- Email: [email protected]
Discussion: Comparison of slope instability screening tools following a large storm event and application to forest management and policy
Geomorphology 184 (2013) 154–155
Contents lists available at SciVerse ScienceDirect
Geomorphology journal homepage: www.elsevier.com/locate/geomorph
Discussion: Comparison of slope instability screening tools following a large storm event and application to forest management and policy Susan Shaw ⁎ Weyerhaeuser Company, P.O. Box 275, Springfield, OR 97477, United States
a r t i c l e
i n f o
Article history: Received 5 September 2012 Accepted 26 October 2012 Available online 22 November 2012 Keywords: Landslide Slope stability model Geographic information system (GIS) Forestry
a b s t r a c t The purpose of this discussion paper is to identify major technical errors made by Whittaker and McShane (2012) regarding the development and use of SLPSTAB (Shaw and Vaugeois, 1999; Vaugeois, 2000). SLPSTAB is a GIS-based data layer currently utilized as a regulatory tool for preliminarily screening slope stability potential on nonfederal, commercial timberlands in Washington State. © 2012 Elsevier B.V. All rights reserved.
Whittaker and McShane (2012) make several references to methods used to develop the SLPSTAB data layer. SLPSTAB currently is used by the Washington Department of Natural Resources (WDNR) as a preliminary screen of shallow landslide potential during its regulatory reviews of applications for proposed forest practices on nonfederal, commercial forestlands in western Washington, USA. As coauthor of Shaw and Vaugeois (1999) and codeveloper of SLPSTAB with Laura Vaugeois (deceased), I would like to correct several errors made in the paper by Whittaker and McShane (2012) regarding the data and models employed in creating the SLPSTAB screening tool and the intended use of this geographic information system (GIS) raster data set. First, Whittaker and McShane (2012) cite the WDNR GIS metadata file describing SLPSTAB (Vaugeois, 2000) that refers to the use of two models, SMORPH and SHALSTAB, in generating the SLPSTAB data layer. The current SLPSTAB grid layer (WDNR, 2007), however, was generated solely with the SMORPH model (Shaw and Johnson, 1995), which does not use climatic- or soil-parameter data explicitly in any aspect of its derivation or calibration. The SHALSTAB model (Montgomery and Dietrich, 1994) does employ these types of data and had we actually used this model in creating the SLPSTAB data layer, the Whittaker and McShane (2012) discussion regarding the benefits of more refined precipitation and soil-property algorithms would be relevant. Second, the reference to SHALSTAB in the GIS metadata file was intended as a placeholder for potential future data layer expansions but not necessarily as an indication of its use in the current version of SLPSTAB. As described in Shaw and Vaugeois (1999), statistically based comparisons of SMORPH and SHALSTAB landslide-probability distributions indicated that either model would work equally well ⁎ Tel.: +1 541 974 7805; fax: +1 541 988 0611. E-mail address: [email protected]. 0169-555X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.geomorph.2012.10.027
scientifically as a regulatory preliminary screening tool. The WDNR and the Washington Cooperative Monitoring, Evaluation, and Research Committee ultimately recommended to the Washington Forest Practices Board that the first version of the SLPSTAB layer be created using the SMORPH model because, unlike SHALSTAB at the time, this model (1) yielded output in terms of the regulatory decision-matrix criteria already established in Chapter 222-22(2)(iv) of the Washington Administrative Code (WAC; Washington Forest Practices Board, 2012a); (2) required no precipitation or soil-property rules to run; and (3) could be deployed immediately without modification to meet the mandates of Washington Engrossed Substitute House Bill 2091 and the Washington Forest and Fish Report (USDI et al., 1999). In addition, Shaw and Vaugeois (1999) found that the SHALSTAB model output was sensitive to the values of soil-property and hydrology input parameters, thereby making it challenging to assign input values representative of the large spatial and temporal variability in precipitation regimes and soil characteristics encountered at the regional (i.e., western Washington) scale. Notwithstanding, the SHALSTAB placeholder was preserved to accommodate the future use of this model, should the model authors elect to address these applied-management issues. Third, the SLPSTAB layer was created with a model designed to predict shallow-landslide potential and was calibrated solely with shallow landslide inventories (Shaw and Vaugeois, 1999; Vaugeois, unpublished document). Hence, SLPSTAB was not intended to be used in comparing model predictions of landslide potential with deep-seated or road-related landslide initiation points. The WDNR aerial-reconnaissance data used in Whittaker and McShane (2012) included all observed landslide types. Landslide type, however, is not listed in paper Section 2.1 as one of the criteria for sample selection. Whittaker and McShane (2012) would benefit from some clarification in this regard.
S. Shaw / Geomorphology 184 (2013) 154–155
Fourth, Washington State does not regulate forest practices on the basis of the SLPSTAB screening tool, in part because of data resolution issues associated with the digital elevation model (DEM) from which the tool is derived. The purpose of the SLPSTAB screening tool in a regulatory context, as described by Vaugeois and Shaw (2000), is to trigger a site geotechnical investigation by a qualified expert (Washington Forest Practices Board, 2012b) of any proposed forest practice that would occur on or within the vicinity of ground identified as potentially unstable by the data layer. SLPSTAB is not capable of pinpointing the exact location of existing and potential landslide initiation points because of horizontal and vertical inaccuracies in the DEM data. Most of the current SLPSTAB layer was produced using USGS 10-m DEM with a horizontal accuracy on the order of ±10.7 m (35 ft) (Vaugeois, 2000). Consequently, a grid cell representing a ‘high’ or ‘medium’ landslide probability rating could be offset spatially from an actual landslide initiation point, and limiting forest practices in that grid cell could result in misapplied ground protection (e.g., potentially not protecting the actual failure site). In the absence of any other field-verified site information, allowing the ‘high’ or ‘medium’ landslide-potential rating for any given grid cell to dictate the forest-practices classification or management prescription for the actual slope area represented by that cell would be counter to the purpose of SLPSTAB as stated in Vaugeois (2000). Furthermore, identifying the exact location of potential or existing landslide initiation points presently is beyond the capability of DEM-based topographic models where high resolution, LiDAR-derived DEM are not yet available (i.e., the majority of Washington commercial timberlands in steep, mountainous terrain). References Montgomery, D.R., Dietrich, W.E., 1994. A physically-based model for the topographic control on shallow landsliding. Water Resources Research 30, 1153–1171. Shaw, S.C., Johnson, D.A., 1995. Slope morphology model derived from digital elevation data. Proceedings, 1995 Northwest Arc/Info Users Conference, Oct. 23–25, Coeur d'Alene, ID (13 pp.).
155
Shaw, S.C., Vaugeois, L.M., 1999. Comparison of GIS-based Models of Shallow Landsliding for Application to Watershed Management. TFW-PR 10-99-001, #118 Washington Department of Natural Resources, Olympia, WA. (Available from: http://www.dnr. wa.gov/Publications/fp_tfw_pr10_99_001.pdf. Accessed 27 March 2012). U.S. Department of Interior (USDI) Fish and Wildlife Service, U.S. Department of Commerce National Oceanic and Atmospheric Administration, U.S. Environmental Protection Agency, Office of the Governor of the State of Washington, Washington Department of Natural Resources, Washington Department of Fish and Wildlife, Washington Department of Ecology, Washington State Association of Counties, Washington Forest Protection Association, Washington Farm Forestry Association, Colville Confederated Tribes, and other tribal governments, 1999. Forests and Fish Report. Prepared for the Washington Forest Practices Board and the Governor's Salmon Recovery Office. Washington Department of Natural Resources, Olympia, WA. (218 pp. Available from: http://www.dnr.wa.gov/BusinessPermits/Topics/ForestPracticesRules/Pages/fp_ffr.aspx. Accessed 27 March 2012). Vaugeois, L.M., 2000. SLPSTAB: modeled slope stability screen. Prepared by the Washington Department of Natural Resources, Olympia, WA. (Available from: (http://www.dnr.wa.gov/BusinessPermits/Topics/ForestPracticesApplications/Pages/ fp_gis_spatial_data.aspx) or (http://www.dnr.wa.gov/Publications/fp_data_slpstab_ meta.html). Accessed 27 March 2012). Vaugeois, L.M., unpublished document. Protocols Used for Developing the SLPSTAB Dataset in Western Washington. Archived by Washington Department of Natural Resources, Olympia, WA. Available from Leslie Lingley, Science Team Leader, Forest Practices Division, Washington Department of Natural Resources, Olympia, WA ([email protected]). Vaugeois, L.M., Shaw, S.C., 2000. Modeling shallow landslide potential for watershed management. 2000 ESRI User Conference Proceedings (Available from: http://proceedings. esri.com/library/userconf/proc00/professional/papers/PAP310/p310.htm. Accessed 27 March 2012). Washington Department of Natural Resources (WDNR), 2007. Forest practices application review system. Available from: http://fortress.wa.gov/dnr/app1/fpars/viewer. htm(Accessed 27 March 2012). Washington Forest Practices Board, 2012a. Title 222 WAC – forest practices rules, chapter 222-22 – watershed analysis. Available from: http://www.dnr.wa.gov/ Publications/fp_rules_ch222-22wac.pdf (Accessed 27 March 2012). Washington Forest Practices Board, 2012b. Title 222 WAC – forest practices rules, chapter 222-10 WAC – State Environmental Policy Act Guidelines. Available from: http:// www.dnr.wa.gov/Publications/fp_rules_ch222-10wac.pdf (Accessed 27 March 2012). Whittaker, K.A., McShane, D., 2012. Comparison of slope instability screening tools following a large storm event and application to forest management and policy. Geomorphology 145–146, 115–122.
Contents lists available at SciVerse ScienceDirect
Geomorphology journal homepage: www.elsevier.com/locate/geomorph
Discussion: Comparison of slope instability screening tools following a large storm event and application to forest management and policy Susan Shaw ⁎ Weyerhaeuser Company, P.O. Box 275, Springfield, OR 97477, United States
a r t i c l e
i n f o
Article history: Received 5 September 2012 Accepted 26 October 2012 Available online 22 November 2012 Keywords: Landslide Slope stability model Geographic information system (GIS) Forestry
a b s t r a c t The purpose of this discussion paper is to identify major technical errors made by Whittaker and McShane (2012) regarding the development and use of SLPSTAB (Shaw and Vaugeois, 1999; Vaugeois, 2000). SLPSTAB is a GIS-based data layer currently utilized as a regulatory tool for preliminarily screening slope stability potential on nonfederal, commercial timberlands in Washington State. © 2012 Elsevier B.V. All rights reserved.
Whittaker and McShane (2012) make several references to methods used to develop the SLPSTAB data layer. SLPSTAB currently is used by the Washington Department of Natural Resources (WDNR) as a preliminary screen of shallow landslide potential during its regulatory reviews of applications for proposed forest practices on nonfederal, commercial forestlands in western Washington, USA. As coauthor of Shaw and Vaugeois (1999) and codeveloper of SLPSTAB with Laura Vaugeois (deceased), I would like to correct several errors made in the paper by Whittaker and McShane (2012) regarding the data and models employed in creating the SLPSTAB screening tool and the intended use of this geographic information system (GIS) raster data set. First, Whittaker and McShane (2012) cite the WDNR GIS metadata file describing SLPSTAB (Vaugeois, 2000) that refers to the use of two models, SMORPH and SHALSTAB, in generating the SLPSTAB data layer. The current SLPSTAB grid layer (WDNR, 2007), however, was generated solely with the SMORPH model (Shaw and Johnson, 1995), which does not use climatic- or soil-parameter data explicitly in any aspect of its derivation or calibration. The SHALSTAB model (Montgomery and Dietrich, 1994) does employ these types of data and had we actually used this model in creating the SLPSTAB data layer, the Whittaker and McShane (2012) discussion regarding the benefits of more refined precipitation and soil-property algorithms would be relevant. Second, the reference to SHALSTAB in the GIS metadata file was intended as a placeholder for potential future data layer expansions but not necessarily as an indication of its use in the current version of SLPSTAB. As described in Shaw and Vaugeois (1999), statistically based comparisons of SMORPH and SHALSTAB landslide-probability distributions indicated that either model would work equally well ⁎ Tel.: +1 541 974 7805; fax: +1 541 988 0611. E-mail address: [email protected]. 0169-555X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.geomorph.2012.10.027
scientifically as a regulatory preliminary screening tool. The WDNR and the Washington Cooperative Monitoring, Evaluation, and Research Committee ultimately recommended to the Washington Forest Practices Board that the first version of the SLPSTAB layer be created using the SMORPH model because, unlike SHALSTAB at the time, this model (1) yielded output in terms of the regulatory decision-matrix criteria already established in Chapter 222-22(2)(iv) of the Washington Administrative Code (WAC; Washington Forest Practices Board, 2012a); (2) required no precipitation or soil-property rules to run; and (3) could be deployed immediately without modification to meet the mandates of Washington Engrossed Substitute House Bill 2091 and the Washington Forest and Fish Report (USDI et al., 1999). In addition, Shaw and Vaugeois (1999) found that the SHALSTAB model output was sensitive to the values of soil-property and hydrology input parameters, thereby making it challenging to assign input values representative of the large spatial and temporal variability in precipitation regimes and soil characteristics encountered at the regional (i.e., western Washington) scale. Notwithstanding, the SHALSTAB placeholder was preserved to accommodate the future use of this model, should the model authors elect to address these applied-management issues. Third, the SLPSTAB layer was created with a model designed to predict shallow-landslide potential and was calibrated solely with shallow landslide inventories (Shaw and Vaugeois, 1999; Vaugeois, unpublished document). Hence, SLPSTAB was not intended to be used in comparing model predictions of landslide potential with deep-seated or road-related landslide initiation points. The WDNR aerial-reconnaissance data used in Whittaker and McShane (2012) included all observed landslide types. Landslide type, however, is not listed in paper Section 2.1 as one of the criteria for sample selection. Whittaker and McShane (2012) would benefit from some clarification in this regard.
S. Shaw / Geomorphology 184 (2013) 154–155
Fourth, Washington State does not regulate forest practices on the basis of the SLPSTAB screening tool, in part because of data resolution issues associated with the digital elevation model (DEM) from which the tool is derived. The purpose of the SLPSTAB screening tool in a regulatory context, as described by Vaugeois and Shaw (2000), is to trigger a site geotechnical investigation by a qualified expert (Washington Forest Practices Board, 2012b) of any proposed forest practice that would occur on or within the vicinity of ground identified as potentially unstable by the data layer. SLPSTAB is not capable of pinpointing the exact location of existing and potential landslide initiation points because of horizontal and vertical inaccuracies in the DEM data. Most of the current SLPSTAB layer was produced using USGS 10-m DEM with a horizontal accuracy on the order of ±10.7 m (35 ft) (Vaugeois, 2000). Consequently, a grid cell representing a ‘high’ or ‘medium’ landslide probability rating could be offset spatially from an actual landslide initiation point, and limiting forest practices in that grid cell could result in misapplied ground protection (e.g., potentially not protecting the actual failure site). In the absence of any other field-verified site information, allowing the ‘high’ or ‘medium’ landslide-potential rating for any given grid cell to dictate the forest-practices classification or management prescription for the actual slope area represented by that cell would be counter to the purpose of SLPSTAB as stated in Vaugeois (2000). Furthermore, identifying the exact location of potential or existing landslide initiation points presently is beyond the capability of DEM-based topographic models where high resolution, LiDAR-derived DEM are not yet available (i.e., the majority of Washington commercial timberlands in steep, mountainous terrain). References Montgomery, D.R., Dietrich, W.E., 1994. A physically-based model for the topographic control on shallow landsliding. Water Resources Research 30, 1153–1171. Shaw, S.C., Johnson, D.A., 1995. Slope morphology model derived from digital elevation data. Proceedings, 1995 Northwest Arc/Info Users Conference, Oct. 23–25, Coeur d'Alene, ID (13 pp.).
155
Shaw, S.C., Vaugeois, L.M., 1999. Comparison of GIS-based Models of Shallow Landsliding for Application to Watershed Management. TFW-PR 10-99-001, #118 Washington Department of Natural Resources, Olympia, WA. (Available from: http://www.dnr. wa.gov/Publications/fp_tfw_pr10_99_001.pdf. Accessed 27 March 2012). U.S. Department of Interior (USDI) Fish and Wildlife Service, U.S. Department of Commerce National Oceanic and Atmospheric Administration, U.S. Environmental Protection Agency, Office of the Governor of the State of Washington, Washington Department of Natural Resources, Washington Department of Fish and Wildlife, Washington Department of Ecology, Washington State Association of Counties, Washington Forest Protection Association, Washington Farm Forestry Association, Colville Confederated Tribes, and other tribal governments, 1999. Forests and Fish Report. Prepared for the Washington Forest Practices Board and the Governor's Salmon Recovery Office. Washington Department of Natural Resources, Olympia, WA. (218 pp. Available from: http://www.dnr.wa.gov/BusinessPermits/Topics/ForestPracticesRules/Pages/fp_ffr.aspx. Accessed 27 March 2012). Vaugeois, L.M., 2000. SLPSTAB: modeled slope stability screen. Prepared by the Washington Department of Natural Resources, Olympia, WA. (Available from: (http://www.dnr.wa.gov/BusinessPermits/Topics/ForestPracticesApplications/Pages/ fp_gis_spatial_data.aspx) or (http://www.dnr.wa.gov/Publications/fp_data_slpstab_ meta.html). Accessed 27 March 2012). Vaugeois, L.M., unpublished document. Protocols Used for Developing the SLPSTAB Dataset in Western Washington. Archived by Washington Department of Natural Resources, Olympia, WA. Available from Leslie Lingley, Science Team Leader, Forest Practices Division, Washington Department of Natural Resources, Olympia, WA ([email protected]). Vaugeois, L.M., Shaw, S.C., 2000. Modeling shallow landslide potential for watershed management. 2000 ESRI User Conference Proceedings (Available from: http://proceedings. esri.com/library/userconf/proc00/professional/papers/PAP310/p310.htm. Accessed 27 March 2012). Washington Department of Natural Resources (WDNR), 2007. Forest practices application review system. Available from: http://fortress.wa.gov/dnr/app1/fpars/viewer. htm(Accessed 27 March 2012). Washington Forest Practices Board, 2012a. Title 222 WAC – forest practices rules, chapter 222-22 – watershed analysis. Available from: http://www.dnr.wa.gov/ Publications/fp_rules_ch222-22wac.pdf (Accessed 27 March 2012). Washington Forest Practices Board, 2012b. Title 222 WAC – forest practices rules, chapter 222-10 WAC – State Environmental Policy Act Guidelines. Available from: http:// www.dnr.wa.gov/Publications/fp_rules_ch222-10wac.pdf (Accessed 27 March 2012). Whittaker, K.A., McShane, D., 2012. Comparison of slope instability screening tools following a large storm event and application to forest management and policy. Geomorphology 145–146, 115–122.