Geomorphology. ▪ Landforms and geology can be more important here than buffer width. For example, in the San Xxxx Islands, there can be a 45° slope on basalt form that can be very stable. ▪ Geomorphic shore form is an important consideration – geologic legacy, landscape position, density, slope, etc. Use of Xxxxxxx (2008) geomorphic classification system may be useful (Appendix F). Soil and Vegetation ▪ Riparian areas can increase slope stability (through root structure) and increase water interception and absorption. Protecting natural rates of sediment delivery and protecting processes and functions of nearshore ecosystems may be achieved by establishing and maintaining adequate riparian buffers. ▪ Upslope alterations can be contributing factors to slope instability. ▪ It is important to consider flow paths; for example, slope stability may be associated more with altered upland drainage patterns or precipitation patterns. Buffer width versus landform may be the most important factor. For example, steeper slopes, particularly those with underlying geologic instability, require wider buffers. Table 6. Setback distances (in ft) from Xxxxxx et al 1992 as cited in Xxxxxxxxx and Xxxxx (1994) for different bluff heights at various levels of stability where geologic stability for 50-years cannot be demonstrated. Bluff Height (ft) Stable (1:1)(450) Moderately Stable (2:1)(300) Unstable (1:1)(450)+ (2:1)(300) 20 20 40 60 40 40 80 120 60 60 120 180 80 80 160 240 100 100 200 300 120 120 240 360 140 140 280 420 160 160 320 480 180 180 360 540 200 200 400 600 Figure 6. Construction setbacks for different bluff heights at various levels of stability, where geologic stability for 50-years cannot be demonstrated (after Xxxxxx et al 1992 as cited in Xxxxxxxxx and Xxxxx 1994).
Geomorphology. The Snake River is a braided gravel-bed river increasing in gradient from 0.0007 between JLD and Pacific Creek to 0.0038 between Schwabachers Landing and Moose (Figure 2-2, Chapter 2 in Xxxxxx, 2007). Xxxxx (1991) and Xxxxxxx et al. (2005) investigated geomorphic change in the same study area and determined that total sinuosity, their surrogate metric for channel stability, increased over time and was greatest below tributaries and in wide alluvial valleys. They attributed greater channel activity below tributaries to the inability of lower-magnitude floods to mobilize the delivered sediment load (Xxxxxxx et al., 2005). Xxxxxx (2007) analyzed four series of aerial photographs from 1945, 1969, 1990/1991, and 2002 in an improved GIS, arguing that the Snake River channel has remained active throughout the study area since 1945, though the majority of channel activity was concentrated in the unstable reaches with multi-thread channels (Chapter 2 in Xxxxxx, 2007). Increased deposition and channel narrowing occurred during periods of relatively low-magnitude annual floods, from 1945 to 1969, while erosion and channel widening occurred during periods of higher-magnitude annual floods, from 1969 to 1990/1991 and from 1990/1991 to 2002 (Chapter 2 in Xxxxxx, 2007). Channel activity and changes in channel width occurred in reaches both proximal and distal to tributaries. Xxxxxx (2007) argued that, although the channel and floodplain form may have been affected following the flow regime change in 1958, the Snake River has recovered, remains active through most of GTNP, and is capable of mobilizing portions of the bed downstream from tributaries (Chapter 2 in Xxxxxx, 2007).
Geomorphology. During the Class III surveys, in areas within the Project APEs for direct effects, a qualified archaeologist with professional experience in geomorphological analysis will assess the potential for buried cultural materials in areas that will be impacted by construction of any GWD Project facility or other planned excavation deeper than two feet. The assessment will attempt to identify areas that contain thick sequences of post-14,000 B.P. deposits that are of a suitable geologic character to bury and preserve cultural zones and thick enough to hide any surface evidence, considering geomorphological evidence and other surface indicators. If the qualified archaeologist determines that a given area showed indication of a high likelihood of buried significant cultural deposits, the archaeologist will make recommendations to the BLM for additional geomorphological evaluation, or archaeological testing, as may be reasonably indicated. The BLM, in consultation with the SHPO, will determine if additional geomorphological evaluation or archaeological testing is warranted.
Geomorphology. To supplement what is said in the Survey and Report Guidelines about this, you must check for buried deposits on floodplains of ALL major rivers where floodplains are over 1/2 mile wide. You of course do not have to do this in disturbed areas or in naturally low areas such as sloughs, abandoned channels, and wetland, but should document these conditions by map or reference to geological report. Remember to check for loess fall buried sites too, especially in the western counties.
Geomorphology. Durin g the Clas s III survey s, in areas within the P roject APEs for direct ef fects, a qualified archaeologist wi th professional experience in geom orphological analysis will assess th e potential f or buried cultural m aterials in are as that will be impacted by construction of any GWD Project f acility or other planned excavation deeper than two feet. The assessment will attem pt to identify areas that contain thick sequences of post-14,000 B.P. deposits that are of a suitable geologic character to bury and preserve cultural zones and thick enough to hide any surface evidence, consideri ng geomorphological evidence and other surface indicators. If the qualif ied arch aeologist determines that a given area showed indication of a high lik elihood of buried s ignificant cultura l depos its, the archaeologist will m ake recommendations to the BLM for additional ge omorphological evaluation, or archaeological testing, as m ay be reasonably ind icated. Th e BLM, in consultatio n with the SHPO, will determine if additional geomorphological evaluation or archaeological testing is warranted.
