Browsing by Author "Bhaskar, Aditi, advisor"

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Open Access
Assessing the use of dual-drainage modeling to determine the effects of green stormwater infrastructure networks on events of roadway flooding
(Colorado State University. Libraries, 2020) Knight, Kathryn, author; Bhaskar, Aditi, advisor; Arabi, Mazdak, committee member; Kampf, Stephanie, committee member
Roadway flooding occurs when a stormwater network does not have the capacity to drain all runoff generated by precipitation. Roadway flooding causes damage to infrastructure and property, risks to human health and safety, and disruptions to transportation systems. Green stormwater infrastructure (GSI) has been increasingly used to reduce stormwater input to the subsurface stormwater network, stormwater draining to urban streams, and to improve water quality. It is unclear how GSI interacts with surface runoff and stormwater structures to affect the spatial extent and distribution of roadway flooding. This interaction was explored using a dual drainage model with individual stormwater structures represented, fine spatial resolution, and bidirectional flow between the subsurface stormwater network and surface runoff. The model was developed using the Stormwater Management Model for PC (PCSWMM) in the urban watershed Harvard Gulch in Denver, Colorado. We examined how dual drainage modeling could reveal the effect of converting between 1% and 5% of directly connected impervious area (DCIA) in the watershed to bioretention GSI on the extent, depth, and distribution of roadway flooding. Results of the surface flooding model were generally co-located with resident reports related to flooding within the study area. Results show that even for 1% of DCIA converted to GSI, the extent and mean depth of roadway flooding was reduced for the duration of the simulation, and increasing GSI conversion further reduced roadway flooding depth and extent. We found diminishing returns in the roadway flood extent reduction per additional percentage of DCIA converted to GSI beyond 2.5%, whereas diminishing returns occurred beyond 1% conversion to GSI for mean roadway flood depth reduction. This work also examined the limitations to the accurate representation of roadway flooding due to incomplete input data, a lack of observational data for urban floods, GSI placement methods, and high computational demands. With future work to reduce limitations, detailed dual drainage modeling has the potential to better predict what strategies will mitigate roadway flooding.
Open Access
Hydrologic responses to urbanization in Denver watersheds and investigation of precipitation thresholds for streamflow generation in pre-development semi-arid rangeland
(Colorado State University. Libraries, 2021) Wilson, Stacy, author; Bhaskar, Aditi, advisor; Kampf, Stephanie, committee member; Green, Tim, committee member
Urbanization alters stream hydrographs and has been shown to have detrimental effects on water quality, stream morphology, and riparian ecosystem function. A thorough understanding of this alteration is crucial for effective and sustainable water management as communities in semi-arid areas continue to grow at an accelerated pace. However, the hydrologic response to urbanization in semi-arid rangeland environments has not been well documented. Using eight years of instantaneous flow data for twenty-one watersheds ranging in size from 1 to 90 km2 with impervious areas ranging from 1 to 47%, this study provides a comprehensive analysis of hydrologic alteration occurring with urbanization in the semi-arid area of Denver, Colorado, USA. Using a semi-automated method to identify 2,877 streamflow events, we analyzed event-based metrics of peak flow, runoff depth, runoff ratio, time to peak, and duration, in addition to precipitation threshold and number of streamflow events occurring in response to precipitation events and zero flow. We found that number of events and peak flow increased significantly with the fraction of impervious area (imperviousness), while duration, precipitation threshold, and zero flow decreased significantly with imperviousness. Runoff depth, runoff ratio, and time to peak either gave mixed results or did not vary significantly with imperviousness. Our results suggest that urban watersheds in semi-arid environments are more hydraulically efficient than their undeveloped counterparts, resulting in an increased number of streamflow events generated by smaller precipitation events, with a quicker delivery of runoff to receiving streams. This research also characterized the flow in West Stroh Gulch rangeland in Parker, Colorado through time-lapse photography in conjunction with climatological data. Our monitoring period was limited to one year in duration, while no streamflow events were observed throughout our study, suggesting the precipitation threshold to generate runoff in this undeveloped rangeland exceeds the largest rainfall events observed (30 mm depth and a 60-minute maximum intensity of 5 mm/hour). Our data provides important baseline information for future comparison as development in semi-arid areas rapidly progresses, contributing physical data useful for model calibration. Overall, this research makes an important contribution to understanding the streamflow response of grasslands and urban watersheds to precipitation in semi-arid environments.
Open Access
Managing developing landscapes for stormwater, water yield, and ecosystem services with data-driven approaches
(Colorado State University. Libraries, 2022) Choat, Benjamin, author; Bhaskar, Aditi, advisor; Sharvelle, Sybil, committee member; Kampf, Stephanie, committee member; Ross, Matthew, committee member
To view the abstract, please see the full text of the document.
Open Access
Non-perennial streamflow & geomorphic patterns in a semi-arid rangeland slated for development
(Colorado State University. Libraries, 2023) Poteet, Dixie L., author; Bhaskar, Aditi, advisor; Morrison, Ryan, advisor; Kampf, Stephanie, committee member; Grigg, Neil, committee member
Urbanization has widely recognizable impacts on stream morphology and flow patterns. Predicting and quantifying these impacts can be difficult, especially for non-perennial streams in semi-arid rangelands. Non-perennial streams tend to lack a historical baseline with complete records of streamflow presence and absence. A historical pre-development baseline allows for better consideration when making development and infrastructure decisions as well as post-development comparison to quantify urbanization-driven impacts. This project focuses on a non-perennial stream channel in West Stroh Gulch, located in Parker, Colorado south of Denver, U.S.A. A historically semi-arid rangeland area slated to undergo housing development in the next few years, West Stroh Gulch is a unique opportunity to establish a historical baseline for a non-perennial stream. Streamflow presence and absence was recorded at multiple locations along the stream network with time-lapse photography. Photo observations and precipitation data were reviewed to determine what storm events did, or did not, trigger a flow response. After over two years of stream channel monitoring, one precipitation event with a total depth of 92-mm and maximum 60-minute intensity of 50-mm per hour triggered streamflow. Additionally, a hydrodynamic model was built in SRH-2D to compare the impacts of predicted flows through a reach of interest. Topographic pre-development data and Storm Water Management Model (SWMM) generated peak flows were used to simulate impacts of different sized storms. Peak flows varied both by storm and development scenario: existing undeveloped, traditional centralized post-development detention, and post-development distributed detention. Boundary shear stresses were used to compare the different simulations. Overall, the pre-development existing scenario had the lowest flows shear stresses for the two smallest storm scenarios (water quality capture volume and 2-year storms). For the 5-, 10-, 50-, and 100-year storms, the proposed post-development scenarios that incorporated distributed detention had the lowest flows and shear stresses. The traditional centralized detention post-development stormwater strategy had the highest flows, shear stresses, velocities, and water depths for all storm sizes. The simulation results indicate that the post-development distributed detention strategy will be effective at reducing stream channel stresses and erosion for larger storm events.
Open Access
Response of municipal water use to weather across the contiguous US
(Colorado State University. Libraries, 2018) Opalinski, Nicole, author; Bhaskar, Aditi, advisor; Sharvelle, Sybil, committee member; Manning, Dale, committee member
Municipal water demand exhibits seasonal patterns in response to summer withdrawals for landscape irrigation, particularly in dry regions of the western US. Outdoor water use can account for more than half of annual household water use, and therefore is a critical aspect of urban water planning under scarcity. Water use for landscape irrigation is responsive to local weather changes and drought restriction policies and therefore is targeted by demand management programs. Previous studies estimate the impact of climatic, socio-economic, and landscape factors on residential water use, but commonly focus on a single municipality. This nationwide study identified the response of municipal water use to weather variables (i.e., temperature, precipitation, evapotranspiration) using monthly water deliveries for 230 cities in the contiguous US. Using city-level multiple regression and regional-level fixed effects models, we investigated what portion of the variability in municipal water use was explained by weather across cities, and also estimated responses to weather across seasons and climate regions. Our findings indicated that municipal water use was generally well-explained by weather, with median adjusted R2 ranging from 63 to 95% across climate regions. Weather was more predictive of water use in dry climates compared to wet, and temperature had more explanatory power than precipitation or evapotranspiration. Climate regions and seasons were found to have significantly different water use responses to weather. In regional-level models, we found that relative seasonality in water use across regions corresponds to water use responses to changes in temperature. In response to a 1⁰C change in monthly maximum temperature, municipal water use was shown to increase by 1.1 to 3.9% on average, with greater responses in cold, dry regions and during summer. Climate change and population growth amplify the importance of understanding the impact of climate on water demand in the context of urban water supply.
Open Access
Spatial arrangement of stormwater infiltration affects partitioning of subsurface storage and baseflow timing
(Colorado State University. Libraries, 2019) Choat, Benjamin, author; Bhaskar, Aditi, advisor; Bailey, Ryan, committee member; Ronayne, Michael, committee member
Urban stormwater management is using distributed facilities that treat stormwater near where it falls at an increasing rate. These facilities are often designed to infiltrate water that would have previously been conveyed overland. By directing water that would have previously made it to receiving streams very quickly via overland flow into subsurface flow paths, the soil moisture, groundwater, and stream flow regimes are altered. While these alterations may have significant implications for urban watershed management, there remains a lack of knowledge about how spatial arrangements of infiltration focused facilities may affect catchment scale water-balances, including subsurface storage and streamflow. In particular, little focus has been given to relating site-scale behavior with catchment scale response. This project used a physically-based numerical model, ParFlow, to investigate the relationships between spatial arrangements of infiltration facilities, subsurface partitioning of water between unsaturated and saturated zones, and baseflow response duration and timing. Our findings show that more spatially distributed infiltration facilities, as compared to spatially-clustered infiltration facilities, encourage greater unsaturated zone storage, less saturated zone storage, and more total subsurface storage in scenarios where surface ponding is not severe. Depth to water table beneath infiltration facilities was found to be the main driver of observed differences in partitioning of subsurface storage. In our lowest conductivity soil, silt, severe groundwater mounding was observed at steady-state with significant surface ponding. In a catchment with high permeability and diffusivity, baseflow response to precipitation was delayed in the clustered infiltration scenario compared to the distributed scenario. The clustered scenario resulted in more baseflow after longer inter-event durations but lower baseflow between sequential precipitation events with short inter-event durations. In the same catchment, antecedent moisture was shown to amplify sensitivity of baseflow response to clustered infiltration spatial arrangement. These results can be used to help guide decisions about spatial locations of stormwater infiltration facilities to meet urban watershed management goals such as increasing plant available water, increasing aquifer recharge, producing more consistent or dynamic baseflow, and quicker or more delayed baseflow responses to precipitation.