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HomeMy WebLinkAboutSUS248S1REAM CHANNEL CLASSIFICATION USING LARGE SCALE AERIAL PHHOGRAPHY FOR SOUTHEAST ALASKA WA TERSHED MANAGEMENT Steven J. Paustian, Daniel A. Marion, and Daniel F. Kelliher, Tongass National Forest-Chatham Area P.O. Box 1980, Sitka, AK 99835 ABS1RACT Stream channel management units called channel types have been identified using stream morphologie and landform characteristics. Channel types have been mapped for approximately 800,000ha of Chichagof Island in Southeast Alaska. Techniques are described for using mapping differentia to distinguish and map channel types on 1:15,840 scale color aerial photographs. Channel types provide a framework for making aquatic resource management interpretations at various forest planning levels. A current application to a timber sale project plan is described. INVENTORY PURFOSE The need for a reliable watershed and stream inventory in Southeast Alaska arase with the rapid development of timber resources in conjunction with increasing pressure on natural fish production from commercial, subsistence, and sports fishermen. Timber harvesting and fishing are not always fully compatible resource uses. Sail erosion and subsequent sedimentation from logging has the potential to reduce fish spawning and rearing habitat quality. Streamside canopy removal may also affect stream temperature, food sources, and large organic debris (LOD-tree stems greater than !Ocm in diameter) that influence fish habitat quality and channel stability (Chamberlin 1982). These potential timber harvesting impacts on highly productive fish habitat are a major forest management issue in the region. An aquatic resource inventory has been developed on the Tongass National Forest-Chatham Area (TNF-CA) to provide a means for addressing this resource issue. In addition, ether resource issues such as maintenance of water quality and design of inchannel structures (e.g., bridges, fish passes) are addressed. This reconnaissance leve! inventory procedure is intended for forest resource planning applications. On the bread forest land use planning leve!, it provides general aquatic resource information applicable to the development of national and regional forest management direction. For specifie project planning applications, aquatic resource inventory data is used to make preliminary fish habitat quality and habitat sensitivity management interpretations on identifiable stream segments. These channel type management interpretations are categorizations of a given channel area according to a management concern, problem, or constraint encountered in conducting a given management activity. The remoteness, difficulty of access, and large size of the survey area make detailed ground surveys of streams impractical. Channel type mapping combined with a systematic field sampling scheme, provides a reliable, cast effective, and efficient method for TNF-CA stream inventories. ' 670 SET TING The area inventoried enco~asses approximately 800,000ha of the TNF-CA on Chichagof Island, located between Juneau and Sitka, Alaska (figure 1). The climate is maritime, with annual precipitation ranging between 200 and 450cm. Vegetation is predominantly western hemlock -Sitka spruce rain forest with interspersed muskeg bogs composed primarily of sphagnum masses and sedges. These vegetation communities grade to subalpine brush fields and alpine tundra at elevations between 500 and 700m. Streams draining Chichagof Island commonly occupy glaciated valleys. Runoff originates in alpine snowfields or small cirque lakes and descends rapidly to the many fiords and inlets that dissect the archipelago. "/~ • 1 ~ s'" ' ~ p.,Lil. (__,.< i ?~> "' ' c·:--::----1. ',_.;-~,~~' ~): MGç. A••ottii'f'l_ -- Figure 1. SE Alaska and Chichagof Island survey area. THEORY AND APFROACH The TNF-CA Aquatic Resource Inventory is a combination of channel classification, channel type mapping, and field data collection. Classification is the determination of channel characteristics that distinguish channels areas of similar forest management. interpretations (see "Channel Type ~scriptions" in USDA Forest Service Alaska Region l983a, for a complete discussion of classification characteristics). Channel type mapping is the use of differentia to locate channel types using 1:15,840 color aerial photographs. Differentia are certain channel characteristics that can be inferred from aerial photographs. They are also characteristics that are correlated to the other, nonobservable channel classification characteristics such as bed substrate size. Field data collection is used to make observations on all classification characteristics so as to determine the specifie management interpretations associated with each channel type. The TNF-CA Channel Type Classification System (CTCS) is based on three concepts. First, geomorphic processes that are independent of inchannel processes affect stream channel characteristics. Watershed geomorphic factors directly or indirectly influence: streamflow characteristics; chemical and physical water quality characteristics; and stream channel size, shape, and substrate characteristics (Beschta 1978). In aggrêgate these stream characteristics represent the physical surroundings or habitat of aquatic organisms. The relationship of these geomorphic variables to fish habitat has been supported by several investigators. Platts (1979) demonstrated the relationship of stream arder to the distribution of fish populations in Idaho river basins. Swanston et al. (1977) used quantitative geomorphic variables to qualitatively differentiate between good and poor pink and chum salmon producing streams in Southeast Alaska. Parsons et al. (1981) showed significant correlation between geo- morphic parameters and fish habitat quality in Oregon salmon streams. 671 The second concept is that fluvial processes within a drainage network affect inchannel characteristics and fish habitat quality. Schumm (1979) describes three fluvial system zones according ta their dominant function: sediment source, transport, and deposition zones. Physical stream channel characteristics and associated aquatic habitat are largely dependent upon the dominant fluvial process shaping them. In the source zone (high gradient, lst arder channels) high velocity streamflow, and active channel erosion, and sediment transport precludes the development of stable, diverse aquatic habitat. At the other end of the spectrum more consistent streamflow and sediment transport characteristics of deposition zone channels (law gradient, 3rd arder channels) promotes the establishment of more diverse and productive aquatic communities. The third concept is that riparian functions within a channel area affect fish habitat quality. Riparian zone function has been described by Meehan et al. (1977) and Swanson et al. (1981) in terms of the role stream side vegetation canopy, stems, roots, and inchannel LOD play in shaping aquatic habitat. Streamside canopy shading influences primary food production by reducing photosynthetic rates and overall rates of biological activity. Riparian vegetation also controls the availability of organic detritus as a basic food source for aquatic organisms. Tree roots and law lying brush in-- crease stream bank stability; provide undercut banks for fish caver; and retard the movement of sediment and water during flood flows. Inchannel LOD helps ta shape the distribution of pool, riffle, and undercut bank habitat. It also acts as a trap for fine particulate organic matter and serves as a substrate for biological activity. The CTCS is a hierarchical approach in which channel types are components of larger hydrologie groupings of drainage segments within watersheds. The first level of classification for management interpretation is made using subsections. Subsections are physiographic regions having different climate, geology, and topography (USDA Forest Service, Alaska Region l983b). Subsections are used ta first group watersheds according ta broad regional trends in water quality and channel stability. The TNF-CA is divided into 16 subsections, each approximately 175,000ha in size. Information from past TNF-CA water resource inventories indicates that subsection boundaries separate watersheds with significantly different water chemistry characteristics. In addition, though the same channel types occur in each subsection, they can have important differences in fish habitat quality and sediment regime characteristics. The next level in the classification hierarchy is the channel type association. Channel type associations are defined by the dominant fluvial geomorphic processes influencing the development of stream environments. Channel type associations are segregated by their dominant fluvial functional zones of sediment source (A association), transport (B association), and deposition (C association). Factors important in this categorization include: contributing watershed area, relief, and stream arder. Individuel channel types within each association are differentiated by adjacent landforms, channel morphology, and riparian vegetation communities. The average lengths of channel types are 1200m, 1800m, and 2200m for the A, B, and C associations respectively. Each channel type has a relatively consistent range of fish habitat and channel stability character- istics. Consequently, for forest planning pu~oses, a specifie set of management interpretations is applicable ta a given channel type. 672 Table l. Selected Olannel Type Mapping Differentia, 1NF -CA Channel Adj ace~ Channel Basin Type Landform( s)l Characteristics2 Area3 Al Subalpine sideslopes, -Very high gradient Small mountain s lapes, -Deep incision hills, gently -Narrow width sloping lowlands -Single channel ClA Flood plain -Law gradient Modera te -Shallow incision to large C3A Mountain slopes, hills, infrequently -Moderate width -t-'ultiple channels -Moderate gradient Large ta -Moderate incision very large dissected footslopes, -Moderate width frequently dissected -Single channel f ùotslopes and alluvial fans SOUR:E: USDA Forest Service Alaska Region 1983a. ~~~~~x Moderate ta high Law ta modera te Modera te NOTE: All feature interpretations are made using 1977 1:15,840 co lor aerial photographs. 1. Landforms are defined according to the Chatham Area "Integrated Resource lnventory Landform Descriptive Legend" (USDA Forest Service Alaska Region l983b). 2. Channel incision ranks: shallow = less than 3m; moderate = 3m ta lOm; deep = lOm to 30m; very deep = greater than 30m. Channel gradient ranks: law = less th an 3%; modera te = 3% ta 6%; high = 6% ta 10%; very high = greater than 10%. Channel pattern classes: Single channels have one continuous main channel bed; multiple channels have a main channel bed that is frequently broken by overflow channels or islands; braided channels have numerous, interlaced channels and extensive gravel bar development. Channel width ranks: narrow = less th an lOm; modera te = lDm ta 30m; bread = greater th an 30m. 3. Basin are a classes: small = less than 50Cl1a; modera te = 50Clla ta l30Cl1a; large = l30Clla ta 390Clla; very large = greater than 3900ha. 4. Canùpy caver classes: law = less than 25%; moderate = 25% ta 50%; hi !tl = grea ter th an 50%. CHANNEL TYPE MAPPING PROCEDURE The mapping differentia used to locate channel types on 1:15,840 aerial photographs are listed in table l. Adjacent landform and basin area are characteristics that account for geomorphic processes acting outside of the stream channel proper which affect channel characteristics. Actual channel characteristics used as differentia are channel gradient, incision depth, width, and pattern. These characteristics account for inchannel fluvial processes which affect channel characteristics. Canopy caver reflects riparian functions which affect fish habitat quality. All of these differentia are correlated to, and reflect, channel characteristics affecting channel type management interpretations. The differentia subdivisions defined in table l are the breaks in these differentia determined to be significant in making channel type management interpretations. 673 Adjacent landform refers to the landform type that occurs directly adjacent to the channel area. Landforms are defined according to the TNF -CA "Landform Descriptive Lege nd" in Integrated Re source Inventory: Legends Handbook II (USDA Forest Service, Alaska Region 1983b). In certain cases, only a single landform is associated with a given channel type, whereas in other cases, there is a group of landforms. Limited inclusions of other landforms not defined as being associated with a channel type are also possible, but must meet inclusion rules defined for each channel type (USDA Forest Service, Alaska Region l983a). Adjacent landform influences channel bank stability and sediment delivery to the the channel. Landforms are primarily classified by slope shape and gradient, ex- ternal relief, drainage dissection frequency, and dissection depth. Drainage dissection frequency and slope shape (e.g., concave, convex, straight, or flat) are directly observable from features on the aerial photographs. Dissection depth is estimated using observable tree heights for comparison. External relief represents the range in landform elevation and is measured from 1:63,360, lOO feet contour interval topographie maps until the intrepreter is sufficiently experienced to estimate it directly from the aerial photographs. Basin area is the catchment size of a given channel type. Peak and base flow magnitudes are strongly influenced by basin area. It is measured from aerial photographs using a transparent dot grid overlay. Channel characteristics includes four criteria: channel gradient, incision depth, width, and pattern. Channel gradient is the channel bed slope. It greatly influences channel stability, stream power, and fish passage. Using aerial photographs, gradient is inferred from the adjacent landform slope or by the relative frequency of cascades, and gravel bars (the steeper the gradient, the more fre- quent are cascades, and the less frequent are observable gravel bars). Incision depth is the vertical distance from the channel bed to the nearest observable slope break above the lower stream bank. Incision depth influences bridge crossing design and channel flow contain- ment. It is estimated by making comparisons to nearby trees of known heights. Channel width is defined as the horizontal distance between opposing high water marks (i.e., bankfull stage). Channel width influences stream crossing design and indicated peak flow magnitudes. It is measured directly from aerial photos using a scale conversion factor. Channel pattern is a description of the main channel bed continuity. It reflects flooding and sediment routing characteristics, flow containment, channel stability, and fish habitat characteristics. The aerial photograph features used to distinguish channel patterns are listed in footnote 2 of table 1. Canopy caver is defined as the percent of shading provided during the annual peak insolation period (July for the TNF-CA). It affects stream temperature extremes, dissolved oxygen content, riparian vegetation cover, and organic inputs to the aquatic environment. Channel type canopy caver characteristics are described using typical groupings of canopy classes defined for adjacent landtype mapping units (USDA Forest Service, Alaska Region 1983~). Crown density is measured from aerial photos using a crown closure comparator overlay. 674 Figure 2. An example of three Tongass National Forest, Chatham Area channel types on a 1:15,840 scale stereo photograph pair. Color aerial photography generally permit better distinction of incision depth and grave! bars. An example of channel type mapping is shawn in figure 2. Continuous chutes and falls and the lack of observable grave! bars are indicative of very high gradients. These features are apparent in the Al channel type in figure 2. A moderate overall gradient is inferred for the C3A channel type because observable falls and chutes are lacking, but so are observable grave! bars. The ClA channel type also lacks falls and chutes, but has obvious grave! bar development. This is characteristic of a law channel gradient. Channel width differences are clearly apparent between the Al (less than !Om) and either the C3A or ClA (!Om to !Sm) channel types. Adjacent landform differences are also apparent between the ClA (flood plain adjacent) and either the Al or C3A (combination of subalpine sideslopes and mountain slopes adjacent) channel types. The actual channel type mapping procedure is divided into three parts: premapping, field sampling, and final mapping. Premapping is the initial differentiation and mapping of channel types as described above. Field sampling is the ground truthing of the channel type mapping and collection of additional resource data for making management interpretations. Final mapping entails mapping corrections, channel type correlation, and mapping transfer to the final map base. Incorrectly mapped channel types are reexamined on the aerial photographs to determine the interpretation error. Correlation is performed once al! watersheds are mapped to consolidate those channel types with insignificant management interpretation differences, or to eliminate those channel types that occur infrequently. The final map product is to be 1:31,680 topographie quadrangle maps. APPLICATIONS Channel type classification and inventory using aerial photographs is a framework within which aquatic resource information can be collected, compiled, mapped, and applied in a systematic manner. Each channel type represents a distinct range of aquatic resource characteristics and management concerns. Intensively field sampling al! streams is generally not a practical approach for the management of extensive land areas such as the TNF-CA. Channel types serve as a basis for extrapolating stream field data to unsurveyed areas with a 675 reasonable degree of confidence. Channel type maps also provide a means for aggregating stream survey information. By accumulating lengths of channel types, for example, a relative measure of the total amount of fish habitat classes found within a watershed or subsection can be obtained. Two levels of classification and inventory have been mentioned. The first leve!, represented by TNF-CA subsection delineations, pertains to very general resource management applications. The second leve! defined by channel types is applicable to more detailed project plan- ning needs. The project planning applications of the channel type classification will be elaborated upon in the following discussion. Channel type mapping was used in the evaluation of proposed resource management alternatives for the Alaska Lumber and Pulp 1986-90 Operating Plan Draft Environmental Impact Statement (USDA Forest Service, Alaska Region 1983c). For this application each channel type was assigned an aquatic resource value rating based on channel sensitivity and fish habitat quality indices. Channel sensitivity factors include: sediment input and conveyance potential; riparian vegetation influence; and large organic debris (LOD) influence. Sediment related factors are derived from channel bank and bed stability and stream power measurements. Riparian vegetation and LOD influences are based on streamside canopy type and closure, and the distribution and stability of natural inchannel LOD accumulations. The habitat quality index is a dimensionless number derived from empirical equations relating fish populations to physical habitat characteristics (Barber, Oswood, and Deschermeier 1981). These habi- tat features are defined by spawning grave! area, instream debris, riparian caver, and water depth and velocity classes. The product of the channel type sensitivity index, the habitat quality index, and the channel type length yields the aquatic value rating (AVR). In its present form the AVR is not a measure of fish biomass production. The AVR is a relative measure of stream value. The rating is based on the extent and quality of the fish habitat the stream contains; as modified by the streams sensitivity to change from management disturbances. Color coded stream resource maps developed from AVR habitat quality and sensitivity classes provided planners with a visual display for locating potential management conflict areas and evaluating possible consequences of management alternatives. For example, channel types coded red on the aquatic resource map rank high in habitat quality and sensitivity rating. Those stream segments may then be avoided in planning timber cutting units. Where potential conflicts cannat be avoided, those conflict areas can be prioritized by resource specialists for on-site review and the development of activity mitigation prescriptions. SUMMARY Stream channels can be classified using aerial photo differentia according to their morphological, biological, and management response attributes. The systematic process of classification and mapping provides the basis for identification of homogeneous stream and channel adjacent units called channel types. Channel types represent a definable mapping unit for data collection, land management planning, and management activity prescriptions relating to aquatic stream resources. 676 REFERENCES Chamberlin, T. W., 1982, "Influence of Forest and Range land Management on Anadromo~ Fish Habitat in Western North America: Timber Harvest," USDA Forest Service, General Technical Report A'IW-136 Barber, w. E., M. w. Oswood, and S. Deschermeier, 1981, Validation of Two Habitat Fish Stream Survey Techniques: The Area and Transect Methods. Final report for USDA Forest Service, Contract No. 53-0109-0-00054, Juneau, Alaska Beschta, R. L. , 1978, "Inventory ing Small Streams and Channels on w ildland Watershed s." In: Proc. National Workshop on In te grated Inventories of Renewable Natural Resources, Jan. 8-12, 1978, Tucson, Ariz., USDA Forest Service, Gen. Tech. Report RM-55. pp. 104-113 Meehan, w. R., F. J. Swanson, J. R. Sedell, 1977, "Influences of Riparian ~getation on Aquatic Ecosystems with Particular Reference to Salmonid Fishes and their Food Supply," In: Symposium on the Importance, Presentation and Management of the Riparian Habitat, July 9, 1977, Tuscon, Arizona. pp. 137-145 Parsons, M. G., J. R. Maxwell, and D. Heller, 1981, "A Predictive Fish Habitat Index Madel Using Geomorphic Parameters," In: N. B. Armantrout, editor, Acquisition and Utilization of Aguatic Habitat Information, pp. 85-91, Symposium Proceeding of the American Fisheries Society, Western Section Platts, W. S. 1979, "Relationships Among Stream Orders, Fish Populations, and Aquatic Geomorphology in an Idaho Ri ver Drainage," Fisheries, Vol. 4, No. 2, pp. 5-9 Strahler, A. N., 1957, "QJantitative Analysis of Watershed Geomo:q::Jhology." American Geomphysical Union, Transactions: Vol. 38, pp. 913-920 Swanson, F. J., S. V. Gregory, J. R. Sedell, and A. G. Cambell, 1982, "Land-Water Interaction: The Riparian Zone" In: R. L. Edmonds, editor, Analysis of Coniferous Forest Ecosystems in the Western United States, US/IBP Synthesis Series 14, pp. 267-291, Hutchinson Ross Publishing Swanston, S. N., W. R., Meehan, J. A. Md'lutt, 1977, "A Quantitative Geomorphic Approach to Predicting Productivity of Pink and Chum Salmon Streams in Southeast Alaska," USDA Forest Service Research Paper PNW-227 USDA Forest Service, Alaska Region, 1983a, "Tongass National Forest - Chatham Area Aquatic Resource Inventory Handbook:" unpublished report on file at the Chatham Area Supervisor's Office, Sitka, AK pp. VIII-! to VIII-105 , 1983b, "Tongass National Forest - Chatham Are a Integrated Re source Inventory: Legends Handbook II:" unpublished report on file at the Chatham Area Supervisor's Office, Sitka, AK, pp. 1-130. , 1983c, "Alaska Lumber and Pulp 1986-90 Operating Plan Draft Environmental Impact Statement, in press 677 This document is copyrighted material. Permission for online posting was granted to Alaska Resources Library and Information Services (ARLIS) by the copyright holder. Permission to post was received via e-mail by Celia Rozen, Collection Development Coordinator, on September 4, 2013, from Matthew Austin, Publications Production Assistant, American Society of Photogrammetry and Remote Sensing. This article is identified as SUS 248 in the Arctic Environmental Institute Susitna Aquatic Impact Assessment Project Bibliography (1986), compiled by Arctic Environmental Information and Data Center (AEIDC). RENEWABLE RESOURCES MANAGEMENT Applications of Remote Sensing Proceedings of the RNRF Symposium on the Application of Remote Sensing to Resource Management Seattle, Washington May 22-27, 1983 Sponsored by American Society of Photogrammetry In Cooperation with the Renewable Natural Resources Foundation Under the auspices of Commission VII, International Society for Photogrammetry and Remote Sensing