Posts Tagged ‘runoff’

BMP’s and climate change

Tuesday, January 10th, 2012

February 2012 Article: “Sensitivity Analysis of Best Management Practices Under Climate Change Scenarios,” by Sean A. Woznicki and A. Pouyan Nejadhashemi.

“The results of this research suggest that the majority of agricultural BMPs tested in this study are significantly sensitive to climate change.” That ought to get your attention!

The objective of this study was to perform a sensitivity analysis of BMPs across future climate change scenarios for the Tuttle Creek Lake watershed (TCLW) of Kansas and Nebraska using Soil and Water Assessment Tool (SWAT) 2009 model. Eight agricultural BMPs and a baseline scenario were implemented within SWAT for each of four climate scenarios.

The results show too many details for a quick summary here. You’ll have to read the article to learn about any particular method. The lesson, though, is that BMP’s are sensitive to climate changes, and the effect varies for the particular BMP.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own.]

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A simple water balance model

Monday, January 2nd, 2012

February 2012 Article (Early View): “Prediction of Streamflow Regime and Annual Runoff for Ungauged Basins Using a Distributed Monthly Water Balance Model,” by R.D. (Dan) Moore, J.W. Trubilowicz, and J.M Buttle.

(I really love a good abstract, so I’m just going to copy this one here!)

Prediction of streamflow in ungauged basins is a global challenge, but is particularly an issue in physiographically complex regions like British Columbia (BC), Canada. The objective of this study was to assess the accuracy of a simple water balance model that can be run using existing spatial datasets. The model was developed by modifying an existing monthly water balance model to account for interception loss from forest canopy, glacier melt, and evaporation from lakes. The model was run using monthly climate normals from the ClimateBC application, which have a horizontal resolution of 400 m. Each ClimateBC grid cell was classified as forest, open land, glacier or water surface based on provincial scale digital maps of biogeoclimatic zones, glaciers, and water. The output was monthly mean runoff from each grid cell. These values were integrated within the catchment boundaries for streams gauged by the Water Survey of Canada. Annual runoff was predicted with modest accuracy: after updating the predicted runoff by interpolating errors from neighboring gauged streams, the mean absolute error was 25.4% of the gauged value, and 52% of the streams had errors less than 20%. However, the model appears to be quite robust in distinguishing between pluvial, hybrid, and melt-dominated hydroclimatic regimes, and therefore has promise as a tool for catchment classification.

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Colorado River runoff

Wednesday, October 19th, 2011

December 2011 article (early view): “TRENDS IN WESTERN U.S. SNOWPACK AND RELATED UPPER COLORADO RIVER BASIN STREAMFLOW,” by W. Paul Miller and Thomas C. Piechota.

Previous research by the authors hypothesized a change in the character of precipitation (i.e., the frequency and amount of rainfall and snowfall events) throughout the Colorado River Basin. In the current study, 398 snowpack telemetry stations were investigated for trends in cumulative precipitation, snow water equivalent, and precipitation events. Observations of snow water equivalent characteristics were compared to observations in streamflow characteristics. Results indicate that the timing of the last day of the snow season corresponds well to the volume of runoff observed over the traditional peak flow season (April through July); conversely, the timing of the first day of the snow season does not correspond well to the volume of runoff observed over the peak flow season. This is significant to water resource managers and river forecasters, as snowpack characteristics may be indicative of a productive or unproductive runoff season.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Snowpack trends

Tuesday, July 19th, 2011

August 2011 article (Early View): “Trends in Western U.S. Snowpack and Related Upper Colorado River Basin Streamflow,” by W. Paul Miller and Thomas C. Piechota.

This study investigates trends in daily measurements of Snow Water Equivalent (SWE) in the Western U.S.. These trends are compared to observed streamflow trends over the Colorado River Basin in an attempt to quantify the impact of changing precipitation characteristics to streamflow in the basin and to improve understanding of the linkage between snowpack and streamflow over the basin. Trends in precipitation from 398 snowpack telemetry (SNOTEL) stations spanning the Western U.S. are investigated. Then, trends in USGS streamflow stations spanning the Colorado River Basin are considered. Finally, corresponding trends in streamflow over Colorado River headwater basins are related to regional SNOTEL stations within the headwater basins to better understand the linkages between SWE and streamflow.

Based on daily SNOTEL observations, the length of snowpack season has shortened during this period of recent historic drought, and corresponds to below average aggregate April through July runoff in Colorado headwater river basins. Interestingly, there is a much stronger correspondence between runoff characteristics and the timing of the end of the snowpack season than correspondence between runoff characteristics and the timing of the beginning of the snowpack season.

Conclusion: As snowpack and precipitation characteristics change in the Colorado River Basin in response to climate change, water supply forecasters in the region may no longer be able to rely on past observations of basin hydroclimatology to aid in the development of water supply projections.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Seasonal Flushing

Friday, January 21st, 2011

February 2011 Article: “Seasonal Flushing of Pollutant Concentrations and Loads in Urban Stormwater,” by Kenneth C. Schiff and Liesl L. Tiefenthaler.

The goal of this study was to census stormwater concentrations and loads from an arid, urban watershed to quantify seasonal flushing. Samples were collected every 15 min during the 1997-1998 wet season from the Santa Ana River and analyzed for total suspended solids. Initial storms of the season generated event mean concentrations 3-10 times the event mean concentration of storms later in the season. Early season storms discharged only 6% of the annual volume, but influenced flow-weighted mean concentrations well past the midpoint of the wet season.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Glaciated Watersheds

Monday, January 17th, 2011

February 2011 Article: “Using a GIS Model to Identify Internally Drained Areas and Runoff Contribution in a Glaciated Watershed,” by Jacob A. Macholl, Katherine A. Clancy, by Paul M. McGinley.

Delineating watersheds is especially problematic in the Midwest where multiple glaciations have left a relatively flat landscape with many potholes, wetlands, and lakes topographically isolated from the drainage network. Identifying areas that generate runoff but do not contribute to a drainage network (e.g., drain to a closed depression) is necessary for correctly identifying the factors that affect water quantity and quality.

The overall goal of this study is to use the Potential Contributing Source Area (PCSA) model to identify the areas of a northwestern Wisconsin watershed physically capable of contributing runoff to the stream drainage network. A secondary goal of this study was to use the NRCS Curve Number (CN) method to evaluate whether runoff volumes are better estimated using the potential contributing areas rather than the entire catchment area.

Although numerous runoff producing events occurred during the study period, the rainfall was of insufficient depth for estimating runoff using the standard CN method. The distributed CN method of estimating runoff did provide runoff volumes for the independent events and were, in general, better estimated using the potential contributing areas than the entire catchment area.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Land cover and hydrologic indices

Wednesday, November 17th, 2010

December 2010 article: “Impact of 20 Years of Land-Cover Change on the Hydrology of Streams in the Southeastern United States,” by James F. Cruise, Charles A. Laymon, and Osama Z. Al-Hamdan.

The authors look at land-cover changes and hydrologic indices for 12 watersheds in the southeastern U.S. They conclude land-cover effects on hydrologic variables may be nuanced and can sometimes be only indirectly evident.

Land-cover changes for portions of Alabama, Georgia, and Tennessee were estimated for the years 1980, 1990, and 2000 using classified Landsat images, and associated with hydrologic indices for 12 watersheds in the region. Results indicate that several of the watersheds had undergone significant (>20%) reductions in agricultural land cover with a coincident increase in forested land. Change like this is a common occurrence over much of the eastern United States for a variety of reasons. The hydrologic response was determined in terms of four variables: mean annual streamflow, precipitation minus runoff, frequency of inundation, and duration of inundation.

Once again nature shows her complexity. You might think the changes would be pretty straightforward. However, attempts to correlate the hydrologic results with the land-cover changes were only partially successful. It was not possible to relate definitively changing streamflow indices with land-cover change on an individual basin scale due to other factors such as soil characteristics and unavoidable deficiencies in the land-cover classification (e.g., fixed time scales). Changes in hydrology coincident with land-cover change can be evident in more subtle indices such as frequency of inundation in addition to, or in lieu of, direct measurements of annual runoff.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Urban Drainage Networks Matter

Tuesday, August 24th, 2010

October 2010 Article: Analyses of Urban Drainage Network Structure and its Impact on Hydrologic Response, by Katherine L. Meierdiercks, James A. Smith, Mary Lynn Baeck, Andrew J. Miller

Urban flood studies have linked the severity of flooding to the percent imperviousness or land use classifications of a watershed, but relatively little attention has been given to the impact of urban drainage networks — including storm pipes, surface channels, street gutters, and stormwater management ponds — on hydrologic response. The authors demonstrate that drainage networks, like natural river networks, exhibit characteristic structures and that these features play critical roles in determining urban hydrologic response.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Modeling an Extreme Flood in Texas

Monday, August 23rd, 2010

October 2010 Article: Hydrologic Modeling of an Extreme Flood in the Guadalupe River in Texas, by Hatim O. Sharif, Almoutaz A. Hassan, Sazzad Bin-Shafique, Hongjie Xie2, Jon Zeitler.

"Flash Flood Alley"

One of the most flash flood prone areas in the U.S. is a region of South-Central Texas, called Flash Flood Alley (see figure) by local residents and weather experts. This dubious honor is the result of both climatic and geomorphic factors. In November 2004, a moist air mass from the Gulf of Mexico combined with moist air from the Pacific Ocean resulted in the wettest November in Texas since 1895. This paper examines the meteorological conditions that led to this event and applies a two-dimensional, physically based, distributed-parameter hydrologic model to simulate the response of a portion of the basin.

The study results clearly demonstrate the ability of physically based, distributed-parameter simulations, driven by operational radar rainfall products, to adequately model the cumulative effect of two rainfall events and route inflows from three upstream watersheds without the need for significant calibration. Results of simulation by the distributed model demonstrate the advantage of using quality-controlled radar products, which typically better characterize the spatial and temporal distribution of rainfall than rain gauges.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Residential Soil Disturbance

Monday, July 26th, 2010

August 2010 Article: Impact of Residential Soil Disturbance on Infiltration Rate and Stormwater Runoff, by Christopher J. Woltemade.

Digging into my old yard in Reston always was an adventure: I never knew what I’d find  – bricks, lumber, etc. — left over from my home’s construction in 1967. Construction practices clearly left something to be desired. This study in southern Pennsylvania confirms my own unscientific observation of a huge amount of variation in how residential lawns respond to precipitation.

Curve numbers and stormwater runoff were substantially higher for lots constructed post-2000 compared with lots built pre-2000 and for undisturbed soils, documenting the magnitude of possible error in stormwater runoff models that neglect soil disturbance. A failure to consider such soil disturbances may lead to substantial errors of under-prediction in rainfall-runoff models.

The solution ultimately comes down to local codes and practices: Limit the footprint of soil disturbance, using mechanical soil loosening and organic soil amendments at the time of construction, and apply long-term lawn and landscape maintenance to enhance infiltration.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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