Showing papers by "Feifei Pan published in 2013"

Remote sensing of river stage using the cross-sectional inundation area-river stage relationship (IARSR) constructed from digital elevation model data

Abstract: Remote sensing of discharge and river stage from space provides us with a promising alternative approach to monitor watersheds, no matter if they are ungauged, poorly gauged, or fully gauged. One approach is to estimate river stage from satellite measured inundation area based on the inundation area – river stage relationship (IARSR). However, this approach is not easy to implement because of a lack of data for constructing the IARSR. In this study, an innovative and robust approach to construct the IARSR from digital elevation model (DEM) data was developed and tested. It was shown that the constructed IARSR from DEM data could be used to retrieve water level or river stage from satellite-measured inundation area. To reduce the uncertainty in the estimated inundation area, a dual-thresholding method was proposed. The first threshold is the lower limit of pixel value for classifying water body pixels with a relatively high-level certainty. The second threshold is the upper limit of pixel value for classifying potentially flooded pixels. All pixels with values between the first threshold and the second threshold and adjacent to the classified water body pixels may be partially flooded. A linear interpolation method was used to estimate the wetted area of each partially flooded pixel. In applying the constructed IARSR to the estimated inundation areas from 11 Landsat TM images, 11 water levels were obtained. The root mean square error (RMSE) of the estimated water levels compared with the observed water levels at the US Geological Survey (USGS) gauging station on the Trinity River at Liberty in Liberty County, Texas, is about 0.38 m. Copyright © 2012 John Wiley & Sons, Ltd.

Effects of harvest on carbon and nitrogen dynamics in a Pacific Northwest forest catchment

Abstract: [1] We used a new ecohydrological model, Visualizing Ecosystems for Land Management Assessments (VELMA), to analyze the effects of forest harvest on catchment carbon and nitrogen dynamics. We applied the model to a 10 ha headwater catchment in the western Oregon Cascade Range where two major disturbance events have occurred during the past 500 years: a stand-replacing fire circa 1525 and a clear-cut in 1975. Hydrological and biogeochemical data from this site and other Pacific Northwest forest ecosystems were used to calibrate the model. Model parameters were first calibrated to simulate the postfire buildup of ecosystem carbon and nitrogen stocks in plants and soil from 1525 to 1969, the year when stream flow and chemistry measurements were begun. Thereafter, the model was used to simulate old-growth (1969–1974) and postharvest (1975–2008) temporal changes in carbon and nitrogen dynamics. VELMA accurately captured observed changes in carbon and nitrogen dynamics before and after harvest. The interaction of hydrological and biogeochemical processes in the model provided a means for interpreting these changes. Results show that (1) losses of dissolved nutrients in the preharvest old-growth forest were generally low and consisted primarily of organic nitrogen and carbon; (2) following harvest, carbon and nitrogen losses from the terrestrial system to the stream and atmosphere increased as a result of reduced plant nitrogen uptake, increased soil organic matter decomposition, and high soil moisture; and (3) the rate of forest regrowth following harvest was lower than that after fire because post-clear-cut stocks and turnover of detritus nitrogen were substantially lower than after fire.

Remote sensing of river stage and discharge

Abstract: Accurate measurement of river discharge, the volumetric rate of water flow passing through a river’s cross section, is essential to water supply planning and management, reservoir management and control, hydropower generation, flood prediction and control, understanding the global water cycle, and other hydrological applications. It is costly, labor intensive, and time consuming to directly measure river discharge because of the irregular geometry of river cross sections and the high variation of flow velocity in space and time. Most rivers require a series of measurements of flow velocity in each subsection of the cross section to achieve one accurate measurement of discharge. To save cost, labor, and time, river discharge is usually inferred from the measurement of river stage based on the stagedischarge rating (SDR) curve. The river stage is the height of water surface above a nearby reference point. Even if this technique is used, field surveys that measure the river discharge and stage simultaneously are still needed in order to construct the SDR curve at a particular cross section. Moreover, the stagedischarge relationship varies with time because the erosion and sediment deposition processes occurring in river channels and riverbanks constantly alter the geometry of channels. Therefore, a periodic check of the SDR curves against the direct measurements is needed. This is yet another reason why maintaining river gauging stations is cost-, labor-, and time-intensive. Remote sensing of river stage and discharge from space provides us with a promising alternative approach for monitoring watersheds. Since the 1990s, significant progress has been made in remote sensing of discharge and river stage.1–4 One relatively simple approach is to estimate river stage and discharge based on satellite-measured inundation area. While it is simple, there are still three obstacles to be overcome to improve the effectiveness and applicability of this approach. First, is it possible to construct the inundation area – river stage relationship (IARSR) Figure 1. The inundation area – river stage relationship (IARSR) curve (red) constructed from multiple data points (dots) of inundation area versus water level derived from the 10m resolution digital elevation model (DEM) inside the predefined polygon near the US Geological Survey gauging station on the Trinity River at Liberty in Texas.