Geology topics

Andrew J. Miller

Publications and source records attributed to Andrew J. Miller.

6 recordsLinked to original sources

USGS2024

Remotely mapping gullying and incision in Maryland Piedmont headwater streams using repeat airborne lidar

Headwater streams can contribute significant amounts of fine sediment to downstream waterways, especially when severely eroded and incised. Potential upstream sediment source identification is crucial for effective management of water quality, aquatic habitat, and sediment loads in a watershed. This study explored topographic openness (TO) derived from 1-m lidar for its ability to predict incision in headwater streams and to remotely detect changes in incision over time. Field surveys were conducted in one forested and two recently urbanized headwater watersheds in the Maryland Piedmont physiographic province, USA to characterize the level of stream channel incision (none, moderate, or severe) in the main stem of each watershed. Predictions of the severity of stream channel incision derived from TO were compared against the field surveys. Channel incision was detected with an overall accuracy of 67 %, with best performance in reaches with either severe or no incision (79–86 % accuracy). The method was also applied to repeat lidar collected over the same area to model the extent of channel incision in 2002 before urban development began and in 2008 and 2013 during active construction in the urban watersheds. Results showed increasing incision over time in all three watersheds, with similar patterns in the forested and urban watersheds. This new method of remotely measuring channel incision can be used to identify potential sediment sources across a watershed, enhance water and habitat quality predictions, and detect changes over time where multiple years of overlapping lidar are available.

Maryland↗

USGS2022

Ephemeral stream network extraction from lidar-derived elevation and topographic attributes in urban and forested landscapes

Under-representations of headwater channels in digital stream networks can result in uncertainty in the magnitude of headwater habitat loss, stream burial, and watershed function. Increased availability of high-resolution (<2 m) elevation data makes the delineation of headwater channels more attainable. In this study, elevation data derived from light detection and ranging was used to predict ephemeral stream networks across a forested and urban watershed in the Maryland Piedmont USA. A method was developed using topographic openness (TO) and wetness index to remotely predict the extent of stream networks. Predicted networks were compared against a comprehensive field survey of the ephemeral network in each watershed to evaluate performance. Comparisons were also made to the U.S. Geological Survey National Hydrography Dataset (NHD) and a flow accumulation approach where a single drainage area threshold defined channel initiation. Although the NHD and flow accumulation methods resulted in low commission errors, omission errors were highest in these networks. The TO-based networks detected a larger number of ephemeral channels, but with higher commission error. Small ephemeral channels with less defined banks or originating at groundwater seeps were difficult to detect in all methods. Comparisons between forested and urban watersheds also highlight the difficulty of identifying headwater channels using topographic attributes in human-modified landscapes.

Maryland↗

USGS2019

River‐valley morphology, basin size, and flow‐event magnitude interact to produce wide variation in flooding dynamics

Inundation dynamics are a key driver of ecosystem form and function in river‐valley bottoms. Inundation itself is an outcome of multi‐scalar interactions and can vary strongly within and among river reaches. As a result, establishing to what degree and how inundation dynamics vary spatially both within and among river reaches can be challenging. The objective of this study was to understand how river‐valley morphology, basin size, and flow‐event magnitude interact to affect inundation dynamics in river‐valley bottoms. We used 2D hydraulic models to simulate inundation in four river reaches from Maryland's Piedmont physiographic province, and qualitatively and quantitatively summarized within‐ and among‐reach patterns of inundation extent, duration, depth, shear stress, and wetting frequencies. On average, reaches from confined valley settings experienced less extensive flooding, shorter durations and shallower depths, stronger gradients of maximum shear stress, and relatively infrequent wetting compared to reaches from unconfined settings. These patterns were generally consistent across flow‐event magnitudes. Patterns of within‐reach flooding across event magnitudes revealed complex interactions between hydrology and surface topography. We concluded that valley morphology had a greater impact on flooding patterns than basin size: Inundation patterns were more consistent across reaches of similar morphology than similar basin size, but absolute values of inundation characteristics varied between large and small basins. Our results showed that the manifestation of out‐of‐bank flows in valley floors can vary widely depending on geomorphic context, even within a single physiographic province, which suggests that hydrologic and hydraulic conditions experienced on the valley floor may not be well represented by existing hydrologic metrics derived from discharge data alone. We thus support the notion that 2D hydraulic models can be useful hydrometric tools for cross‐scale investigations of floodplain ecosystems.

Maryland↗

USGS2014

Tracking geomorphic signatures of watershed suburbanization with multi-temporal LiDAR

Urban development practices redistribute surface materials through filling, grading, and terracing, causing drastic changes to the geomorphic organization of the landscape. Many studies document the hydrologic, biologic, or geomorphic consequences of urbanization using space-for-time comparisons of disparate urban and rural landscapes. However, no previous studies have documented geomorphic changes from development using multiple dates of high-resolution topographic data at the watershed scale. This study utilized a time series of five sequential light detection and ranging (LiDAR) derived digital elevation models (DEMs) to track watershed geomorphic changes within two watersheds throughout development (2002–2008) and across multiple spatial scales (0.01–1 km 2 ). Development-induced changes were compared against an undeveloped forested watershed during the same time period. Changes in elevations, slopes, hypsometry, and surface flow pathways were tracked throughout the development process to assess watershed geomorphic alterations. Results suggest that development produced an increase in sharp topographic breaks between relatively flat surfaces and steep slopes, replacing smoothly varying hillslopes and leading to greater variation in slopes. Examinations of flowpath distributions highlight systematic modifications that favor rapid convergence in unchanneled upland areas. Evidence of channel additions in the form of engineered surface conduits is apparent in comparisons of pre- and post-development stream maps. These results suggest that topographic modification, in addition to impervious surfaces, contributes to altered hydrologic dynamics observed in urban systems. This work highlights important considerations for the use of repeat LiDAR flights in analyzing watershed change through time. Novel methods introduced here may allow improved understanding and targeted mitigation of the processes driving geomorphic changes during development and help guide future research directions for development-based watershed studies.

Geomorphology↗

USGS1993

Flood hydrology and geomorphic effects on river channels and flood plains: The flood of November 4-5, 1985, in the South Branch Potomac River Basin of West Virginia

The November 1985 flood was the largest recorded in the South Branch Potomac River basin. Discharges exceeded values estimated for a recurrence interval of 500 yr at four of six stations in the basin. Flow velocities in the channel were as high as 4.6 m/s and may have exceeded 6 m/s at some locations; estimated values of unit stream power at U.S. Geological Survey gage locations were as high as 988 W/m2 and may have exceeded 2,500 W/m 2 at some locations. Along the three forks of the South Branch Potomac River, discharges of 1,000-7,000 m 3 /s flowed through valley cross sections that ranged in width from less than 70 m to 1,700 m, and, as a result, hydraulic conditions were extremely variable. Valley constrictions and expansions were important determinants of erosion and deposition patterns. Geomorphic impacts on valley floors along the three forks of the South Branch Potomac River included formation of a wide array of erosion and deposition features. Flood-generated erosion features included longitudinal grooves, scour marks, widened channels, stripped flood plains, chutes, anastomosing erosion channels, and jetshaped erosion forms. Deposition features were generally adjacent to eroded areas and included channel gravel bars, gravel splays, gravel and sand sheets, isolated gravel bars and sand dunes on flood plains, wake deposits, and backwater deposits. Mapping of erosion damage classes along 384 km of channel and valley floor revealed that 82.8 percent of the valley length experienced at least incipient erosion, 30.2 percent experienced severe erosion, and 5.7 percent experienced catastrophic erosion of the valley floor. Reach-average values of unit stream power were positively correlated with the percent of the valley reach that experienced severe erosion; percentages of 50 percent or more were associated with average values of 200-500 W/m 2 . These results suggest that, with further research, it should be possible to define threshold conditions for bottomland erosion.

West Virginia↗

USGS1987

Shore erosion as a sediment source to the tidal Potomac River, Maryland and Virginia

The shoreline of the tidal Potomac River attained its present form as a result of the Holocene episode of sea-level rise; the drowned margins of the system are modified by wave activity in the shore zone and by slope processes on banks steepened by basal-wave erosion. Shore erosion leaves residual sand and gravel in shallow water and transports silt and clay offshore to form a measurable component of the suspended-sediment load of the tidal Potomac River. Erosion rates were measured by comparing digitized historical shoreline maps and modern maps, and by comparing stereopairs of aerial photographs taken at different points in time, with the aid of an interactive computer-graphics system and a digitizing stereoplotter. Cartographic comparisons encompassed 90 percent of the study reach and spanned periods of 38 to 109 years, with most measurements spanning at least 84 years. Photogrammetric comparisons encompassed 49 percent of the study reach and spanned 16 to 40 years. Field monitoring of erosion rates and processes at two sites, Swan Point Neck, Maryland, and Mason Neck, Virginia, spanned periods of 10 to 18 months. Estimated average recession rates of shoreline in the estuary, based on cartographic and photogrammetric measurements, were 0.42 to 0.52 meter per annum (Virginia shore) and 0.31 to 0.41 meter per annum (Maryland shore). Average recession rates of shoreline in the tidal river and transition zone were close to 0.15 meter per annum. Estimated average volume-erosion rates along the estuary were 1.20 to 1.87 cubic meters per meter of shoreline per annum (Virginia shore) and 0.56 to 0.73 cubic meter per meter of shoreline per annum (Maryland shore); estimated average volume-erosion rates along the shores of the tidal river and transition zone were 0.55 to 0.74 cubic meter per meter of shoreline per annum. Estimated total sediment contributed to the tidal Potomac River by shore erosion was 0.375 x 10 6 to 0.565 x 10 6 metric tons per annum; of this, the estimated amount of silt and clay ranged from 0.153x10 6 to 0.226x10 6 metric tons per annum. Between 49 and 60 percent of the sediment was derived from the Virginia shore of the estuary; 14 to 18 percent was derived from the Maryland shore of the estuary; and 23 to 36 percent was derived from the shores of the tidal river and transition zone. The adjusted modern estimate of sediment eroded from the shoreline of the estuary is about 55 percent of the historical estimate. Sediment eroded from the shoreline accounted for about 6 to 9 percent of the estimated total suspended load for the tidal Potomac River during water years 1979 through 1981 and for about 11 to 18 percent of the suspended load delivered to the estuary during the same period. Annual suspended-sediment loads derived from upland source areas fluctuated by about an order of magnitude during the 3 years of record (1979-81); shore erosion may have been a more important component of the sediment budget during periods of low flow than during periods of higher discharges. Prior to massive land clearance during the historical period of intensive agriculture in the 18th and 19th centuries, annual sediment loads from upland sources probably were smaller than they are at present; under these circumstances shore erosion would have been an important component of the sediment budget. At current rates of sediment supply, relative sea-level rise, and shoreline recession, the landward parts of the tidal Potomac River are rapidly being filled by sediment. If these rates were to remain constant over time, and no sediment were to escape into Chesapeake Bay, the tidal river and transition zone would be filled within 600 years, and the total system would be filled in less than 4,000 years. Given a slower rate of sediment supply, comparable to the measured rate during the low-flow 1981 water year, the volume of the tidal Potomac River might remain relatively stable or even increase over time. Changes in rates

Water Supply Paper↗