Groundwater sapping channels: Summary of effects of experiments with varied stratigraphy

Experiments in the recirculating flume sapping box have modeled valley formation by groundwater sapping processes in a number of settings. The effects of the following parameters on sapping channel morphology were examined: surface slope; stratigraphic variations in permeability cohesion and dip; and structure of joints and dikes. These kinds of modeling experiments are particularly good for: testing concepts; developing a suite of distinctive morphologies and morphometries indicative of sapping; helping to relate process to morphology; and providing data necessary to assess the relative importance of runoff, sapping, and mass wasting processes on channel development. The observations from the flume systems can be used to help interpret features observed in terrestrial and Martian settings where sapping processes are thought to have played an important role in the development of valley networks

Groundwater sapping valleys: Experimental studies, geological controls and implications to the interpretation of valley networks on Mars

An integrated approach using experimental laboratory models, field studies of terrestrial analogs, and remote studies of terrestrial field sites were applied to the goals of understanding the nature and morphology of valley networks formed by groundwater sapping. In spite of problems with scaling, the experimental studies provide valuable insights into concepts relating to the initiation, development, and evolution of valleys by groundwater sapping. These investigations are also aimed at developing geomorphic criteria for distinguishing valleys formed by surface runoff from those formed by groundwater sapping processes. Channels that were field classified as sapping vs. runoff were successfully distinguished using statistical analysis of their respective morphologies; therefore, it may be possible to use similar techniques to interpret channel genesis on Mars. The terrestrial and flume studies provide the ground truth dataset which can be used (and will be during the present year) to help interpret the genesis of valley networks on Mars

Sapping Features of the Colorado Plateau: a Comparative Planetary Geology Field Guide

This book is an attempt to determine geomorphic criteria to be used to distinguish between channels formed predominantly by sapping and seepage erosion and those formed principally by surface runoff processes. The geologic nature of the Colorado Plateau has resulted in geomorphic features that show similarities to some areas on Mars, especially certain valley networks within thick sandstone formations. Where spring sapping is an effective process, the valleys that develop are unique in terms of their morphology and network pattern

Post-Flood Cleanup Alternatives along Stream Corridors in Central Pennsylvania Helping Resolve River and Land Use Conflicts in an Economically and Ecologically Sustainable Manner

Report on managing river corridors of Central Pennsylvania in an economically and ecologically sustainable manner. Fluvial geomorphologists and civil engineers from Bucknell University present results of research and analysis of the impact of floods on Central Pennsylvania streams, bridges, dams, and roads. Ten sections cover 1. Key Concepts for Managing River Corridors in a Sustainable Manner; 2. Options for Managing the Conflict between Nature and Man; 3. The Physical Imperatives of River Systems; 4. Dynamic Equilibrium of Streams and Anticipating Adjustments in the Future; 5. The Conflict: Today’s Accounting; 6. Cost-Benefit Analysis; 7. Short vs. Long Term Solutions: A Choice of Management Scenarios; 8. “Stream-Cleaning” – allow gravel or “do nothing”? 9. Informing the Alternative Selection Process; 10. Managing Sustainably. The report focuses on the long term benefits of a geomorphic corridor management approach which can benefit both property owners and riparian ecosystems. The largest challenge is not in conducting the scientific analyses to determine the river’s slope and planform requirements, but rather in how to redefine the relationship of public and private investments with fluvial dynamics in an equitable manner over time within a watershed. The larger short term costs associated with using a geomorphic-based approach, where land conversion is necessary, become more acceptable and economically justifiable where channelization projects have failed repeatedly or in post flood remediation where major erosion, property damage, and channel avulsions have occurred. A passive geomorphic approach may be the most desirable alternative due to its lower maintenance costs but is highly dependent upon landowners willing to accept what may be significant changes in land use expectations. Concluding recommendations exhort State and Federal agencies involved with river resource management to work together to provide economic incentives and technical assistance for towns and landowners to make decisions that resolve immediate conflicts with the long term watershed solutions in mind

Assessment of Stream Restoration Structures in Streams of North-Central Pennsylvania

Interest in stream restoration has increased over the last two decades, leading to a growth in the industry to the point that it has become a 1 billion dollar per year enterprise (Bernhart et al 2005, Thompson 2002). In north-central Pennsylvania alone, over $9 million has been spent since 1999 on stream restoration projects, from the designing stage to actual construction and reconstruction of the sites. Even though a extensive amount of money is being spent on the construction of these projects, very little to no post-monitoring is taking place. Without post-monitoring of the projects, it is unknown if they actually work. After a successful statewide stream restoration assessment was completed in North Carolina by the advisor of this project, it was discussed to undertake a similar one for the state of Pennsylvania starting with the north-central region. This includes Bradford, Cambria, Cameron, Centre, Columbia, Lycoming, McKean, Montour, Northumberland, Potter, Sullivan, Tioga, and Union Counties. Within these 13 counties over 60 restoration projects have been implemented since the 1990s ranging in type from FGM structures to Fish and Boat Commission habitat structures. Twenty-two of the restoration sites comprising of 58,255 feet of restoration work were selected for individual site assessment during March 2008-May 2009. Over 300 structures were assessed during this period of time for structural integrity and the degree to which the adjacent bed and banks had been affected by unintended erosion or deposition. Approximately 75% of the structures have sustained some structural damage (ranking \u3e1) or erosion or deposition (ranking \u3e1). Thirty-five percent of the structures have sustained significant damage (ranking \u3e2) or significant erosion or deposition (ranking \u3e3). Most of the damage (63% of all structures) is related to erosion or deposition which can impact the functionality of the structure. Many of the streams in north-central Pennsylvania are experiencing pulses of aggradation of gravel-cobble size clasts throughout the stream system. This pulse of gravel is contributing to the partial burial of individual structures and may fill in the pool that was created by the structure. Out of the four highly used structure types (cross vanes, j-hooks, log vanes, and rock vanes), j-hooks and rock vanes sustained the highest percentage of damage compared to the other two structures. Much more work needs to be completed in this region before we can fully grasp an understanding for failure of the various structures

Geomorphology of icy debris fans: Delivery of ice and sediment to valley glaciers decoupled from icecaps

The pace and volume of mass flow processes contributing ice and sediment to icy debris fans (IDFs) were documented at sites in Alaska and New Zealand by integrating field observations, drone and time-lapse imagery, ground penetrating radar, and terrestrial laser scanning. Largely unstudied, IDFs are supraglacial landforms at the mouths of bedrock catchments between valley glaciers and icecaps. Time-lapse imagery recorded 300–2300 events reaching 15 fans during intervals from nine months to two years. Field observations noted hundreds of deposits trapped within catchments weekly that were later remobilized onto fans. Deposits were mapped on images taken three to four times per day. Most events were ice avalanches (58%–100%). Slush avalanches and/or flows were common in spring and fall (0%–65%). Icy debris flows were \u3c5% of the events, observed only at sites with geomorphically complex catchments. Rockfalls were common within catchments; few directly reached a fan. Site selection provided a spectrum of catchment relationships between icecaps and fans. The largest most active fans occur below hanging glaciers or short chutes between the icecap and glacier and were dominated by ice avalanches, slush avalanches, and slush flows. Larger, complex catchments allowed temporary storage of ice and sediment that were later remobilized into ice and slush avalanches and debris flows. Unlike alluvial settings where larger fans are associated with larger catchments, there are variable relationships between IDF area and catchment area. Exceptionally active and dynamic compared to alluvial fans, the studied IDFs exhibited annual resurfacing rates of 300%–\u3e4000%. Annual contributions by mass flows ranged from 133,200 to 5,200,000 m3, representing 3%–56% of fan volume. Although ablation occurred, mainly during summers, significant ice transfer occurred through fan subsurface areas to adjacent valley glaciers. Icy debris fans annually contributed \u3c1%–~24% of the mass of adjacent valley glaciers. Small glaciers (e.g., McCarthy Glacier, Alaska) showed minor thinning (\u3c1 m/yr) compared to larger glaciers (e.g., La Perouse, Douglas, and Mueller Glaciers, New Zealand) that lost \u3e5–10 m/yr over the hundreds of meters of valley glacier adjacent to the IDFs studied. Some IDFs lengthened in response to thinning of valley glaciers. Icy debris fans supplied significant ice and sediment to valley glaciers, slowing the rate of deglaciation. Results of this study have implications toward managing hazards and predicting glacial mass balance in alpine regions. For example, having quantitative information about the role of ice contribution from IDFs to valley glaciers may result in forecasting a lower rate of deglaciation than traditionally recognized for some glaciers decoupled from icecaps

Assessing Ground Penetrating Radar\u27s Ability to Image Subsurface Characteristics of Icy Debris Fans in Alaska and New Zealand

Icy debris fans have recently been described as fan shaped depositional landforms associated with (or formed during) deglaciation, however, the subsurface characteristics remain essentially undocumented. We used ground penetrating radar (GPR) to non-invasively investigate the subsurface characteristics of icy debris fans (IDFs) at McCarthy Glacier, Alaska, USA and at La Perouse Glacier, South Island of New Zealand. IDFs are largely unexplored paraglacial landforms in deglaciating alpine regions at the mouths of bedrock catchments between valley glaciers and icecaps. IDFs receive deposits of mainly ice and minor lithic material through different mass-flow processes, chiefly ice avalanche and to a lesser extent debris flow, slushflow, and rockfall. We report here on the GPR signal velocity observed from 15 different wide-angle reflection/refraction (WARR) soundings on the IDFs and on the McCarthy Glacier; the effect of GPR antenna orientation relative to subsurface reflections; the effect of spreading direction of the WARR soundings relative to topographic contour; observed differences between transverse electric (TE) and transverse magnetic (TM) antenna polarization; and a GPR profile extending from the McCarthy Glacier onto an IDF. Evaluation of the WARR soundings indicates that the IDF deposits have a GPR signal velocity that is similar to the underlying glacier, and that the antenna polarization and orientation did not prevent identification of GPR reflections. The GPR profile on the McCarthy Glacier indicates that the shallowest material is layered, decreases in thickness down fan, and has evidence of brittle failure planes (crevasses). The GPR profile and WARR soundings collected in 2013 indicate that the thickness of the McCarthy Glacier is 82 m in the approximate middle of the cirque and that the IDF deposits transition with depth into flowing glacial ice

Assessing Ground Penetrating Radar’s Ability to Image Subsurface Characteristics of Icy Debris Fans in Alaska and New Zealand

Icy debris fans have recently been described as fan shaped depositional landforms associated with (or formed during) deglaciation, however, the subsurface characteristics remain essentially undocumented. We used ground penetrating radar (GPR) to non-invasively investigate the subsurface characteristics of icy debris fans (IDFs) at McCarthy Glacier, Alaska, USA and at La Perouse Glacier, South Island of New Zealand. IDFs are largely unexplored paraglacial landforms in deglaciating alpine regions at the mouths of bedrock catchments between valley glaciers and icecaps. IDFs receive deposits of mainly ice and minor lithic material through different mass-flow processes, chiefly ice avalanche and to a lesser extent debris flow, slushflow, and rockfall. We report here on the GPR signal velocity observed from 15 different wide-angle reflection/refraction (WARR) soundings on the IDFs and on the McCarthy Glacier; the effect of GPR antenna orientation relative to subsurface reflections; the effect of spreading direction of the WARR soundings relative to topographic contour; observed differences between transverse electric (TE) and transverse magnetic (TM) antenna polarization; and a GPR profile extending from the McCarthy Glacier onto an IDF. Evaluation of the WARR soundings indicates that the IDF deposits have a GPR signal velocity that is similar to the underlying glacier, and that the antenna polarization and orientation did not prevent identification of GPR reflections. The GPR profile on the McCarthy Glacier indicates that the shallowest material is layered, decreases in thickness down fan, and has evidence of brittle failure planes (crevasses). The GPR profile and WARR soundings collected in 2013 indicate that the thickness of the McCarthy Glacier is 82 m in the approximate middle of the cirque and that the IDF deposits transition with depth into flowing glacial ice

Geomorphic Problems with Natural Design Methods Applied to Stream Channel Restoration: Examples from a Comprehensive Survey of Projects in North Carolina and Implications for the Susquehanna Watershed

Federal, state, local, and private funds are increasingly being committed to stream restoration projects in the United States, to stabilize stream channels, reduce bank erosion, and improve aquatic habitat. The majority of these projects utilize a method known as Natural Channel Design, which relies on the classification of channels into Rosgen type stream reaches and assigns a prescriptive restorative treatment. Hallmarks of this strategy employ in-channel rock structures such as cross-vanes, J-hooks, and rock weirs as well as bank treatments such as rootwads, revetments, and live stakings. Little information exists about the performance of these projects. We are finishing a comprehensive 3-year survey of 400 restoration projects for the state of North Carolina completed within the past 8 years. The evaluation of these widely-used techniques can provide insights into the physical performance of restoration designs. The data are intended to provide guidelines for the design of restoration projects, and can be applied to similar projects in the Susquehanna watershed. Field surveys show that at about a third of examined sites, more than 70% of in-stream structures have sustained significant damage so that structures no longer perform their intended function; numerous others exhibit less severe damage. Some structures were rendered non-functional after the first overbank flood. In some cases, structures were installed, damaged, and repaired, only to be damaged again. Damages vary, but a common problem was the erosion around the landward side of J-hooks and cross-vanes during overbank flows, accelerating bank erosion locally and stranding the rock structures as ineffective midchannel islands. Approximately 30 % of the damaged structures were affected by either burial or bar development, which led to channel migration and flanking of the structure along newly eroded banks. Channels with high failure rates are associated with easily erodible bed and bank materials (in comparison to stream power) and/or streams with high rates of bedload transport. A preliminary review of design documents shows that analyses of the past or current geomorphic conditions were rarely undertaken, and analyses of sediment transport continuity through the restored reach were virtually non-existent. In-stream structures are designed to handle bankfull or lower flows. During overbank flows (which occur on-theaverage every 1-2 years), the structures become mere roughness elements. In some cases they may even accelerate bank erosion and channel migration. Moreover, many projects fail to consider changes in sediment and water yield that have occurred, or are occurring, due to historical land use changes and/or major flood events in upstream portions of the drainage basins. In these cases, streams may be in a protracted phase of morphologic adjustment, rendering restorative structures virtually useless A similar evaluation of restoration projects is needed in the Susquehanna watershed. The large number of sites in North Carolina exhibiting damaged structures within a few years of construction strongly suggests that more rigorous geomorphic and hydrological analyses are required to improve the performance of restoration projects. Even though this will initially require more time, money, and trained personnel, improvements in the success of stream restoration projects are possible by integrating geomorphic knowledge of river channel behavior with the planning and designing of restoration projects