The Idaho Water Users Association (IWUA) midyear meeting in June highlighted significant water management challenges and innovative solutions in the Treasure Valley.
Speakers Mike Meyers, watermaster for Water District 63 (WD63), and Michael Schubert, a water resources engineer with HDR Engineering, focused on critical issues surrounding the Boise River and discussed the Treasure Valley Water Supply Project, which aims to better understand and manage return flows to the river.
"One of the main causes, we believe, for the decline in the drain flows is urbanization,” Meyers said. “[The Treasure Valley] is just getting gobbled up by houses."
Schubert added, "Certainly, water is reaching a transition in the Boise Basin. We've talked about urbanization, but along with that, you have changes in irrigation practices, from traditional flood irrigation to sprinkler irrigation."
To provide context on this issue, the Treasure Valley's irrigation systems were constructed between 1860 and 1900, with irrigation districts forming in the subsequent decades. By the early 20th century, rising water tables led to waterlogged lands, prompting the construction of drains to lower the water table. These drains became integral to the valley's water management, returning excess water to the Boise River.
Referring to these drains as the area’s “Thousand Springs,” Meyers emphasized their importance to the Treasure Valley. Historically, surface water deliveries have relied on drain return flows, contributing approximately 240,000 acre-feet of water below Caldwell. However, recent changes to the Treasure Valley landscape have significantly diminished these flows, with the decline reaching critical levels in 2021 and 2022.
"Flows on the Boise River dropped below the point where we could actually deliver water," Meyers said. "Meaning there was less deliverable water in the river to meet demand. And, if it hadn’t been for flow augmentation water in the river, we would have dried the river up below Caldwell."
In response, WD63 initiated a real-time monitoring project for every diversion on the Boise River, improving water administration and providing valuable data. On June 30, 2022, the district conducted an in-depth analysis of the drains to identify the most affected areas, discovering that the Mason Creek and Middleton drains, located in heavily urbanized areas, were primary contributors to reduced flows.
Currently, WD63 is leveraging data collection, automation and advanced analytics. The goal is to understand the changes in drain flows and facilitate collaboration among stakeholders. Meyers said, "The main objective of this study is to avoid additional administration and possible curtailment of water rights within the Boise River Basin by improving data collection and water management on the drains. We also want to better understand what impacts are more significant – urbanization or changes in irrigation practices."
This work has already identified the opportunity to improve water management by creating a regulation pond to mitigate fluctuations in Fifteen Mile Creek, a tributary to the Boise River. Through this project, WD63 aims to provide a more stable water flow in the Boise River and improve water delivery, security and reliability in the region.
Phased approach to water management
The project has three phases, with phase one well underway and phase two and three in initial stages:
- Phase one: Focuses on automation and data collection. The district has installed telemetry systems to monitor drain flows and diversions, providing real-time data that helps understand current water dynamics.
- Phase two: Involves developing analytical tools to project future drain flows. Using the collected data, the district aims to model the impact of urbanization, irrigation changes and groundwater fluctuations on future water availability.
- Phase three: Focuses on managing and mitigating the hydrologic impacts through outreach and collaboration, engaging with stakeholders to ensure coordinated efforts in water management.
Phase one data was used to calculate ungaged gains or losses between different Boise River gages, revealing a significant decrease in flow between Middleton and Caldwell from 2017 to 2023. Specifically, between 2021 and 2022, there was a 150-200 cfs (cubic feet per second) reduction in ungaged gain. This, paired with a nearly 150 cfs less in gaged returns to the river, indicates around 300 cfs less flow in the Boise River at Caldwell. To address this, additional gages have been added to drains between Middleton and Caldwell to better measure return flows to the Boise River.
Moving forward
As the Treasure Valley continues to urbanize, understanding the specific impacts of these changes on drain flows is essential. The district is working with Boise State University to analyze the influence of urbanization and climate on irrigation drainage. Preliminary findings indicate that increased urbanization does in fact decrease drain flows, a trend that needs further exploration to identify all contributing factors.
"This project is key in understanding how drain flow in the Treasure Valley will continue to evolve with urbanization," Schubert said. Developing a comprehensive hydrologic model that includes surface water elements alongside the existing groundwater model is crucial. This integrated approach will allow the district to project future water flows and make informed decisions to ensure water security and reliability in the Treasure Valley.
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