Using Radar Rainfall and a Distributed Runoff Model to Determine Potential Reservoir Water Storage Gains
The problem: inadequate water supplies in the Western United States and inefficient usage of joint use, flood control, and surcharge storage at existing Reclamation reservoirs.
We pose two research questions to investigate this problem:
* Can Reclamation increase potential water storage at existing reservoirs by reducing joint use, flood control and surcharge storage and thereby make more effective use of space in existing reservoirs?
* Can Reclamation store additional water in reservoirs during operational hydrologic events rather than passing flow volumes downstream?
The working hypothesis for this Science and Technology (S&T) Program research project is: "Reclamation can potentially increase water storage at existing reservoirs by reducing joint use, flood control, and surcharge storage." The general approach to answer the research hypothesis and questions is via hydrologic modeling and simulation techniques that use radar rainfall and a distributed runoff model.
Need and Benefit
Reclamation needs this research product to increase water storage and improve allocation decisions at reservoirs. There is potential to increase storage at existing reservoirs by a combination of:
* Raising the top of active conservation storage elevation
* Reducing exclusive flood-control pool storage
* Modifying joint-use storage
* Reducing the surcharge storage
For managers and stakeholders to make effective decisions on these issues that may change operations and designs at existing Reclamation facilities, they need technical data, analyses, and information.
This product is a technical tool that can be used by engineers and scientists to analyze reservoirs and reservoir systems for potential increases in water storage at existing Reclamation sites. The goal is to use the tool and then provide analyses and results to managers and operators so they can make informed decisions. The tool consists of two main components: processing algorithms to convert readily-available next generation radar (NEXRAD) radar reflectivity observations into useful rainfall fields and a distributed runoff model that uses the rainfall to predict runoff hydrographs.
This research does have potential for broad application across Reclamation. However, the research approach that will be used is to start with a specific location and generalize the tools for application Reclamation-wide. The initial site for testing the tools is within the Great Plains (GP) Region. The research ideas outlined in this proposal will first be applied the Fryingpan-Arkansas Project within the GP Region. It is anticipated that the product tools can readily be transferred and applied to the Colorado-Big Thompson Project. It is envisioned that subsequent applications can be done Reclamation-wide at individual reservoirs using project rather than research funding. The initial test application site is Pueblo Reservoir.
The main research-related contributions and benefits are to potentially liberate water and increase flexibility for Reclamation project water users. The proposed approach focuses on liberating potential storage space in Reclamation reservoirs. The ideas are to: (1) increase water storage; and (2) prevent or reduce reservoir releases and/or spills due to operational hydrologic events. Quantitative benefits, applied to a single reservoir, could potentially be quite large. For example, at Pueblo Reservoir, if Reclamation could eliminate the flood control storage (26, 991 acre-feet [AF]) and reduce the joint-use pool by one-half (33, 000 AF), we could potentially liberate about 60, 000 AF. If one assumes that the cost of project water is $100/AF, the potential cost savings in one year for this reservoir (if 10 percent of the water were available in the first year) could be about $600, 000 to $1, 000, 000. This research could help the S&T Program meet a goal to realize a 10:1 return on investment.
There are few existing capabilities available to Reclamation from either internal or external sources that answer these reservoir storage increase questions at all Reclamation-wide facilities, or for particular regions. The existing capabilities are limited and apply for very few Reclamation reservoirs. These locations are part of the National Weather Service river forecasting areas, such as the Sacramento River in California. The majority of Reclamation reservoirs are not covered by these models. These models are limited because they are not designed to answer reservoir storage allocation, but are used for forecasting stages on large rivers. If the proposed tools were unavailable, existing Reclamation rainfall-runoff models would be used. The consequences would be inaccurate hydrograph estimates as very sparse rain gauge data would be used instead of radar data. This end product will be an improvement over existing capabilities in two areas: improved rainfall estimates and improved runoff modeling using physically-based methods.
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