegetation on the 3-2

3 Views to the river from the St. Croix Overlook are across treetops and foliage which largely obstruct the visual clutter of roads and development between the overlook and the river (Figure 3.4). A more thorough description of the overlook and its reconstruction is included in Chapter 8, Historical/Cultural Resources. Similarly, views from the river of the area that will be occupied by the interchange are of mostly trees. Views from residential areas above the proposed interchange are of what appears to be a tree covered landscape. Preservation of viewshed and visual quality from the overlook, river, and residential neighborhoods on the bluffs above the proposed interchange are an important consideration in the design of the interchange. The National Park Service and Minnesota State Historic Preservation Office have indicated that adverse impacts to views from the overlook and river are to be avoided to the greatest extent possible and, where adverse impacts are unavoidable, they be minimized and mitigated. A considerable amount of vegetation will be removed for construction of the TH 36/TH 95 interchange, its stormwater ponds, and structures. This vegetation currently screens a variety of man-made elements, and contributes to the semblance of a leafy and green landscape from various vantage points. Removal of these pockets and curtains of foliage will make the existing man-made elements and the new construction more visible. The character and quality of views from several locations, including from TH 36 and TH 95, will be significantly altered by construction of the new highway interchange. It is therefore important to reestablish the pockets and curtains of foliage to screen and attenuate the views in this area. 3.2 Evaluation Criteria and Guidance Input from the VQRC shaped the following evaluation criteria and goals for the TH 36/TH 95 interchange area: Maintain the sense of forested or wooded landscape Create a clear entry statement for Stillwater, extending north from the interchange along TH 95 Screen the negative visual features (nearby industrial development) figure 3.4 View East to River from St. Croix Overlook Narrow the visual field and manage traffic/speed (the interchange will include two intersections along TH 95 for the ramps connecting to TH 36 and the new river bridge) 3-3

4 3.3 Recommendations To maintain the wooded visual character of the TH 36/TH 95 interchange area landscape, open ground areas associated with the interchange should be densely planted with native trees and shrubs between and along roads and ramps (Figures 3.5, 3.6, and 3.7). Over time, this vegetation will attain sufficient height and density to visually screen many of the interchange features from the St. Croix Overlook, the river, and adjacent neighborhoods. Moreover, this restored vegetation will return a wooded character to the TH 95 corridor and will reduce the openness and scale of the interchange (Figures 3.8 and 3.9). In Figure 3.9, note the extent to which a bridge is screened by trees. The approaches to the new river bridge are similar in height to the bridge in this image. Figure 3.10 is a location map of the computer visualization of TH 95 shown in Figure Outward views for motorists will be primarily of forest plants indigenous to the St. Croix river terraces. A list of trees and shrubs for the interchange area is provided in Table 3.1. Native trees and shrubs should be planted, outside of the clear zones, between the various roadways, and also beneath the main bridge approach structure and the elevated ramp structures east of TH 95. Several species of deciduous trees and shrubs are suitable for the partial shade that will be cast by the high overhead roadway structures. Moving from west to east, vertical clearances under the elevated roadways will increase to the extent that tall growing trees can be planted beneath the bridge approaches. The elevated structures may slightly limit the amount of rainfall reaching the ground for plants; however, this reduction in precipitation will be slight due to windblown rain, surface runoff, and sufficient groundwater. Under the west (abutment) ends of the elevated structures, where vertical clearances are reduced, it will be appropriate to use mostly shade tolerant and drought resistant plants to vegetate these 3-4 table 3.1 Suggested Tree and Shrub List Common Name Lower Bench East of TH 95 Trees Green Ash Basswood Black Ash Red Oak Red Maple Silver Maple Cottonwood Shrubs American Hazelnut Gray Dogwood Pagoda Dogwood Speckled Alder Winterberry Upper Bench West of TH 95 Trees Red Oak Basswood White Oak Red Maple Sugar Maple Paper Birch Green Ash Shrubs Prickly Gooseberry Pagoda Dogwood Nannyberry Viburnum Red Elderberry Botanical Name Fraxinus pennsylvanica Tilia americana Fraxinus nigra Quercus rubra Acer rubrum Acer saccharinum Populus deltoides Corylus americana Cornus racemosa Cornus alternifolia Alnus incana Ilex verticillata Quercus rubra Tilia americana Quercus alba Acer rubrum Acer saccharum Betula papyrifera Fraxinus pennsylvanica Ribes cynosbati Cornus alternifolia Viburnum lentago Sambucus pubens

5 NORTH To Stillwater St. Croix River TH 36 Bridge Stormwater pond with naturalized edges Loop Trail Exit Ramp Existing Wetland TH 36 Beach Road Entrance Ramp TH 36 Bridge over TH 95 Entrance Ramp figure 3.5 Plan View of River Terrace Forest Landscape Concept for the TH 36/TH 95 Interchange Exit Ramp Stormwater storage/treatment pond as Natural Wetland or marsh scale in feet Upland oak savanna in vicinity of Beach Road TH 95 Deciduous trees & shrubs native to St. Croix River Terraces To Bayport 3-5

6 VQM figure 3.5 Plan View of River Terrace Forest Landscape Concept for the TH 36/TH 95 Interchange 3-5

7 Westbound Entrance Ramp from TH 95 TH 36 Eastbound & Westbound Lanes Eastbound Exit Ramp to TH 95 Stormwater Pond with Naturalized Edges Deciduous Trees & Shrubs Native to St. Croix River Valley scale in feet figure 3.6 Cross-Section Illustration of Landscape Concept for TH 36 in the TH 36/TH 95 Interchange figure 3.7 Cross-Section Illustration of Landscape Concept for TH 95 in the TH 36/TH 95 Interchange Stormwater Pond with Naturalized Edges Southbound Thru & Turn Lanes Northbound Thru & Turn Lanes Loop Trail Deciduous Trees & Shrubs Native to St. Croix River Terraces 3-7

8 VQM figure 3.6 Cross-Section Illustration of Landscape Concept for TH 36 in the TH 36/TH 95 Interchange figure 3.7 Cross-Section Illustration of Landscape Concept for TH 95 in the TH 36/TH 95 Interchange 3-7

9 areas. Near the abutments, a lack of precipitation to support plant growth may require ground areas to be stabilized with crushed rock, concrete, or rip rap. figure 3.8 Highway with Wooded Roadside Note clear zones along roadway In developing planting plans for the interchange, highway safety and maintenance concerns must be addressed. Plants will need to be positioned so they do not obstruct sight lines or impinge on clear zone setbacks and snow storage areas. While adhering to highway operational and safety requirements, the layout of plants near and along roadsides should be done in a way that creates an irregular or meandering edge, not a uniform edge that parallels the roadway. Also, along the roadsides, shrubs and lower story small trees should create a visual transition to larger, taller vegetation. Shrubs can potentially be planted in clear zones to create this irregular edge and vertical transition. It will be necessary to provide a mow strip between shrubs and roadway shoulder (Figure 3.12). Stormwater treatment ponds in and near the interchange should have the appearance of natural ponds, similar in character to the kettle ponds that occur nearby. Further discussion on the visual character of stormwater ponds and other drainage features is provided in Chapter 9, Design Elements. The new river bridge will include an anti-icing system. A building housing anti-icing equipment and materials for the river bridge will be located on the treatment plant access road under the river bridge. This location is well screened from the river and the roadways due to the lower elevation and mature vegetation. figure 3.9 Highway Bridge Structure in Wooded or Forested Landscape South of the interchange, toward Bayport, a retaining wall is required to support a trail west of the Pickett stormwater ponds. The length and location of the wall creates a strong visual image, see Figure Chapter 7, Loop Trail and Other Trails, Section 7.5.1, Minnesota TH 95 South, provides additional description of the treatment of the trail and wall. 3-9

10 figure 3.10 Location Map of Visualizations TH 95 will serve as an entrance or gateway to the cities of Stillwater, Oak Park Heights, and Bayport. Chapter 9, Design Elements, Section 9.9, Community Gateway Areas, discusses the purpose and examples of community gateways with recommendations for local gateway themes and elements. Further local involvement will be required to develop community gateway themes if the treatment is desired on these roadway segments. 3-10

11 figure 3.11 TH 95 Visualization 3-11

12 VQM figure 3.11 TH 95 Visualization 3-11

13 Large trees Roadway Low to medium shrubs Large shrubs and small trees figure 3.12 Cross-Section Illustration of Typical Planting Conditions along Highways and Ramps 3-13

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15 figure 3.13 Bayport Retaining Wall Visualization 3-15

16 VQM figure 3.13 Bayport Retaining Wall Visualization 3-15