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2009-08-24_REVISION - C1982056 (4)
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2009-08-24_REVISION - C1982056 (4)
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Last modified
8/24/2016 3:55:01 PM
Creation date
8/25/2009 1:24:41 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1982056
IBM Index Class Name
Revision
Doc Date
8/24/2009
Doc Name
Sage Creek Subsidence Project Cultural Resources Inventory
From
MAC Metcalf Archaeological Consultants, Inc
To
BLM
Type & Sequence
PR8
Email Name
JHB
Media Type
D
Archive
No
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subsidence area will see some changes in gradient and pooling in certain areas. These situations are <br />allowed to resolve over time naturally; the mine operator will not be modifying stream channels or <br />undertaking other surface disturbing activities in response to stream alterations. It is anticipated that <br />over the course of several years following the subsidence, natural drainages will revert to a condition <br />of dynamic equilibrium, with pools filling in with sediment, and high points eventually eroding <br />down to the base gradient.of the stream at that point (see NSW DPI 2006 for a discussion of <br />subsidence effects). <br />Potential Effects to Cultural Resources <br />Although the potential effects of subsidence on archaeological sites has been considered for <br />a number of longwall mining projects in the United States, Great Britain, and Australia, frustratingly <br />little is published on the actual effects. Most approval documents for longwall mines include some <br />level of field inventory, recording, site avoidance, data recovery, and pre- and post-subsidence <br />monitoring (e.g. MOA, Manti-LaSal National Forest, Canyon Fuel SUFCO Mine Plan [Manti-LaSal <br />National Forest 2000]). However, no results from actual post-subsidence monitoring could be found <br />in the literature. <br />Based on a literature review, archaeologists have mainly focused on the effects of subsidence <br />in coastal regions (e.g., Gagliano 1984). For example, Lewis (2000) examined this effect to sites <br />along the Mississippi Gulf Coast. He identified two types of processes. Exogenic subsidence is <br />caused by geologic processes near the earth's surface, processes that can cause the sinking of <br />individual loads and the burial of older components. Along the Gulf Coast the most common source <br />of this process is the removal of fluids through oil and gas extraction. Endogenic subsidence is <br />caused by deep earth geologic processes, such as faulting. <br />The Lewis study focused on examination of geologic factors biasing site distribution along <br />low-energy coast-line. The results provide some insight into how subsidence from the removal of <br />near-surface oil and gas deposits can increase erosion and destruction of archaeological deposits, <br />as well as biasing the evidence of site distribution. More relevant is work conducted as part of the <br />Moolarben Coal Project, a long wall coal mining project in the Western Coal Fields of New South <br />Wales, Australia (Hamm 2006). The results from this survey are largely descriptive and intuitive. <br />For example, archaeological sites with the highest risks involve standing sandstone structures, <br />rockshelters, or sandstone outcrops and associated drainages. In addition to site salvage and test <br />excavations, further recommendations involve on-going monitoring and assessment of subsidence <br />impacts. <br />In the trade journal primefacts (NSW DPI 2006), the authors report that extraction of coal <br />may cause overlying sediments to move three-dimensionally at a given point potentially resulting <br />in vertical as well as horizontal movement of sediments. For Sage Creek, understanding the effect <br />of subsidence on open, stratified hunter-gather sites is largely unknown. Likely impacts such as <br />erosion of sites within alluvial terraces can result from the increased grade of drainages and surface <br />slope. <br />Applying this to the Sage Creek project, it is recognized that some environments are subject <br />to alteration through subsidence-cliffs, water bodies, and springs for example, but flat-lying or <br />undulating terrain is generally lowered gradually with few or no shear planes affecting surface <br />13
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