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At least 19 recordsLinked to original sources
USGS2013

Characterizing response of total suspended solids and total phosphorus loading to weather and watershed characteristics for rainfall and snowmelt events in agricultural watersheds

Understanding the response of total suspended solids (TSS) and total phosphorus (TP) to influential weather and watershed variables is critical in the development of sediment and nutrient reduction plans. In this study, rainfall and snowmelt event loadings of TSS and TP were analyzed for eight agricultural watersheds in Wisconsin, with areas ranging from 14 to 110 km2 and having four to twelve years of data available. The data showed that a small number of rainfall and snowmelt runoff events accounted for the majority of total event loading. The largest 10% of the loading events for each watershed accounted for 73–97% of the total TSS load and 64–88% of the total TP load. More than half of the total annual TSS load was transported during a single event for each watershed at least one of the monitored years. Rainfall and snowmelt events were both influential contributors of TSS and TP loading. TSS loading contributions were greater from rainfall events at five watersheds, from snowmelt events at two watersheds, and nearly equal at one watershed. The TP loading contributions were greater from rainfall events at three watersheds, from snowmelt events at two watersheds and nearly equal at three watersheds. Stepwise multivariate regression models for TSS and TP event loadings were developed separately for rainfall and snowmelt runoff events for each individual watershed and for all watersheds combined by using a suite of precipitation, melt, temperature, seasonality, and watershed characteristics as predictors. All individual models and the combined model for rainfall events resulted in two common predictors as most influential for TSS and TP. These included rainfall depth and the antecedent baseflow. Using these two predictors alone resulted in an R 2 greater than 0.7 in all but three individual models and 0.61 or greater for all individual models. The combined model yielded an R 2 of 0.66 for TSS and 0.59 for TP. Neither the individual nor the combined models were substantially improved by using additional predictors. Snowmelt event models were statistically significant for individual and combined watershed models, but the model fits were not all as good as those for rainfall events (R 2 between 0.19 and 0.87). Predictor selection varied from watershed to watershed, and the common variables that were selected were not always selected in the same order. Influential variables were commonly direct measures of moisture in the watershed such as snowmelt, rainfall + snowmelt, and antecedent baseflow, or measures of potential snowmelt volume in the watershed such as air temperature.

Wisconsin↗
USGS2022

Fires, floods and other extreme events – How watershed processes under climate change will shape our coastlines

Ongoing sea-level rise has brought renewed focus on terrestrial sediment supply to the coast because of its strong influence on whether and how long beaches, marshes and other coastal landforms may persist into the future. Here, we summarise findings of sediment discharge from several coastal rivers, revealing that infrequent, large-magnitude events have disproportionate influence on the morphodynamics of coastal landforms and littoral cells. These event-dominated effects are most pronounced for small, steep mountainous rivers that supply beach and wetland sediment along the world’s active tectonic margins, although infrequent events are important drivers of sediment discharge for rivers worldwide. Additionally, extreme events (recurrence intervals of decades to centuries) that follow wildfires, earthquakes, volcanic eruptions, extreme precipitation or – most notably – combinations of these factors can redefine coastal sediment budgets and morphology. Some of these extreme events (e.g., wildfires plus rainfall) are increasing in magnitude and frequency under modern climate warming, with the likely result of increasing sediment flux to affected coastlines. Climate change is also altering watershed processes in both high latitudes and high altitudes, resulting in increased sediment supply to downstream catchments. We conclude that sediment inputs to coastal systems are highly variable with time, and that the variability and trends in sediment input are as important to characterise as long-term averages.

Cambridge Prisms: Coastal Futures↗
USGS2024

The 17 January 1994 Northridge, California, earthquake: A retrospective analysis

The 17 January 1994 Northridge, California, earthquake was a watershed event, with far-reaching societal and scientific impacts. The earthquake, which occurred in the early days of both broadband seismic networks and the Internet, spurred advances in seismic monitoring, real-time systems, and development of data products. Motivated by the 30th anniversary of the earthquake, we present a brief retrospective of the earthquake and its impact, and reconsider both ground motions and the aftershock distribution using modern tools and best-available data. With improvements in instrumentation and analysis methodology, recent earthquakes continue to reveal increasing complexity of ground motions, fault systems, and earthquake ruptures. Even in the absence of data from state-of-the art instrumentation, a retrospective consideration of ground motion data from the Northridge earthquake reveals complexities beyond what could be characterized (and modeled) thirty years ago. Aftershock relocations for both the 1971 Sylmar and 1994 Northridge earthquakes also reveal an updated view of fault complexity. Our study does provide a cautionary tale regarding legacy data sets and research results that are not easily accessible, which can result in discrepancies between catalog data and products from best-available science. We also briefly describe outreach products produced as part of the anniversary commemoration.

California↗
USGS2019

Hysteretic response of solutes and turbidity at the event scale across forested tropical montane watersheds

Concentration-discharge relationships are a key tool for understanding the sourcing and transport of material from watersheds to fluvial networks. Storm events in particular provide insight into variability in the sources of solutes and sediment within watersheds, and the hydrologic pathways that connect hillslope to stream channel. Here we examine high-frequency sensor-based specific conductance and turbidity data from multiple storm events across two watersheds (Quebrada Sonadora and Rio Icacos) with different lithology in the Luquillo Mountains of Puerto Rico, a forested tropical ecosystem. Our analyses include Hurricane Maria, a category 5 hurricane. To analyze hysteresis, we used a recently developed set of metrics to describe and quantify storm events including the hysteresis index (HI), which describes the directionality of hysteresis loops, and the flushing index (FI), which can be used to infer whether the mobilization of material is source or transport limited. We also examine the role of antecedent discharge to predict hysteretic behavior during storms. Overall, specific conductance and turbidity showed contrasting responses to storms. The hysteretic behavior of specific conductance was very similar across sites, displaying clockwise hysteresis and a negative flushing index indicating proximal sources of solutes and consistent source limitation. In contrast, the directionality of turbidity hysteresis was significantly different between watersheds, although both had strong flushing behavior indicative of transport limitation. Overall, models that included antecedent discharge did not perform any better than models with peak discharge alone, suggesting that the magnitude and trajectory of an individual event was the strongest driver of material flux and hysteretic behavior. Hurricane Maria produced unique hysteresis metrics within both watersheds, indicating a distinctive response to this major hydrological event. The similarity in response of specific conductance to storms suggests that solute sources and pathways are similar in the two watersheds. The divergence in behavior for turbidity suggests that sources and pathways of particulate matter vary between the two watersheds. The use of high-frequency sensor data allows the quantification of storm events while index-based metrics of hysteresis allow for the direct comparison of complex storm events across a heterogeneous landscape and variable flow conditions.

Luquillo Mountains↗
USGS2022

Stormwater quantity and quality in selected urban watersheds in Hampton Roads, Virginia, 2016–2020

Urbanization can substantially alter sediment and nutrient loadings to streams. Although a growing body of literature has documented these processes, conditions may vary widely by region and physiographic province (PP). Substantial investments are made by localities to meet federal, state, and local water-quality goals and locally relevant monitoring data are needed to appropriately set standards and track progress. In 2016, a long-term stormwater monitoring program was initiated to characterize water-quality and streamflow conditions and compute average annual nutrient- and sediment-loading rates across the three dominant land-use types—commercial (COM), high-density residential, and single-family residential (SFR)—in the Hampton Roads metropolitan region within the Coastal Plain PP in southeastern Virginia. This report summarizes the first five years of data collection to (1) assess patterns in streamflow and water chemistry across the three major land-use types in the region; (2) compute annual sediment and nutrient loads; and (3) compare annual loading rates to those in other urbanized regions. Patterns in watershed hydrology characteristics and conditions were similar to those observed in other urban monitoring studies. Base-flow indices were lower and stream flashiness indices were higher in the study watersheds compared to those in less developed reference watersheds. These patterns reflect a decrease in infiltration and consequent increase in storm runoff as a result of urbanization. Stream flashiness was strongly positively related to degree of impervious land cover and negatively to watershed area. Hydrologic metrics varied across the land-use gradient, reflecting greater and more rapid runoff in the COM watersheds than in SFR watersheds. Event-based analyses conducted exclusively on periods of runoff highlight longer duration events, longer time-to-peak streamflow, and a longer lag between peak precipitation and peak streamflow in SFR watersheds, and higher stormflow yields, runoff ratios, and peak flows in COM watersheds. Event-based metrics varied seasonally because of regional meteorological patterns. Concentrations of total suspended solids (TSS) and total phosphorus (TP) were positively correlated to streamflow, whereas concentrations of total nitrogen (TN) varied little across the hydrologic regime. Phosphorus composition varied spatially and seasonally—the proportion of orthophosphate (PO 4 3- ) was highest in samples collected from stations draining residential land-use types and was elevated in summer and fall. Nitrogen composition varied with hydrologic condition: nitrate plus nitrite (NO 3 - ) dominance during base flow shifted to total organic nitrogen (TON) dominance during periods of runoff. For all three major constituents (TSS, TP, and TN), concentrations were highest in SFR watersheds, whereas yields were greatest in COM watersheds. This seeming contradiction in concentration and yield across land-use types occurred because of spatial differences in streamflow yield. The network average TSS yield in Hampton Roads was lower than that in comparable networks in Fairfax County, Virginia, and Gwinnett County, Georgia, a difference that may reflect dissimilarities in the topographic and soil characteristics of the Coastal Plain versus those in Piedmont PPs, as well as differences in engineered concrete stormwater conveyances versus earthen streams. The average annual TP yield in Hampton Roads was higher than averages reported in comparison studies and was primarily driven by elevated PO 4 3- . Elevated PO 4 3- yields may be related to unique soil and geological features of the Coastal Plain PP that limit phosphorus retention. Total nitrogen yields in the Hampton Roads and Fairfax County networks were similar; however, composition did vary, with greater total organic nitrogen yields in Hampton Roads and greater NO 3 - yields in Fairfax County. Cross-correlation analyses and mass-volume curves were used to assess the timing of sediment and nutrient loadings. The majority of TSS and TP was typically transported during the initial phase of a storm-runoff event, a phenomenon commonly termed the “first flush.” Although TN concentrations typically peaked within an hour of peak streamflow, reflecting the particulate dominance of TN during stormflows, and loadings were greater during the early phase of most storm events, the stricter first-flush criterion was rarely met. This suggests that the most abundant sources of TN in these watersheds are not as directly connected to the stormwater-conveyance system as are TSS and TP.

Virginia↗
USGS2006

Solute sources in stream water during consecutive fall storms in a northern hardwood forest watershed: A combined hydrological, chemical and isotopic approach

Understanding the effects of climate change including precipitation patterns has important implications for evaluating the biogeochemical responses of watersheds. We focused on four storms in late summer and early fall that occurred after an exceptionally dry period in 2002. We analyzed not only the influence of these storms on episodic chemistry and the role of different water sources in affecting surface water chemistry, but also the relative contributions of these storms to annual biogeochemical mass balances. The study site was a well studied 135-ha watershed in the Adirondack Park of New York State (USA). Our analyses integrated measurements on hydrology, solute chemistry and the isotopic composition of NO 3 − (δ 15 N and δ 18 O) and SO 4 2− (δ 34 S and δ 18 O) to evaluate how these storms affected surface water chemistry. Precipitation amounts varied among the storms (Storm 1: Sept. 14–18, 18.5 mm; Storm 2: Sept. 21–24, 33 mm; Storm 3: Sept. 27–29, 42.9 mm; Storm 4: Oct. 16–21, 67.6 mm). Among the four storms, there was an increase in water yields from 2 to 14%. These water yields were much less than in studies of storms in previous years at this same watershed when antecedent moisture conditions were higher. In the current study, early storms resulted in relatively small changes in water chemistry. With progressive storms the changes in water chemistry became more marked with particularly major changes in C b (sum of base cations), Si, NO 3 − , and SO 4 2− , DOC and pH. Analyses of the relationships between Si, DOC, discharge and water table height clearly indicated that there was a decrease in ground water contributions (i.e., lower Si concentrations and higher DOC concentrations) as the watershed wetness increased with storm succession. The marked changes in chemistry were also reflected in changes in the isotopic composition of SO 4 2− and NO 3 − . There was a strong inverse relationship between SO 4 2− concentrations and δ 34 S values suggesting the importance of S biogeochemical redox processes in contributing to SO 4 2− export. The isotopic composition of NO 3 − in stream water indicated that this N had been microbially processed. Linkages between SO 4 2− and DOC concentrations suggest that wetlands were major sources of these solutes to drainage waters while the chemical and isotopic response of NO 3 − suggested that upland sources were more important. Although these late summer and fall storms did not play a major role in the overall annual mass balances of solutes for this watershed, these events had distinctive chemistry including depressed pH and therefore have important consequences to watershed processes such as episodic acidification, and the linkage of these processes to climate change.

Biogeochemistry↗
USGS2017

Dissolved organic matter compositional change and biolability during two storm runoff events in a small sgricultural watershed

Agricultural watersheds are globally pervasive, supporting fundamentally different organic matter source, composition, and concentration profiles in comparison to natural systems. Similar to natural systems, agricultural storm runoff exports large amounts of organic carbon from agricultural land into waterways. But intense management of upper soil layers, waterway channelization, wetland and riparian habitat removal, and postharvest vegetation removal promise to uniquely drive organic matter release to waterways. During a winter first flush and a subsequent storm event, this study investigated the influence of a small agricultural watershed on dissolved organic matter (DOM) source, composition, and biolability. Storm water discharge released strongly terrestrial yet biolabile (23 to 32%) dissolved organic carbon (DOC). Following a 21 day bioassay, a parallel factor analysis identified an 80% reduction in a protein-like (phenylpropyl) component (C2) that was previously correlated to lignin phenol concentration, and a 10% reduction in a humic-like, terrestrially sourced component (C4). Storm-driven releases tripled DOC concentration (from 2.8 to 8.7 mg L −1 ) during the first flush event in comparison to base flow and were terrestrially sourced, with an eightfold increase in vascular plant derived lignin phenols (23.0 to 185 μg L −1 ). As inferred from system hydrology, lignin composition, and nitrate as a groundwater tracer, an initial pulse of dilute water from the upstream watershed caused a counterclockwise DOC hysteresis loop. DOC concentrations peaked after 3.5 days, with the delay between peak discharge and peak DOC attributed to storm water hydrology and a period of initial water repellency of agricultural soils, which delayed DOM leaching.

California↗
USGS2001

Evaluation of the Effects of Development on Peak-Flow Hydrographs for Collyer Brook, Maine

The development of former agricultural or forested lands creates more impervious areas and drainage improvements that can increase the volume of runoff and decrease infiltration and ground-water recharge in a watershed. Drainage improvements also can improve the conveyance of runoff, decreasing the time of rise to peak flow between the start of a rainfall event and the peak surface-water runoff, and likewise decreasing the duration of the peak-flow event. The watershed of Collyer Brook in southern Maine was studied to evaluate the effect of land-use changes on peakflow hydrographs because of the known development in the area during the past 35 years and the availability of aerial photos and streamflow data for this time period. Although aerial photography indicates that suburban development has increased in the watershed between 1964 and 1999, the overall effect of suburbanization on rainfall-runoff processes in the watershed did not produce a statistically detectable change in the peak-flow hydrographs for Collyer Brook.

Water-Resources Investigations Report↗
USGS2000

Concentrations and characteristics of organic carbon in surface water in Arizona: Influence of urbanization

Dissolved (DOC) and total (TOC) organic carbon concentrations and compositions were studied for several river systems in Arizona, USA. DOC composition was characterized by ultraviolet and visible absorption and fluorescence emission (excitation wavelength of 370 nm) spectra characteristics. Ephemeral sites had the highest DOC concentrations, and unregulated perennial sites had lower concentrations than unregulated intermittent sites, regulated sites, and sites downstream from wastewater-treatment plants (p < 0.05). Reservoir outflows and wastewater-treatment plant effluent were higher in DOC concentration (p < 0.05) and exhibited less variability in concentration than inflows to the reservoirs. Specific ultraviolet absorbance values at 254 nm were typically less than 2 m-1(milligram DOC per liter)-1 and lower than values found in most temperate-region rivers, but specific ultraviolet absorbance values increased during runoff events. Fluorescence measurements indicated that DOC in desert streams typically exhibit characteristics of autochthonous sources; however, DOC in unregulated upland rivers and desert streams experienced sudden shifts from autochthonous to allochthonous sources during runoff events. The urban water system (reservoir systems and wastewater-treatment plants) was found to affect temporal variability in DOC concentration and composition. (C) 2000 Elsevier Science B.V.Dissolved (DOC) and total (TOC) organic carbon concentrations and compositions were studied for several river systems in Arizona, USA. DOC composition was characterized by ultraviolet and visible absorption and fluorescence emission (excitation wavelength of 370 nm) spectra characteristics. Ephemeral sites had the highest DOC concentrations, and unregulated perennial sites had lower concentrations than unregulated intermittent sites, regulated sites, and sites downstream from wastewater-treatment plants (p<0.05). Reservoir outflows and wastewater-treatment plant effluent were higher in DOC concentration (p<0.05) and exhibited less variability in concentration than inflows to the reservoirs. Specific ultraviolet absorbance values at 254 nm were typically less than 2 m-1(milligram DOC per liter)-1 and lower than values found in most temperate-region rivers, but specific ultraviolet absorbance values increased during runoff events. Fluorescence measurements indicated that DOC in desert streams typically exhibit characteristics of autochthonous sources; however, DOC in unregulated upland rivers and desert streams experienced sudden shifts from autochthonous to allochthonous sources during runoff events. The urban water system (reservoir systems and wastewater-treatment plants) was found to affect temporal variability in DOC concentration and composition.The influence of urbanization, becoming increasingly common in arid regions, on dissolved organic carbon (DOC) concentrations in surface water resources was studied. DOC concentration and composition, seasonal watershed runoff events, streamflow variations, water management practices, and urban infrastructure in several Arizona watersheds were monitored. Ephemeral sites had the highest DOC levels, and unregulated perennial sites and lower concentrations than unregulated intermittent sites, regulated sites, and sites downstream from wastewater treatment plants. Reservoir outflows and wastewater treatment plant effluent had higher and less variable DOC concentrations than inflows to reservoirs. UV absorbance values, fluorescence measurements, and other indicators suggest that urban water systems (reservoirs and wastewater treatment plants) affect temporal variability in DOC concentration and composition.

Journal of Hydrology↗
USGS2020

Storm impacts on phytoplankton community dynamics in lakes

In many regions across the globe, extreme weather events such as storms have increased in frequency, intensity, and duration due to climate change. Ecological theory predicts that such extreme events should have large impacts on ecosystem structure and function. High winds and precipitation associated with storms can affect lakes via short‐term runoff events from watersheds and physical mixing of the water column. In addition, lakes connected to rivers and streams will also experience flushing due to high flow rates. Although we have a well‐developed understanding of how wind and precipitation events can alter lake physical processes and some aspects of biogeochemical cycling, our mechanistic understanding of the emergent responses of phytoplankton communities is poor. Here we provide a comprehensive synthesis that identifies how storms interact with lake and watershed attributes and their antecedent conditions to generate changes in lake physical and chemical environments. Such changes can restructure phytoplankton communities and their dynamics, as well as result in altered ecological function (e.g., carbon, nutrient and energy cycling) in the short‐ and long‐term. We summarize the current understanding of storm‐induced phytoplankton dynamics, identify knowledge gaps with a systematic review of the literature, and suggest future research directions across a gradient of lake types and environmental conditions.

Global Change Biology↗
USGS2001

It's not just how high; it's how clean: Sampling the spring 2001 flood in the Upper Mississippi River Basin

Floods can cause water-quality problems because of the large amounts of contaminants (sediment, nutrients, pesticides, and bacteria) that can be transported by floodwaters. during the flood on the Upper Mississippi River in 2001, water-quality and water-quality data were collected during near-record streamflow. This is the first time that samples for determining organic wastewater contaminants (pharmaceuticals, hormones, and industrial/household use compounds) and pesticide degradates have been collected during a flood of this magnitude.

Illinois, Iowa, Minnesota, Missouri, Wisconsin↗
USGS2026

Snow simulations predict future changes in rain-on-snow events across the upper Gallatin River watershed, a Greater Yellowstone Ecosystem headwater system

Study region: The upper Gallatin River watershed, an alpine headwater system in the Greater Yellowstone Ecosystem, in Wyoming and Montana. Study focus: As global and regional air temperatures rise, mountain headwaters across the Greater Yellowstone Ecosystem (GYE) are projected to see more precipitation falling as rain. While the hydrologic effects of this snow-to-rain transition depends on a variety of factors, it can lead to an increased occurrence of rain-on-snow (RoS) events. To investigate these changes, we used high-resolution (30 m) SnowModel simulations of the upper Gallatin River watershed. Simulations were run for 2001-2013 using two scenarios: (1) historical meteorology as control and (2) pseudo global warming (PGW) where control air temperature and precipitation conditions were perturbed to represent mean end-of-century conditions under a high-emissions scenario. New hydrological insights for the region: SnowModel outputs show that changes in PGW precipitation and snow accumulation varied with elevation. Warmer air temperatures at low elevations (< 2,500 m) led to less snow accumulation and less precipitation falling as snow. Colder baseline air temperatures for elevations above 2,500 meters (m) resulted in minor reductions in winter snowfall fraction. For PGW simulations, spring (April-June) months were rainier, and elevations above 2,500 m experienced more RoS events. Snowpacks between 2,500-3,100 m generated more snowmelt during RoS events, which was reflected in the watershed average. More high-intensity melt events can affect aquatic habitat, water quality, and the accuracy of streamflow forecasts across the region.

Montana, Wyoming↗
USGS2024

An open-source workflow for scaling burn severity metrics from drone to satellite to support post-fire watershed management

Wildfires are increasing in size and severity across much of the western United States, exposing vulnerable wildland-urban interfaces to post-fire hazards. The Mediterranean chaparral region of Northern California contains many high sloping watersheds prone to hazardous post-fire flood events and identifying watersheds at high risk of soil loss and debris flows is a priority for post-fire response and management. Uncrewed Aerial Systems (UAS; aka drones) offer post-fire management teams the ability to quickly mobilize and survey burned areas with very high-resolution imagery (∼1 cm), facilitating emergency management and post-fire hazard assessment. However, adoption of this technology by hazard response teams may be hindered by complicated workflows for UAS data acquisition, image processing and analysis. We present an open-source workflow using mature Geographic Information Systems (GIS) software and Python packages in a Jupyter Notebook environment that guides users through classification of true-color UAS imagery to generate high resolution burn severity maps which can then be scaled across larger watersheds using Sentinel-2 normalized burn ratio (NBR) images. Soil burn severity classifications using a weighted brightness (WB) image and Char Index (CI) generated from UAS imagery were validated with in-situ data and random stratified points, resulting in the CI having the highest overall accuracy of 87.5%. CI also displayed a marginally stronger relationship over the WB with the post-fire Sentinel-2 NBR, R 2 = 0.79 and R 2 = 0.78 respectively. Our methods offer the unique opportunity to standardize GIS workflows, promoting replication through transparency, while improving the user's understanding of scientific GIS functionality.

California↗
USGS2010

Observations of drainage network change in a recently burned watershed using terrestrial laser scanning

Wildfire enhances the geomorphic response of a watershed to precipitation events, effectively altering the form of the hillslope and channel drainage network. Typically, drainage networks expand following rainfall on a recently burned watershed. Expansion of drainage networks following wildfire increases in erosion and sediment transport rates, and the probability of flash-flooding and debris-flows at downstream locations. Observations of the response of hillslope and channel drainage to individual precipitation events are vital to unraveling the dynamics of erosion processes in recently burned watersheds. Here, we apply terrestrial laser scanning (TLS) methods to produce digital terrain models (DTMs) of a recently burned watershed at an unprecedented spatial resolution. The DTM data aid the quantification of changes in the hillslope and channel drainage networks at several spatial scales. Two TLS surveys were conducted, one survey between 28-30 September 2008 to document pre-rainfall conditions, and one between 18-21 December 2008, three days after 52 mm of rainfall over a period of 22 hours. A Leica Geosystems ScanStation 2 TLS was used to generate 1 cm resolution DTMs, from which the hillslope and channel drainage networks were derived. The location and magnitude of erosion and deposition for each pixel within the basin was determined by calculating the topographic differences between DTMs. Changes in the drainage network morphology were identified through the analysis of bifurcation ratio, drainage density (including rills), rill length, horizontal migration of rills, width-depth ratios and upstream migration of knickpoints. Comparisons of these measures were made between morphologically distinct sub-basins within the study area, and between surveys. Analyses of bifurcation ratios, and measures of rill position and gullyhead migration indicate an expansion of the rill network and upstream migration of knickpoints. These results suggest that expansion of the drainage network is a function of boundary conditions that exist at multiple spatial scales, including depth to bedrock, surface roughness, and contributing area. Additional predictive capability at this spatial and temporal resolution is going to require a physically-based model capable of combining high-resolution topographic changes and process information from in-situ measurements of flow dynamics.

Conference Paper↗
USGS1995

Magnitude and frequency of peak discharges for Mississippi River Basin Flood of 1993

The magnitude and frequency of the 1993 peak discharges in the upper Mississippi River Basin are characterized by applying Bulletin 17B and L-moment methods to annual peak discharges at 115 unregulated watersheds in the basin. The analysis indicated that the 1993 flood was primarily a 50-year or less event on unregulated watersheds less than about 50,000 km 2 (20,000 mi 2 ). Of the 115 stations analyzed, the Bulletin 17B and L-moment methods were used to identify 89 and 84 stations, respectively, having recurrence intervals of 50 years or less, and 31 and 26 stations, respectively, having recurrence intervals greater than 50 years for the 1993 peak discharges. The 1993 flood in the upper Mississippi River Basin was significant in terms of (a) peak discharges with recurrence intervals greater than 50 years at approximately 25 percent of the stations analyzed, (b) peak discharges of record at 33 of the 115 stations analyzed, (c) extreme magnitude, duration, and areal extent of precipitation, (d) flood volumes with recurrence intervals greater than 100 years at many stations, and (e) extreme flood damage and loss of lives. Furthermore, peak discharges on several larger, regulated watersheds also exceeded the 100-year recurrence interval. However, for about 75 percent of the 115 unregulated stations in the analysis, the frequency of the 1993 peak discharges was less than a 50-year event.

Transportation Research Record↗
USGS2008

Retrospective Review of Watershed Characteristics and a Framework for Future Research in the Sarasota Bay Watershed, Florida

The U.S. Geological Survey, in cooperation with the Sarasota Bay Estuary Program conducted a retrospective review of characteristics of the Sarasota Bay watershed in west-central Florida. This report describes watershed characteristics, surface- and ground-water processes, and the environmental setting of the Sarasota Bay watershed. Population growth during the last 50 years is transforming the Sarasota Bay watershed from rural and agriculture to urban and suburban. The transition has resulted in land-use changes that influence surface- and ground-water processes in the watershed. Increased impervious cover decreases recharge to ground water and increases overland runoff and the pollutants carried in the runoff. Soil compaction resulting from agriculture, construction, and recreation activities also decreases recharge to ground water. Conventional approaches to stormwater runoff have involved conveyances and large storage areas. Low-impact development approaches, designed to provide recharge near the precipitation point-of-contact, are being used increasingly in the watershed. Simple pollutant loading models applied to the Sarasota Bay watershed have focused on large-scale processes and pollutant loads determined from empirical values and mean event concentrations. Complex watershed models and more intensive data-collection programs can provide the level of information needed to quantify (1) the effects of lot-scale land practices on runoff, storage, and ground-water recharge, (2) dry and wet season flux of nutrients through atmospheric deposition, (3) changes in partitioning of water and contaminants as urbanization alters predevelopment rainfall-runoff relations, and (4) linkages between watershed models and lot-scale models to evaluate the effect of small-scale changes over the entire Sarasota Bay watershed. As urbanization in the Sarasota Bay watershed continues, focused research on water-resources issues can provide information needed by water-resources managers to ensure the future health of the watershed.

Open-File Report↗
USGS2011

Suspended sediment and organic contaminants in the San Lorenzo River, California, water years 2009-2010

This report presents analyses of suspended sediment and organic contaminants measured during a two-year study of the San Lorenzo River, central California, which discharges into the Pacific Ocean within the Monterey Bay National Marine Sanctuary. Most suspended-sediment transport occurred during flooding caused by winter storms; 55 percent of the sediment load was transported by the river during a three-day flood in January 2010. Concentrations of polyaromatic hydrocarbons can exceed regulatory criteria during high-flow events in the San Lorenzo River. These results highlight the importance of episodic sediment and contaminant transport in steep, mountainous, coastal watersheds and emphasize the importance of understanding physical processes and quantifying chemical constituents in discharge from coastal watersheds on event-scale terms.

Open-File Report↗
USGS2008

Debris flows and floods in southeastern Arizona from extreme precipitation in July 2006 — Magnitude, frequency, and sediment delivery

From July 31 to August 1, 2006, an unusual set of atmospheric conditions aligned to produce record floods and an unprecedented number of slope failures and debris flows in southeastern Arizona. During the week leading up to the event, an upper-level low-pressure system centered over New Mexico generated widespread and locally heavy rainfall in southeastern Arizona, culminating in a series of strong, mesoscale convective systems that affected the region in the early morning hours of July 31 and August 1. Rainfall from July 27 through 30 provided sufficient antecedent moisture that the storms of July 31 through August 1 resulted in record streamflow flooding in northeastern Pima County and eastern Pinal County. The rainfall caused at least 623 slope failures in four mountain ranges, including more than 30 near Bowie Mountain in the northern Chiracahua Mountains, and 113 at the southern end of the Huachuca Mountains within and adjacent to Coronado National Memorial. In the Santa Catalina Mountains north of Tucson, 435 slope failures spawned debris flows on July 31 that, together with flood runoff, damaged structures and roads, affecting infrastructure within Tucson’s urban boundary. Heavy, localized rainfall in the Galiuro Mountains on August 1, 2006, resulted in at least 45 slope failures and an unknown number of debris flows in Aravaipa Canyon. In the southern Santa Catalina Mountains, the maximum 3-day precipitation measured at a climate station for July 29-31 was 12.04 in., which has a 1,200-year recurrence interval. Other rainfall totals from late July to August 1 in southeastern Arizona also exceeded 1,000-year recurrence intervals. The storms produced floods of record along six watercourses, and these floods had recurrence intervals of 100-500 years. Repeat photography suggests that the spate of slope failures was historically unprecedented, and geologic mapping and cosmogenic dating of ancient debris-flow deposits indicate that debris flows reaching alluvial fans in the Tucson basin are extremely rare events. Although recent watershed changes—particularly the impacts of recent wildland fires—may be important locally, the record number of slope failures and debris flows were related predominantly to extreme precipitation, not other factors such as fire history. The large number of slope failures and debris flows in an area with few such occurrences historically underscores the rarity of this type of meteorological event in southeastern Arizona. Most slope failures appeared to be shallow-seated slope failures of colluvium on steep slopes that caused deep scour of chutes and substantial aggradation of channels downstream. In the southern Santa Catalina Mountains, we estimate that 1.5 million tons of sediment were released from slope failures into the channels of ten drainage basins. Thirty-six percent of this sediment (527,000 tons) is gravel-sized or smaller and is likely to be transported by streamflow out of the mountain drainages and into the drainage network of metropolitan Tucson. This sediment poses a potential flood hazard by reducing conveyance in fixed-section flood control structures along Rillito Creek and its major tributaries, although our estimates suggest that deposition may be small if it is distributed widely along the channel, which is expected. Using the stochastic debris-flow model LAHARZ, we simulated debris-flow transport from slope failures to the apices of alluvial fans flanking the southern Santa Catalina Mountains. Despite considerable uncertainty in applying coefficients developed from worldwide observations to conditions in the southern Santa Catalina Mountains, we predicted the approximate area of depositional zones for several 2006 debris flows, particularly for Soldier Canyon. Better results could be achieved in some canyons if sediment budgets could be developed to account for alternating transport and deposition zones in channels with abrupt expansions and contractions, such as Rattlesnake Canyon.

Arizona↗