Browsing by Author "Venayagamoorthy, S. Karan, committee member"

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Open Access
Assessing irrigation canal seepage reduction using polymer sealants
(Colorado State University. Libraries, 2024) Lund, Ahmad Abdur Rehman, author; Scalia, Joseph, IV, advisor; Gates, Timothy K., advisor; Venayagamoorthy, S. Karan, committee member; Andales, Allan A., committee member
Irrigation canals around the world experience varying degrees of seepage losses, with several potential adverse consequences and influenced by numerous factors. A synthesis and interpretation of field seepage data from peer-reviewed literature (impact factor >1.5) on seepage measurement and control reveals several key insights: (i) seepage rates differ significantly due to diverse field conditions; (ii) the inflow-outflow method is the most reliable for measuring canal seepage in the field; and (iii) polymer sealants (PSs) offer a cost-effective alternative for reducing seepage in irrigation canals. Compared to conventional liners (CLs) such as concrete, geomembranes, or masonry, PSs are not only more affordable but also can be applied selectively, allowing for seepage when the surface water supply is sufficient and groundwater recharge is desirable. Studies show PSs can reduce seepage by 64% to 88%, while CLs achieve reductions of 53% to 95%, highlighting the potential of PSs for further research and application. However, best field application techniques for PSs, the uncertainty in evaluating effectiveness, and ambiguity in potential environmental impacts require more comprehensive investigation. The most widely researched PS for reducing canal seepage is linear anionic polyacrylamide (LAPAM), a synthetic polymer sealant (SPS). When applied to canal water, LAPAM forms flocs through cation bridging with divalent cations (Mg2+ and Ca2+) commonly found in canal water, which settle along the canal perimeter and reduce hydraulic conductivity. Observed seepage reduction from field trials of LAPAM that had been conducted prior to this study on three mid-sized canals (two in Colorado, USA and one in Sindh, Pakistan) using the recommended inflow-outflow method for seepage testing were analyzed. The average pre-LAPAM seepage rate was approximately 0.32 m/day, while the post-LAPAM rate dropped to 0.04 m/day, with results demonstrating seepage reductions between 69% and 100%. An uncertainty analysis of the pre- and post-LAPAM tests indicated an 85% probability that the seepage reductions were due to the LAPAM treatment. While LAPAM has proven effective, the long-term environmental impact of LAPAM treatment remains uncertain, underscoring the need to explore natural alternatives to synthetic polymer sealants. Biopolymer sealants (BPSs) were identified and evaluated through both laboratory and field experiments, designed to mirror the approach used with LAPAM. These experiments were conducted in triplicate (lab) and duplicate (field) to enhance confidence. In the lab, constant head saturated hydraulic conductivity (KSAT) tests simulated irrigation canal perimeter conditions. Five BPSs—pectin citrus (PC), cellulose hydroxyethyl ether (CHE), pullulan desalinated (PD), sodium alginate low viscosity (SALV), and xanthan gum (XG)—were initially tested and compared against LAPAM. The pre-and post-polymer KSAT values revealed that PC, PD, and XG achieved average reductions exceeding 40%, which was used as the threshold for further exploration. Subsequent testing under conditions more representative of irrigation canals identified XG as the most effective BPS. Alternative application rates were assessed, with 20 mg/L identified as the preferred concentration, as higher concentrations did not significantly enhance KSAT reduction. Long-term performance tests in the lab showed that XG, at 40 mg/L, can reduce hydraulic conductivity by over 90% for 9–10 months and by 60–70% over 1.5 months at 20 mg/L. These findings were validated using seepage tests in the field, where XG applied to a 3-km earthen canal reach at 20 mg/L reduced seepage by up to 63% over a month (at which time the canal was taken out of service). While the use of SPSs may still be justified for controlling canal seepage, this research shows that BPSs such as XG, have the potential to replace SPSs for canal sealing. However, further work is needed to optimize application methods and dosage rates, to better understand working mechanisms, to demonstrate long-term effectiveness, and to assess scalability across diverse field conditions.
Open Access
TREX-SMA: a multi-event hybrid hydrologic model applied at California Gulch, Colorado
(Colorado State University. Libraries, 2012) Halgren, James, author; Julien, Pierre Y., advisor; Kampf, Stephanie K., committee member; Gates, Timothy K., committee member; Venayagamoorthy, S. Karan, committee member
This dissertation describes a hydrologic model, Two-Dimensional Runoff Erosion and Export (TREX) Soil Moisture Accounting (SMA), created from adding the Sacramento Soil Moisture Accounting model (SAC-SMA) to the TREX surface hydrology model. TREX-SMA combines the capabilities of TREX as a distributed physical surface hydrology model with a conceptual rendering of infiltration and return flow as found in SAC-SMA. In order to form the hybrid, infiltrated water (computed as a distributed function on the surface) is aggregated as an input to a system of soil moisture accounting zones, underlying the entire watershed. In each model time step, TREX SMA releases baseflow from the accumulated infiltrated water according to simple transfer functions. Evapotranspiration (ET) losses from the soil moisture zones are computed based on potential ET demand and available water. As baseflow and ET are released between precipitation events, TREX SMA recovers capacity in the soil moisture zones. Based on the simulated recovery, the model then re-initializes the infiltration parameters of the surface model to prepare for the next event, allowing continuous simulation of multiple events. The capabilities of the TREX SMA model to continuously simulate soil moisture, infiltration, and rainfall-runoff are demonstrated with an application to multi-event modeling on the 30 km2 California Gulch watershed, near Leadville, Colorado, United States. Precipitation inputs are derived from measurements at a system of six precipitation and stream flow gauges providing ten-minute data for the summer of 2006. Eight major events were recorded during this time with runoff produced at all gauges. One additional event with partial watershed response was also evaluated for a total of 54 event hydrographs in the 50-day simulated series. Time steps in the simulation ranged between 2.0 and 4.0 seconds. Parameters for the surface hydrology were obtained from a prior calibration of TREX and were distributed across 34,000 grid cells based on the 30-meter United States Geological Survey (USGS) Digital Elevation Model (DEM). Parameters for the soil moisture zones were obtained from a-priori estimates used by the Arkansas Basin River Forecast Center of the National Weather Service (NWS) of the National Oceanographic and Atmospheric Administration (NOAA) in their real-time operational flood forecasting model for the Arkansas River. Using conceptual soil moisture states to re-initialize distributed infiltration parameters, the simulation results with TREX SMA improved relative to results from the unmodified TREX model with constant infiltration parameters. Model results are processed using gnuplot to create real-time hydrograph plots as the simulation progresses. Gnu R scripts produce real-time plots of simulated minus observed residual and statistical analyses as the simulation progresses. Statistics generated for each gauge include Nash-Sutcliffe, percent bias, absolute percent bias, Pearson correlation and modified Pearson correlation, and mean-squared error. These statistics were generated both for the entire simulation series and for each individual storm event. The gnuplot and R plots are produced using web-based technology for instantaneous sharing via the Internet. Model results such as surface and channel water depth are processed with GRASS GIS and KML scripts to create 2.5 dimensional, browseable animations overlaid on a Google Earth terrain. Statistical measures of the improvement of TREX SMA over TREX are presented in this dissertation. The overall accuracy, measured by the Nash-Sutcliffe coefficient, improved in four out of six gauges. Peak over-estimation was corrected in a majority of the 54 peaks evaluated. Implementation of the TREX SMA soil moisture accounting algorithm to re-initialize the infiltration parameters reduces the total absolute peak error from 180% to 135% of the observed peak flow rates. The Nash-Sutcliffe model efficiency improved over standard TREX simulations by 43%, 11%, 5%, and 10% at CG-1, CG-4, CG-6, and SHG09A.