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typically ends in late October, around the typical first freeze of late autumn. Cottonwood trees <br />usually start to get their leaves in early April, about one month before the last nocturnal frost of <br />the spring according to the article Nonresponse of notice cottonwood trees to water additions <br />during summer drought (Cox et al. 2010). This information indicates that even though cottonwood <br />trees typically have a high rate of transpiration, during the winter (dormant) dewatering period, <br />the transpiration period for the trees will have ended by the time dewatering activities begin. This <br />means that the trees will be using very little water since transpiration is not occurring. Dewatering <br />activities will have ended prior to the beginning of spring transpiration. <br />In Ecophysiology of riparian cottonwoods: stream flow dependency water relations and restoration <br />(Rood et al. 2002) it is discussed that cottonwood populations have declined, particularly in <br />response to dewatering as a result of irrigation during the hot, dry period of mid- to late summer. <br />We understand that causing a drought -like condition during the summer would be detrimental to <br />the health of the cottonwood trees. The project has scheduled the proposed dewatering activities <br />during winter when the trees are dormant, so tree stress and potential population decline is not <br />anticipated. <br />Supplemental water will be available to these trees through snowmelt throughout the winter (Cox <br />et al. 2010). illustrates that cottonwood trees may alternate water source use between <br />groundwater and surface soil moisture, and cottonwood trees have highly adaptable root systems <br />that have shown rapid growth in response to changes in water and nutrient availability. During <br />winter, the trees will be dormant and transpiration will not be active; however, any water the trees <br />will use can be supplemented by natural precipitation. Also, this particular site is on the bank of <br />the Animas River. The Animas River is part of the Colorado River System and is a major river <br />running through the Hermosa /Durango area. The watershed of the river includes the project area <br />and will provide water supply for these cottonwood trees during these winter dewatering periods. <br />As soon as dewatering is completed and spring is approaching, the Dillon Ranch Pit will be <br />returned to 90 percent capacity, providing the trees with water when the active growing season <br />begins. According to the groundwater hydrology report completed by Western Water and Land, it <br />is anticipated that ground water levels will be restored before transpiration begins in the spring. <br />Irrigation studies have been performed on cottonwood trees. During the study presented in the <br />article, On the irrigation requirements of cottonwood ( Populus fremontii and Populus deltoides <br />var. wislizenii) and willow (Salix gooddingii) grown in a desert environment (Hartwell et al. 2010), <br />cottonwoods were irrigated with only 0.88 millimeters (mm) of water per day (the equivalent of 1 <br />inch of water per month) during the dormant period of the year (September 15 — April 15) during <br />study period. This indicates that cottonwood trees do not require much water during winter <br />months. The conclusions of the study indicate that winter irrigation may not have even been <br />necessary as winter precipitation may have been enough to induce bud break in spring. <br />The Natural Resource Conservation Service (NRCS) identifies the soils where the majority of <br />these cottonwood trees are growing as `fluvaquents, sandy, frequently flooded.' These soils are <br />poorly drained, and the capacity of the most limiting layer to transmit water (Ksat) is moderately <br />high to high (0.20 to 6.00 inches per hour). So even with planned dewatering activities, it is likely <br />►7 <br />