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HomeMy WebLinkAboutRIVER DISTRICT BLOCK ONE MIXED-USE (ENCOMPASS) - PDP - PDP120020 - REPORTS - ENVIRONMENTAL REPORT (3)July 6, 2012 Rich Shannon Pinnacle Consulting Group, Inc. 5110 Granite Street, Suite C Loveland, CO 80538 RE: Ecological Characterization Study (ECS) Letter Report for the Block One Development Site Rich: This letter is submitted in response to Lindsay Ex’s request for a brief ECS Report summarizing my thoughts regarding the ecological features of the proposed development site for the Block One Project. The development site is situated between on the south side of Linden Street and adjacent to the west side of the Cache la Poudre (Poudre) River. Ecological characteristics of the property were reviewed during an on-site meeting with City of Fort Collins staff, you, and me on March 6, 2012. The proposed Block One mixed use development site has minimal ecological value and supports no natural habitat features. The majority of the property’s surface is paved with either concrete or asphalt. The few level unpaved surfaces and the embankment on the west side of the property have been cleared of native vegetation by past industrial activities and only support annual weeds such as cheatgrass (Bromus tectorum), field bindweed (Convolvulus arvensis), kochia (Bassia scoparia), common dandelion (Taraxacum officinale), and Russian thistle (Salsola tragus), as well as few Siberian elm (Ulmus pumila) seedlings. The property does not support any native vegetation, wetlands, or other unique habitat features. Features of ecological value within 500 feet of the development site consist primarily of the Cache la Poudre River and the riparian corridor supported along both sides of the river. The riparian corridor between the property boundary and the Poudre River is very narrow and most trees are growing on a very steep embankment. The embankment has been stabilized in the past with block of broken concrete. Trees supported on the embankment consist of seven Siberian elms, eight multi-trunked peachleaf willows (Salix amygdaloides), two eastern cottonwoods (Populus deltoides), and one small, multi-trunked ponderosa pine (Pinus ponderosa). Development of the Block One parcel would create no additional impacts to the Poudre River corridor beyond those that are already occurred from existing disturbance and development. The Block One project site is zoned RDR (River Downtown Redevelopment District) and City buffer zone standards (LUC 3.4.1) do not apply to RDR zones. Based on its current zone designation, lack of any natural habitat features, its location between existing development and roadways, and presence of pavement up to the top edge of the river embankment, the site could be enhance substantially by planting additional, appropriate native plant species between the top of the embankment and proposed development features. These plantings would create additional buffer between the proposed development and the river corridor. These plantings would also create additional habitat diversity (primarily for songbirds) and visual screening between the development parcel and the river. Native upland shrub and tree plantings would also establish a more natural vegetation transition zone between the river corridor and the proposed development. The site could be further enhanced by planting appropriate native and ornamental species along the new embankment that would be created along the western edge of the property boundary. A review of Natural Resources Conservation Service (NRCS, formerly SCS) soils mapping for the development site area indicates the Paoli fine sandy loam soil-mapping unit underlies the entire project site up to the river embankment. This is an upland soil that, in an undisturbed state, supports native short-grass prairie species such as blue grama (Bouteloua gracilis), little bluestem (Schizachyrium scoparium), and green needlegrass (Nasella viridula). As indicated by the riparian corridor on the project area side of the river corridor, this soil type can also support native cottonwood, willow trees and other riparian species when more mesic soil moisture levels are created by proximity to the river corridor. R. Shannon 7/2/12 Page 2 of 2 Based on these considerations the following mitigation recommendations are provided for the Block One development parcel. • The area between proposed development areas and the top of the river embankment should be planted with an upland riparian vegetation mix, including shrubs and trees, to create a transitional zone of native upland riparian vegetation. The goal of these plantings should be to create a self-sustaining, native vegetation community to stabilize soils and enhance wildlife habitat. Plantings of native shrubs and trees would also provide visual screening between development and important habitat areas. Habitat enhancement plantings would likely require soil treatment to relieve compaction (ripping) and improve fertility (fertilizer amendments). Supplemental irrigation would also be needed for initial establishment of native shrubs and trees. Suggested species for planting include the following deciduous trees and shrubs. Deciduous Trees Deciduous Shrubs eastern cottonwood (Populus deltoides) American plum (Prunus americana) lanceleaf cottonwood (Populus acuminata) big sagebrush (Artemisia tridentata) (both non-cotton bearing varieties) chokecherry (Prunus virginiana) netleaf hackberry (Celtis reticulata) golden currant (Ribes aureum) rubber rabbitbrush (Chrysothamnus nauseosus) serviceberry (Amelanchier alnifolia) skunkbrush sumac (Rhus trilobata) These species could also be used for native plantings on the slope to be created along the western property boundary • Maintain, to the extent possible, native trees on the river embankment that were determined to be significant by the City Forester (Tim Buchanon) these trees would also help to maintain slope stability. Removal of any trees classified as significant would need to be mitigated with replacement trees as per Section 3.2.1 (F) of the Land Use Code. • The intensity of night lighting from the sides of buildings facing the Poudre River corridor should be shielded or directed to minimize the intrusion of artificial nighttime light into this area. • One issue of concern for the property is the stability of the river embankment slope along the eastern property edge. Part of the development proposal is to remove the non-native Siberian elm trees along the river corridor to create a more native riparian corridor as well as to create some unobstructed views of the river from the proposed restaurant site. A concern with tree removal is that this may create stability issues with the existing steep embankment. In order to address this issue the project team retained Flywater, Inc. to evaluate the stability of the existing embankment as well as to determine of removing Siberian elms would create some instability issues. The Flywater report is included as an attachment to this report. In general the report concluded that Siberian elm removal would not create additional instability as long a additional rock armoring is placed in areas of existing undercutting along the toe of the river embankment. Rich, this concludes my evaluation of the Block One development site. If you have any questions or require additional input regarding my evaluation, please give me a call. Sincerely, CEDAR CREEK ASSOCIATES, INC. T. Michael Phelan, Principal attachment: Flywater, Inc. report !"#$"%#&’()#*)+,%# June 25, 2012 Mr. Jeff Jensen Jensen Consulting 37154 Dickerson Run Windsor, CO 80550 RE: BlockOne Mixed Use Project - Tree Removal and Bank Stabilization Along the West Bank of the Cache la Poudre River Near Linden Street. Mr. Jensen, You have contracted FlyWater to observe the existing bank of the Poudre River and provide recommendations for possibly removing non-native trees and resultant bank stability. I understand that your client is interested in developing the piece of ground downstream and adjacent to the west bank of the Cache la Poudre River on Linden Street. At this time, it is envisioned that a mixed use project that includes a restaurant may occupy the site. A walking trail and buffer vegetation is also proposed for the property between your clients and the river. Several non-native trees are being proposed for removal and the client as well as the City of Fort Collins is interested in the stability of the bank. OBSERVATIONS: I have several general observations of the site and the stability of the existing bank prior to presenting our recommendations. The first observation is that the site and the bank on which the trees may be removed is on the inside of a slight meander bend of the river. Inside bends tend to have less erosive action than outside bends and therefore tend be be more stable. Past practice of the concrete batch plant was to dump slag concrete down the bank that has essentially produced a paved slope. Therefore the embankment is well protected. However, the toe of the slope rarely if ever received the treatment and the existing slope paving is undercut significantly in several places along the bank bordering the proposed development. The existing embankment is also very steep (in some places steeper than 1:1 slope). BANK STABILITY: As mentioned above the existing stability of the banks appears to be good. There are several places in which 15 to 20 feet of the slope paving is being undercut from yearly flood flows. However, most of the places where there is undercutting, there are large cottonwood trees that provide stability and keep the slope paving in place. One area in which the undercutting may be a stability issue in the future is just upstream of a large siberian elm growing ¾ up the embankment and approximately 50 feet downstream of the Linden Street Bridge. This area has the most severe undercutting and is in an area not anchored by large trees. This is also just upstream of two siberian elms that may be removed. Please see Figures 1, 2, 3, and 4 showing undercut areas beginning with the undercut most likely to be an issue and continuing downstream to others that do not appear to be an issue while the cottonwoods are alive. !"#$"%#&’()#*)+,%# Figure 1: Upstream Most Undercut - Most Likely to Have Stability Issues Figure 2: Next Downstream Undercut - Just below Large Cottonwood !"#$"%#&’()#*)+,%# Figure 3: Next Downstream Undercut - High on Bank Between Two Cottonwoods Figure 4: Downstream Most Undercut - Adjacent to Large Cottonwood !"#$"%#&’()#*)+,%# PUBLIC SAFETY: Another observation is the existing slopes, while stable, are steep. A proposed path along the top of the bank adjacent to the development will provide access to the public. Most of the bank is heavily vegetated and will discourage public access to the river. However, the same area identified above as susceptible to undercutting instability due to lack of large vegetation, is also the area of most concern as the lack of vegetation provides a tempting access point to the riverside. RECOMMENDATIONS: Overall, the banks appear stable except for one area. Removal of non- native, Siberian elms will not adversely impact the overall bank stability if the toe of the slopes below the slope paving is secured. It is recommended that the toe of the slope be stabilized for an overall distance of approximately 85 feet with rock having a median diameter (D50) of 2.5 feet. The rock should be dug into the toe approximately 2*D50 and the top width of the treatment will vary from 3*D50 upstream to 1*D50 downstream. If the Siberian Elms are removed it is recommended that the trees be cut flush with the slope paving. While the roots will eventually rot, the process may take 20 or more years as the trees are growing fairly high on the bank and will rarely go through wet/dry cycles. If the toe of the slope is protected, the slope paving appears to be very stable. It is further recommended that along the 85 feet of toe protection, the top of the bank should be planted with dense, thorny shrubs to discourage public access. A plan view as well as cross section views are attached to this letter. Jeff, I appreciate the opportunity to be part of the team. If you have any questions or comments, please contact me at (970) 231-5498 or brad@flywater.com. Thank you, Brad Florentin, PE Vice - President FlyWater, inc.