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Applicant's Response to Second Adequacy Letter Grand River Park Project, DRMS File M-2006-046 January 2, 2007 Page 23 of interstate 70, and that historic clearance of canopy trees was particularly concentrated in the northeastern areas of the subject property, where a considerable amount of borrow material was taken and the floodway levee was constructed. The applicant's revised plans depict a "Cottonwood Dominated Riparian Area" in the northeastern zone of concern, with two stands of trees, one the applicant's property and a larger stand (of less than two acres in size) on the property of the adjacent land owner to the east (Valley Farm, Inc.). The applicant has provided an on-site buffer of nearly 200 feet from its own stand of cottonwoods; in addition to this buffer, the applicant has provided for a mix of native woody vegetation as a component of the revised reclamation plan, which will at least replace any senescent cottonwood trees. The applicant is unaware of specific concerns regarding riparian cottonwoods on the part of Valley Farms, Inc. (e.g., the land owner did not submit comment or objection to the Division during the comment period). Nonetheless, the applicant will assume that those trees have some inherent value as property that is subject to the Division's regulatory protection. In this case, the Division suggests that the groundwater model of mining conditions by Martin & Wood indicates that the applicant must develop a specific mitigation plan to protect those trees from life- threatening potential injury. Please note, however, that it is not anticipated that a sustained drawdown will occur in the six to eight foot range as indicated on the groundwater model. Between the adjacent cottonwood stand and the subject property, there is a side channel of the Colorado River {estimated to be no less than 50 cfs in year-round baseline flow, based on observed summer and fall stream conditions). This type offine-grained feature was not accounted for in the conservative-but-coarse model generated for planning purposes. Due to the presence of this side channel, a hydraulic break exists that will protect the adjacent cottonwood stand in all but pronounced drought conditions. As a precautionary measure, based on the Division's request, basic monitoring will be applied to both stands of cottonwoods. The Divison's referenced article ("Responses of Riparian Cottonwoods to Alluvial Water Table Declines") concludes that, "Monitoring annual branch growth appears to be the single best indicator of sublethal water stress in Populus. Furthermore, leaf senescence, desiccation, and shedding are an effective way of detecting the onset of severe water stress, and monitoring of live crown volume can be used to predict impending mortality under conditions of prolonged water stress." Plant disease and mortality have many possible causes, but it is intended that asemi-annual or more frequent monitoring program that collects representative data on branch growth and at least one other tree stress indicator (from the above list; for example, tree crown volume) will enable the operator to discern water-related stresses. Should both indicators signal that water table drawdown is a possible cause of stress to off-site native woody vegetation, the operator will, given permission by the adjacent owner to enter on those lands for the purpose of installing mitigation measures, revise the Water Management Plan to reallocate