No abstract

The rapid drainage of supraglacial lakes introduces large pulses of meltwater to the subglacial environment and creates moulins, surface-to-bed conduits for future melt. Introduction of water to the subglacial system has been shown to affect ice flow, and modeling suggests that variability in water supply and delivery to the subsurface play an important role in the development of the subglacial hydrologic system and its ability to enhance or mitigate ice flow. We developed a fully automated method for tracking meltwater and rapid drainages in large (> 0.125 km 2 ) perennial lakes and applied it to a 10 yr time series of ETM+ and MODIS imagery of an outlet glacier flow band in West Greenland. Results indicate interannual variability in maximum coverage and spatial evolution of total lake area. We identify 238 rapid drainage events, occurring most often at low (< 900 m) and middle (900-1200 m) elevations during periods of net filling or peak lake coverage. We observe a general progression of both lake filling and draining from lower to higher elevations but note that the timing of filling onset, peak coverage, and dissipation are also variable. Lake coverage is sensitive to air temperature, and warm years exhibit greater variability in both coverage evolution and rapid drainage. Mid-elevation drainages in 2011 coincide with large surface velocity increases at nearby GPS sites, though the relationships between ice-shed-scale dynamics and meltwater input are still unclear.Published by Copernicus Publications on behalf of the European Geosciences Union.

The prolonged history of industrialization, flood control, and hydropower production has led to the construction of 80,000 dams across the U.S. generating significant hydrologic, ecological, and social adjustments. With the increased ecological attention on re-establishing riverine connectivity, dam removal is becoming an important part of large-scale river restoration nationally, especially in New England, due to its early European settlement and history of waterpower-based industry. To capture the broader dimensions of dam removal, we constructed a GIS database of all inventoried dams in New England irrespective of size and reservoir volume to document the magnitude of fragmentation. We compared the characteristics of these existing dams to the attributes of all removed dams over the last ∼25 years. Our results reveal that the National Inventory of Dams significantly underestimates the actual number of dams (4,000 compared to >14,000). To combat the effects of these ecological barriers, dam removal in New England has been robust with 127 dams having been removed between ca. 1990-2013. These removed dams range in size, with the largest number (30%) ranging between 2-4 m high, but 22% of the removed dams were between 4-6 m. They are not isolated to small drainage basins: most drained watersheds between 100-1,000 km 2. Regionally, dam removal has reconnected ∼3% (3,770 river km) of the regional river network although primarily through a few select dams where abundant barrier-free river lengths occur, suggesting that a more strategic removal approach has the opportunity to enhance the magnitude and rate of river re-connection. Given the regional-scale restoration of forest cover and water quality over the past century, dam removal offers a significant opportunity to capitalize on these efforts, providing watershed scale restoration and enhancing watershed resilience in the face of significant regional and global anthropogenic changes.

2002) Statewide land cover derived from multi-seasonal Landsat TM data: a retrospective of the WISCLAND project. AbstractLandsat Thematic Mapper data were the basis in production of a statewide land cover dataset for Wisconsin, undertaken in partnership with USGS's Gap Analysis Program. The dataset contained seven classes comparable to Anderson Level I and 24 classes comparable to Anderson Levels II/III. Twelve scenes of dual-date TM data were processed with methods that included principal components analysis; stratification into spectrally consistent units; separate classification of upland, wetland, and urban areas; and a hybrid supervised/unsupervised classification called "guided clustering". The final data had overall accuracies of 94% for Anderson Level I upland classes, 77% for Level II/III upland classes, and 84% for Level II/III wetland classes. Classification accuracies for deciduous and coniferous forest were 95% and 93%, respectively, and forest species' overall accuracies ranged from 70 to 84%. Limited availability of acceptable imagery necessitated use of an early May date in a majority of scene pairs, perhaps contributing to lower accuracy for upland deciduous forest species. The mixed deciduous/coniferous forest class had the lowest accuracy, most likely due to distinctly classifying a purely mixed class. Mixed forest signatures containing oak were often confused with pure oak. Guided clustering was seen as an efficient classification method, especially at the tree species level, although its success relied in part on image dates, accurate ground truth, and some analyst intervention.