Wupatki National Monument Stormwater Management Solution
Due to the flooding that occurred at Wupatki National Monument in August of 2018, as a result of an approximate 150-year storm event that led to heavy sediment runoff, the National Park Service (NPS) has enlisted our team to develop a solution to mitigate the damage caused by such events in the future. This project is to be covered with NPS emergency funding. The main structures in need of protection against future storm events include the Wupatki Monument itself along with the visitor center and its related maintenance buildings. However, the team also had to take other considerations into account such as park aesthetics and the feasibility of designing for such improbable storms when discussing alternatives. As requested by the NPS, the team had a number of objectives to complete throughout the semester. These objectives included a physical evaluation of the site with a site visit, developing an understanding of the park’s needs, an evaluation of all considered alternatives, and a schematic design of the chosen alternative.
- Reilly Greer
- Raquel Lucero-Schnell
- Ethan Kondo
- Andrew Maynard
- Forrest Gage Pilone
- Tyler Swick
- Kevin To
- National Park Service
Project Advisor: Dr. Bahman Rejai
Technical Advisor: Prof. Kristoph Kinzli, Prof. Jeff Holley
Thank you to all of our donors! And special thanks to Noah Buikema and Vernon Cody for their advice, consultation, and guidance.
Project Description, Scope, and Next Steps
Initially, the team recommended a detention pond/sedimentation basin combined with a water reroute channel to direct the flow away from the monument. After consultation with the client we moved forward with designing a detention pond that would act as a sedimentation basin and decided to forego the water reroute channel. The team used several mathematical models and design standards to determine the size and shape of the basin. We decided that designing for two basins would be more practical based on the area of the watershed. We have produced a design plan that will be further optimized by the National Park Service. We recommend further surveying of the site be conducted to determine whether the size or the basins can be reduced. The environmental impacts of the flow out of the basins should also be studied. Finally, we recommended the National Park Service determine whether planting native shrubbery could reduce the amount of debris picked up by runoff.
When approaching this problem, the team was required to provide multiple design options to the client that could all mitigate or solve the stormwater issue experienced by the visitor center. A site visit helped motivate the team and grounded them to the issue. During the trip, the team evaluated the soil types present and surveyed the main area of concern. The soil type was determined to be SP-SM soil. This type of soil is poorly graded sand with silt that is not ideal for building on; however, it is possible to compact this soil for construction. This determination was important as it allowed the team to determine construction feasibility for each design possibility. The site evaluation also provided a better understanding of the flow path of water off the mesa and how designs could be physically implemented to affect the flow.
With the site evaluation completed, the volume of water that would need to be mitigated had to be determined. The team used multiple design methodologies to evaluate the possible volume calculations. These equations include the rational method and Soil Conservation Service (SCS) curve number method. This would help rationalize the different volume calculations conducted.
The team created four design alternatives to present to the client. Four design options were presented to the client: detention basins, drain tile piping, a channel and check dam system, and building relocation. The option to combine any of these options was also presented, but each design iteration was completed separately when first presented. To weigh these designs based on client needs, a decision matrix was utilized and each design evaluated. From this matrix and client communication, it was determined that the design of a dry detention basin system to sit above the visitor center and control stormwater flow was the best solution. Going forward, the design was focused on a dry detention basin system with an outflow structure that could help control the flows affecting the visitor center during large storm events.
The acreage of the site, peak flow of the storm event, rainfall intensity, soil permeability, and other factors were considered when designing for the detention basins. The design was based on a 100-year storm event with a rainfall intensity of 1.83 [in/hr], in a dry but undeveloped landscape of about 47 acres. The rainfall intensity and acreage were values reported by previous investigations of the site, and they were kept for consistency and accuracy. Ultimately, the client agreed with the approach.
Different calculation methods to determine runoff, flow, and volume resulted in different volumes possible because each method relied on different parameters. The team determined the design volume by pursuing each of the calculation methods and determining which volume value was most feasible for the Wupatki site (Table 1).
Table 1: Detention Basin Volume Calculations
Resulting Volume (ft3)
SCS Runoff (Normal Conditions)
The chosen design volume of 120,000 ft3 was used to size the trapezoidal detention basins. In which two basins of the same dimensions were designed to have a cumulative volume of 144,802 cubic feet when a 1-foot freeboard was included. By utilizing two basins, management and maintenance is simpler due to reduced size, while allowing selective use if needed. A peak inflow of 48 cfs was calculated using the Rational Method, and that value was used to design the corresponding outflow systems. The design value accounted for the best fit data (Aspen Design) and the averaged volume while keeping a slightly higher safety factor and allowing for simplified dimensions. The excavated soil can potentially be used for the embankment on the basins; however, due to the soil type, it may not be the best option when considering the higher erosion factor. The site data previously collected was then used to determine basin placement on site.
There are common design rations for a trapezoidal detention basin. These include a 3:1 length to width ratio and a 4:1 horizontal to vertical slope ratio. The length to width ratio helps settle any loose soil or other particulates while the horizontal and vertical slope ratio stabilizes the basin walls. The team chose the basin to fully incorporate the entirety of the design volume to prevent any uncontrolled water from contacting the visitor center. A trapezoidal prism was used to gather preliminary dimensions for the bottom rectangle. To ensure an impermeable bottom, a clay foundation layer was chosen for the design. The other dimensions were determined in AutoCAD. Final dimensions for the two identical basins can be found in the gallery above. A profile for the basins can be found above as well.
A peak inflow of 48 cfs from the rational method was used to design the culvert outlet structure. To help size the culvert, the team used the Urban Control Flood Districts culvert design worksheet. The calculations and images relating to the culvert are in the gallery above. The pipe diameter was determined to be 30 inches with a peak outlet flow of 24 cfs. The basins will split the volume of water which allows for a smaller outlet flow, and therefore a lower risk and more manageable flow for the visitor center. The reduced flow will also reduce the sediment picked up by the water, reducing risk of sediment flow damage. A barrel length of feet was determined with a calculated headwater depth of 5.80 feet. The culvert completed the design goal of controlling the water outflow. A rip-rap bed stems from the culvert to help prevent any further erosion. The design aims to prevent damage similar to the 2018 storm, even in the case of full or overflowing basins. By locating the basins at the watershed’s natural outlet, water will accumulate in the designed ponds while simultaneously draining via a carefully designed culvert. The basins are appropriately designed to hold large volumes of water with an outstanding factor of safety provided by a 1 foot freeboard, making it extremely unlikely a storm will overflow the basins. Furthermore, the culvert was designed to drain a manageable volume at a slow enough velocity that will not significantly erode its surroundings or carry large amounts of sediment seen in the 2018 storm.
The design was evaluated in terms of cost using RSMeans cost estimator. The extended total cost of the project is 416,116.63 dollars. See gallery above for images of design and cost analysis.
Our team recommends building a more process-oriented analysis of the costs for the project. Additionally, the team would recommend surveying the entirety of the watershed with more effective and modern equipment. This would provide the client with a better understanding of the watershed, and it could potentially reduce the size of the basin and decrease the cost. The team also recommends designing a last-ditch prevention system. There is an opportune area before the visitor center area to build a small dike and reroute any water that surpasses the basin. The design should be evaluated to determine its environmental impact as well as the potential impact of the flow out of the basins. Lastly, the team suggests that further evaluation of the area is conducted to quantify the impact that planting local shrubbery could have on the amount of debris that is picked up by runoff.
Meet the Team
Reilly Greer is a senior majoring in environmental engineering. She will be continuing on to graduate school in pursuit of a master’s degree in hydrologic sciences and engineering. Outside of her studies, Reilly enjoys playing the viola, painting, and hiking. Though not a Colorado native, Reilly considers the state her home and hopes to spend many years here.
Ethan is a senior in environmental engineering here at Mines. He enjoys all things water, and hopes to one day get a career in it. He is a part of Mines Without Borders and played for the club volleyball team.
Raquel is a senior in mechanical engineering. She enjoys playing rugby, hanging out with friends, and taking pictures of her cat. She plans on pursuing a career in water energy, starting with getting her master’s at Mines.
Andy Maynard is a senior in mechanical engineering. He has a passion for construction and the outdoors. Working on a project like this is something he has always wanted to do.
Forrest Gage Pilone
Forrest Gage Pilone is an environmental engineering student who will graduate this May. After graduation, he will continue his studies at Mines and pursue a M.S. in civil and environmental engineering. He has a broad interest in environmental engineering and science, where he is most inclined to site assessment and remediation, hydrology, ocean systems, and water quality.
Tyler Swick is a senior undergraduate student in environmental engineering at the Colorado School of Mines. She spends her time on campus as an undergraduate research assistant on subsurface microbial projects in the Mines G.E.M Lab. As a Colorado native she enjoys hiking, fishing, and being outdoors in all the amazing landscapes the state has to offer.
Kevin To is a senior majoring in environmental engineering with a minor in sustainability studies. Kevin will be continuing on to graduate school in pursuit of a master’s degree in hydrologic sciences and engineering. Outside of his studies, Kevin enjoys boxing, rock climbing, and reading.