Towards improved forest management practices: high-resolution flow-channel and wet-areas mapping,

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1 Towards improved forest management practices: high-resolution flow-channel and wet-areas mapping, Paul A. Arp, Jae Ogilvie, Mark Castonguay, University of New Brunswick, Fredericton, New Brunswick; November 1, 2006 Highlights Digital elevation models (DEMs), when forced to comply with already mapped hydrographic features (streams, lakes, shorelines), can produce realistic delineations of small-scale catchment areas, flow channels, depressions, and wet areas, at 10 m resolution, or better. In forest management, these delineations are useful for surprise-free operations planning, implementation, and verification. Thus far, these delineations have led to: greater efficiencies in office-field communications, forest cutblock lay-out designs and harvesting, road and trail construction, tree planting, wetland classification, source-sink pathway identification, timber cruising, and off-road navigation. High-resolution flow-channel and wet-areas mapping is in the process of becoming a precision tool for FMA-wide operations planning. Typically, two components are needed: an FMA-wide digital elevation model (DEM), and related hydrographic features map (depicting all lakes, streams, islands, shorelines, etc.). Appropriate data processing of these produces: - a seamless network for mapping all already mapped and unmapped flow channels - a means to automatically draw watershed areas above any point along a stream, and above intended and existing road-stream crossings in particular - a way to locate most as yet unmapped depressions and wetlands - an approximate depth-to-water surface, at high and low water marks - a high-resolution means to display soil drainage conditions, and associated soil types - a framework for adding additional data layers and surface images, which in turn - are useful for refining and updating the original maps that may have been drawn from coarse-gridded DEMs and incomplete digitization of hydrographic features - ways and means to verify the mapped information, using various methods based on remote sensing, on-site investigations, and GPS tracking of, e.g., stream channels, soil disturbance fields, culvert locations, and vegetation boundaries The mapping process The principal flow-channel, wet-areas, and depth-to-water modeling and mapping stages are displayed in the following diagram: Wet-areas mapping principle DEM surface (interpolated) Depth to surface water DEM grid points Water -surface DEM: all waterbodies connected with one another, at the high water mark Delineate flow accumulation Add hydrographic features Determine depth to water (white 0, red 1 m) 1

2 Shown below is a 3-dimensional example of the modeling and mapping outcome, by focusing on an air-photo off Comeau Point, near Shediac, New Brunswick. Green areas are officially recognized wetlands (in this case, sand bars and tidal marshes), purple refers to areas where water would be close to the soil surface during wet seasons (dark purple: 1 m, light purple, 0 m). Red lines: expected as yet unmapped flow channels. Note that the DEM rendition of the area, based on an irregular 35 m xyz data grid, is sufficiently accurate to correspond with the steep coastline features of the air photo (air photo registration has a 6 m accuracy). In general, the above modeling and mapping process provides a depth-to-water metric, where depth refers to the elevation rise next to all mapped surface-water features, assuming that these features are filled with water, up to the banks and lake, river, island and ocean shorelines. To this end, high-resolution DEMs are better than coarse-gridded DEMs, but even coarse-gridded DEMs (e.g., 70 to 100 m spacings) can lead to useful and cost-effective applications, provided the coarse-gridded DEMs and hydrographic data layers are free of artifacts and errors. Mapping challenges There are many challenges regarding detailed flow-channel and wet-areas mapping. Here are a few issues in review: - The DEM and hydrographic layers need to be positioned correctly within the geographic projection system of choice; otherwise, there will be misalignments. - Even with correct geographic positioning, there needs to be conformity between all already mapped features (lakes, streams, rivers, shorelines, islands, roads) and the DEM grid. - When this does not occur, there may be inadvertent distortions in the DEM, or there may have been inconsistent attention given to detail in the hydrographic digitization process. - There is often a lack of systematic connectedness or continuity between vectorized stream and lake segments. Breaks in continuity need to be real. Artificial breaks will cause errors in the hydrographically corrected flow accumulation algorithm. - Lack of connections may only become apparent through pixel-to-pixel examination of the digitization work. 2

3 - DEM grids (xyz) may contain holes and spikes. Uncorrected xyz spikes can produce ripple effects within the geospatial interpolation process. - Geospatially interpolated DEMs may contain additional artifacts, leading to straight-line flow features. All these artifacts need to be eliminated to avoid problems in correctly delineating watershed boundaries and flow channels. Map reliability The same GIS framework that allows for the automatic derivation of all mapped and unmapped flow channels and wet areas also facilitates the reliability checking of the data that are actually needed for the mapping process. This is done by aligning other information that sheds light on the veracity of what has been mapped. The following summarizes a number of useful verification activities: - Post-harvest ortho-rectified surface images revealed much detail about local flow channels and wet areas; overlaying these images on top of the wet-areas map generally showed good alignments. - Overlaying GPS-ed culvert locations (e.g. stream road crossings) indicated an average agreement of location within 50 m or better. This agreement increased with increasing slope, and with increasing DEM resolution. - Assessing frequency of tree blow-down along the cutting edge of cutovers revealed a preponderance of tree blowdown in areas where the cutting edge traversed wet ground, as mapped. - GPS-tracing of wetland-upland transitions along the border of bogs (noted by the presence/absence of sphagnum), marshes were typically within 35 m of the mapped features. - Overlaying already classified wetlands map on the new wet-areas map showed a consistent and deep nestedness of classified wetland features within the areas mapped to be wet; in addition, the new map reveals the overall connectedness between the classified wetland features. - Soil cone penetrometers were found useful for verifying transitions between good and poor soil trafficability. - The 0 to 1m depth-to-water delineations were generally consistent with local soil drainage conditions, as revealed through soil pits along upland-wetland transects, with 0-10 cm corresponding to poor drainage, and 5-100cm corresponding to moderately-well drainage. Mapped depth-to-surface-water depends not only on the exact delineation of lake, river, island and shorelines features, but also on the exact time when the images used for digitization were taken. Taken such images at another time would reveal change in shoreline features, in concert with rising or falling water tables, ebb and tide, flooding or droughts. If DEMs were available for all surface features, whether currently flooded or not, low tide or high tide, if would then in principle be possible to capture the dynamic nature of the shorelines as well, based on what-if scenarios regarding rising sea levels, or increased or decreased water levels in lakes and rivers. Whether or not all newly mapped flow channels lead to visible channels in the field is a function of substrate type and permeability, the related infiltration capacities at each location, and the timing and amount of incoming precipitation, snowmelt, or flood waters. For example, areas overlain by compacted till, or impervious bedrock, tend to produce flow channels with 4 ha catchments areas, and smaller. With coarse substrates, flow channels are generally found along the predicted flow paths, but underneath the soil surface, generally at the regolith-bedrock interface. In principle, topographically derived flow channels cannot not capture all possible paths by which water flows in the landscape. Sub-surface flow paths that do not conform to surface topography are omitted because predicting these requires not-readily accessed or available information about subterranean flow conditions and geometries, especially for areas with highly permeable terrains and region-wide aquifer flows. However, the systematic digitization of all water surfaces from surface images produces an empirically benchmark for connecting most water surfaces across the landscape. 3

4 Areas mapped Shown below is a map of UNB-developed wet-areas mapping initiatives, from Newfoundland to British Columbia, and also Maine and Vermont, USA. Triton Brook Alpac Georgia Basin, BC Millar Western FMA Kamloops, BC Duck Mountain Moose Cree Nagagami Romeo Malette Vermont Nova Scotia, New Brunswick Maine Map showing locations for demonstrating the utility of the UNB-developed process for modeling and mapping hydrologically sensitive areas. The following areas have been mapped, or are in progress, including making further improvements: - New Brunswick - Nova Scotia - Maine - Vermont - Newfoundland: Triton Brook (474,000 ha); - Ontario: Nagagami FMA, Abitibi (470,000 ha); - Ontario: Romeo Malette Forest, Tembec (693,000 ha); - Manitoba: Ducks Mountain, LP and DU (377,000 ha). - Ontario: Moose Cree FMA, Moose Cree FN (900,000 ha); 4

5 Triton Brook, Newfoundland: general overview of the high-resolution flow-channel, wet-areas and depth-towater map for the Triton Brook Watershed Project (insert, top left), Newfoundland. This area is characterized by fairly flat plateaus and deeply incised valleys. The mapping process reveals many as yet unmapped streams, and also delineates areas that are wet most of the time. The above shows: the local LANDSAT image (purple: recent harvests), the official stream and lake network (dark blue), the newly mapped channels (thin lines, light blue), depth-to-water (0 to 1 m, pink to red, respectively), and hill-shading of local DEM. Research associated with the Triton Brook Watershed Project (near Gander and Grand Falls, Newfoundland) is part of a priority component of the sustainable forest management strategy of the Government of Newfoundland and Labrador. 5

6 Abitibi s Nagagami FMA: a small sample of the high-resolution flow-channel, wet-areas and depth-to-water mapping for the Nagagami FMA, Abitibi, Ontario. This area is characterized by hilly to undulating terrain with many as-yet unmapped streams and wet areas. Top: local air-photo mosaic, overlain by: road map (yellow), and stream and lake network (light blue). Bottom: the same except overlain with the newly mapped channels (thin lines), depth-towater (0 to 1 m, pink to red, respectively, at 10 m resolution). Abitibi has been supplied with a map covering the entire FMA. There has been a request to do the same for the Abitibi Iroquois Falls FMA. 6

7 Tembec s Romeo Malette Forest: 2 map examples, showing depth-to-water map (0 to 1 m, pink to red, respectively, at 10 m resolution), overlain with GPSed harvest tracks (source: FERIC, c/o Mark Partington), by month of operation. Top: a winter harvest; bottom: a summer harvest. Future research will evaluate extent of soil disturbance in relation to soil trafficability, time of operations, and related high-resolution navigation guidelines to avoid inadvertent soil disturbance. 7

8 Duck Mountain: sample area showing already mapped lakes and streams in light blue; newly mapped channels in dark blue, and roads (yellow). A comparison was made between Duck s Unlimited wetland classification (c/o C. Smith) with the flow-channel and wet-area delineation of the UNB mapping process. As show below, this comparison is promising in terms of allowing further refinements with regard to the wetland classification and the wet-area mapping process: the wet-areas map can be used as filter to remove erroneous pixilation symptomatic of unsupervised image classification, and the wetland classification can be used to correct and add small-to-large open-water features to the wet-area delineation process. The end result will be a topographically and hydrographically correct wet-areas continuum, with discrete wetland features embedded within this continuum. 8

9 Duck Mountain: Comparison of flow-channel, wet-areas and depth-to-water map with DU s wetland classification. Top: wet-areas map on top of wetland classification. Bottom: the reverse. 9

10 Outlook: All of the SFMN demonstrations areas are expected to be mapped by May Research on these areas will continue with ground and other verification, including comparisons with air photos and satellite and RADAR images. Two of the demonstration areas (Romeo Malette Forest, select townships in Northern Alberta) will be modeled and mapped intensively in terms of: - hydrological changes regarding depth to water, by season, weather and climate; - extent of soil disturbance fields in relation to mapped flow channels and depth-to-water; - relevance of modeling / mapping efforts in terms of FN values. The mapping process itself is subject to further refinements with respect to mapping reliability and accuracy, esp. in view of the coarse-gridded nature of provincial DEM coverages, and in view that LiDAR-based DEMs and new surface images that may become available for detailed examinations and quantification. Partners provide feedback to researchers regarding the utility of the maps, and may engage in map utilization, following the established leads by JD Irving, Bowater, and Millar Western. First Nations (Moose Cree, Kamloops Indian Band, and others) are encouraged to examine the utility of their FMA-wide maps with regard to forest management, community and traditional values planning. Acknowledgements: The authors acknowledge the assistance of Service New Brunswick and the New Brunswick Department of Natural Resources in providing up-to-date layers for the development of the UNB modeling and mapping process (MR-SID, original and re-sampled DEMs, road and stream layers). The development of highresolution mapping of flow channels, wet areas and depth-to-water was financially supported by the Nexfor-Bowater Forest Watershed Research Centre, with supplementary support from the New Brunswick Forest Products Association (NBFPA), the Nova Scotia Forest Alliance (NFA), the Fundy Model Forest (FMF), JD. Irving, the Forest Resource Improvement Association of Alberta (FRIAA), COMERN (Cooperative Mercury research Network), and an NSERC Discovery grant to P. Arp. Special thanks go to JD Irving and Bowater personnel for enthusiastically adopting the GIS flow-channel and wet-areas mapping framework, and incorporating this into daily forest operations routines. We are grateful to the SFMN network for allowing us to further refine and extend this study across Canada, by way of academic, governmental and industrial partnership support. The timely facilitation and / or compilation of geospatial data by Peter Hearns (Newfoundland DNR), George Schultz and Paul Poschmann, (Abitibi), Ken Durst (Tembec), John Turner (Moose Cree FN), Stephen Pearce (MONR), Marc Stevenson (U. Alberta), Margaret Donnelly, Stephen Hills and Donna Grassia (LP), Arnold Rudy (KBM Forestry Consultants Inc.), Elston Dzus and Mark Spafford (Alpac), Silvie Forest, Chris Smith and Eric Butterworth (DU), Barry White (ASRD), and Rita Winkler (BCMF) is much appreciated. Background Reading Andison, D.W Tactical forest planning and landscape design, p , In Burton, P.J., Messier, C., Smith, D.W.and Adamowicz, W.L., eds. Towards sustainable management of the boreal forest. National Research Council of Canada, Ottawa. Case, B.S., Meng, F.-R.and Arp, P.A Digital elevation modelling of soil type and drainage within small forested catchments. Canadian Journal of Soil Science 85: Clarke, S.and Burnett, K Comparison of digital elevation models for aquatic data development. Photogrammetric Engineering and Remote Sensing 69: Gessler, P.E., Chadwick, O.A., F., C., Althouse, L.and Holmes, K Modeling soil-landscape and ecosystem properties using terrain attributes. Soil Science Society of America Journal 64: Pulkki, R Minimizing negative environmental impacts of forest harvesting operations, p , In Burton, P.J., Messier, C., Smith, D.W.and Adamowicz, W.L., eds. Towards sustainable management of the boreal forest. National Research Council of Canada, Ottawa. Underwood, J. and Crystal, R.E Hydrologically enhanced, high-resolution DEMs [Online]. Available by Geospatial Solutions (posted April 1, 2002). 10