Integrated Coastal Groundwater Monitoring Program and Plan

Monterey County Water Resources Agency (MCWRA) | May 19th, 2019

California American Water Company (CalAm) is working to increase sustainability of their water supply portfolio to meet the long-term needs of customers in their

California American Water Company (CalAm) is working to increase sustainability of their water supply portfolio to meet the long-term needs of customers in their service area on the Monterey Peninsula. Accordingly, CalAm has proposed the Monterey Peninsula Water Supply Project (MPWSP). The MPWSP includes a desalination plant, distribution pipelines, aquifer storage and recovery and in-lieu use of desalinated water. Feedwater for the desalination plant would be from a seawater intake system consisting of slant wells constructed into the shallow aquifers at the coastal margin of the Salinas Valley Groundwater Basin (SVGB). The objective of the MPWSP is to meet CalAm’s long-term water demands and comply with state imposed regulatory requirements1. A MPWSP Test Slant Wells Study (HWG, 2017) was conducted to evaluate project effects and support preparation of a draft and Final Environmental Impact Statement/Environmental Impact Report (EIR/EIS) (ESA, 2017). CalAm has received a Certificate of Public Convenience and Necessity CPCN) for the MPWSP from the California Public Utilities Commission (CPUC)2. The EIR/EIS supported the CPUC decision. This document presents a proposed Coastal Monitoring Plan (Monitoring Plan) to continue observing the MPWSP effects, if any, on the SVGB.

Integrated Hydrologic Model of Pajaro Valley, Santa Cruz and Monterey Counties, California

U.S. Geological Survey (USGS) | September 5th, 2014

Increasing population, agricultural development (including shifts to more water-intensive crops), and climate variability are placing increasingly larger demands on avail

Increasing population, agricultural development (including shifts to more water-intensive crops), and climate variability are placing increasingly larger demands on available groundwater resources in the Pajaro Valley, one of the most productive agricultural regions in the world. This study provided a refined conceptual model, geohydrologic framework, and integrated hydrologic model of the Pajaro Valley. The goal of this study was to produce a model capable of being accurate at scales relevant to water management decisions that are being considered in the revision and updates to the Basin Management Plan (BMP). The Pajaro Valley Hydrologic Model (PVHM) was designed to reproduce the most important natural and human components of the hydrologic system and related climatic factors, permitting an accurate assessment of groundwater conditions and processes that can inform the new BMP and help to improve planning for long-term sustainability of water resources. Model development included a revision of the conceptual model of the flow system, reevaluation of the previous model transformed into MODFLOW, implementation of the new geohydrologic model and conceptual model, and calibration of the transient hydrologic model. The conceptual model identified inflows and outflows that include the movement and use of water from natural and human components. The groundwater flow system is characterized as a layered geologic sedimentary system through which downward flow is driven by the combined effects of the application of irrigation water at the land surface and the pumping of groundwater from deeper in the system. Overall, groundwater meets most of the agricultural demand in the initial part of the growing season, augmented by precipitation during wet winter and spring seasons. In addition, the amount of groundwater used for irrigation varies from year to year in response to climate variation and can increase dramatically in dry years. Data on agricultural pumpage is a major component of simulated outflow that was previously unavailable; therefore, a coupled farm-process model was used to estimate historical pumpage for Pajaro Valley by subregion (water-balance subregions) as well as the delivery of surface water to and from the Harkins Slough Aquifer-Storage-and-Recovery System (HS-ASR) and related Coastal Distribution System (CDS) since 2002. The new, integrated hydrologic model includes new water-balance subregions; delineation of natural, municipal, and agricultural land use; streamflow networks; regions of tile drains; and, the groundwater flow system. The redefinition of the geohydrologic framework and incorporation into the simulation revealed the importance of the confining units at the base of the alluvial deposits and between the upper and lower Aromas Sand for regional groundwater flow.

Integrated Regional Water Management: Stakeholder Perspectives

California Department of Water Resources (DWR) | April 18th, 2017

Integrated regional water management (IRWM) is the application of integrated water management principles at the regional level. IRWM brings local agencies and other stake

Integrated regional water management (IRWM) is the application of integrated water management principles at the regional level. IRWM brings local agencies and other stakeholders, with a range of water-related roles and interests, together to address water management needs collaboratively within self-identified regions accepted by the State. The practice of IRWM is rooted in the principle of regional control, recognizing that local and regional water managers and other stakeholders, working together in a collaborative, open, and transparent manner, are best suited and best positioned to manage water resources in their regions. Issues including limited groundwater and surface water supplies, drought, flooding, climate change, water quality, environmental degradation, aging infrastructure, economic constraints, recreation, and cultural considerations are addressed through coordinated and integrated actions. IRWM is helping California move away from a legacy of fragmented, divisive, conflict prone, and sometimes ineffective water management practices by supporting cooperation among agencies and other stakeholders. Integrated water management at the regional level: Helps provide for public safety. Supports a healthy economy. Supports ecosystem vitality. IRWM benefits accrue at the local and regional level, but also “roll up” to the state level, helping California meet its collective water management needs. When IRWM succeeds, California succeeds.  

Integrated Water Availability in the Conterminous United States, 2010–20, Chapter F of U.S. Geological Survey Integrated Water Availability Assessment—2010–20

U.S. Geological Survey (USGS) | January 15th, 2025

The following are the key points of this chapter:  At the national scale, water supply is much higher than human demand, but regions with lower water supply show sm

The following are the key points of this chapter:  At the national scale, water supply is much higher than human demand, but regions with lower water supply show smaller differences and greater potential for imbalances in supply relative to demand. Eight percent of the conterminous United States (CONUS) population (26.7 million people) live in areas with chronic stress from water-supply and use imbalances. The Southern High Plains, Texas, Central High Plains, and Mississippi Embayment hydrologic regions had the most widespread coverage of 12 digit hydrologic unit code (HUC12) watersheds with water stress from supply-use limitations. Several fish species of conservation concern have large proportions of their habitat range in areas with chronic imbalances between surface-water supply and human use. Streams with elevated nutrient concentrations greater than reference conditions were widespread across the CONUS. Limitation of ecological water availability occurred even in humid areas of the CONUS without water-supply and use imbalances, primarily because of flow alterations associated with urban areas, other land uses, and water-management and infrastructure. The California–Nevada, Southwest Desert, Central High Plains, Southern High Plains, Texas, Mississippi Embayment, and Florida hydrologic regions showed high or severe stress in multiple aspects of water availability. A high proportion of the population living in areas with water-availability limitations are considered to be socially vulnerable, although this is a small percentage of the total CONUS population. Companion chapters: U.S. Geological Survey Integrated Water Availability Assessment—2010–20, Chapter A Water Supply in the Conterminous United States, Alaska, Hawaii, and Puerto Rico, Water Years 2010–20, Chapter B Status of Water-Quality Conditions in the United States, 2010–20, Chapter C  Water Use Across the Conterminous United States, Water Years 2010–20, Chapter D  Climate Change and Future Water Availability in the United States, Chapter E   

Integrated Water Operations in California: Hydropower, Overdraft, and Climate Change

University of California, Davis (UC Davis) | July 16th, 2015

Several management and climate cases are evaluated with the updated CALVIN, a hydro-economic optimization model of California’s inter-tied water supply infrastructure.

Several management and climate cases are evaluated with the updated CALVIN, a hydro-economic optimization model of California’s inter-tied water supply infrastructure. Updates to the CALVIN model include new projected 2050 agricultural target demands and scarcity penalties, improvements to network-flow representation, especially agricultural, urban, and wildlife refuge demands, and extended surface and ground water hydrology, now covering an 82-year historical inflow hydrology. A new energy price scheme is applied to CALVIN, which incorporates hourly energy price variations into monthly CALVIN operations. Using one constant average price for a month underestimates hydropower revenue and overestimates pumping costs. Hourly-varying moving average prices improved representation of hydropower revenue without creating significant scarcities to agricultural and urban water users. Effects of ending long-term groundwater overdraft in the Central Valley are evaluated with several management cases using CALVIN. The cases include effects of Delta outflow and Delta exports from a “no overdraft” policy. The least cost overdraft that minimizes groundwater pumping and scarcity costs is calculated for the 82-year period. Prohibiting Delta exports result in severe water scarcities south of the Delta. Water operations are more economical when overdraft is ended with adaptations, such as more Delta exports, increased groundwater banking, and water trades, than historical operations with overdraft. Finally, climate change effects under a warmer and drier climate scenario are studied and results are compared to historical hydrology. A drier and warmer climate shifts the timing and magnitude of stream flows. Spring snowmelt decreases and winter flows increase. Modelled reduction in rim inflows averages about 28%. This warmer-drier climate increases water scarcities, but adverse effects can be diminished with water sales, higher Delta exports, more conjunctive use, and wastewater recycling. 

Integrating Storage in California’s Changing Water System

University of California, Davis (UC Davis) | November 13th, 2014

Surface water reservoirs provide water supply and flood management benefits by capturing water when available and storing it for use when needed. Surface reservoirs are c

Surface water reservoirs provide water supply and flood management benefits by capturing water when available and storing it for use when needed. Surface reservoirs are commonly operated more for seasonal or short-term inter-annual needs. Groundwater aquifers generally provide longer-term storage and a source of water and seasonal storage in areas where surface water is limited. This paper reviews the benefits and challenges of water storage in California’s evolving water system, and provides some quantitative insights from an integrated analysis of this system. Water storage should not be viewed as isolated projects. For today’s water management objectives and conditions, surface water and groundwater storage should be considered and analyzed as parts of larger systems or portfolios of actions that include a wide variety of water sources, types and locations of storage, conveyance alternatives, and managing all forms of water demands. Such an integrated, multi-benefit perspective and analysis is a fundamental departure from most ongoing policy discussions and project analyses. The pilot study described in this paper focused on water storage and concludes that ability to utilize additional water storage in California varies greatly with its location, the availability of water conveyance capacity, and operation of the system to integrate surface, groundwater, and conveyance facilities. At most, California’s large-scale water system could utilize up to 5-6 million acre-feet of additional surface and groundwater storage capacity, and probably no more, which would likely provide 50-150 taf/year of additional water delivery for each million acre foot of additional storage capacity alone. The water supply and environmental performance of additional storage capacity is greatest when surface and groundwater storage are operated together. The benefits, and likely cost-effectiveness, of coordinating surface and groundwater storage and conveyance operations greatly surpass the benefits of expanding storage capacity alone, greatly expanding water delivery increases to as much as 200 taf/maf of additional storage capacity. Because we did not quantify and compare the economic value and costs of water supply and other benefits of expanding storage capacity, we cannot yet say if particular expansions would be economically justified. Similarly, because we did not comprehensively analyze the environmental impacts of expanding storage capacity or specific storage projects, we cannot yet say if particular expansions would be environmentally justified. Further, this study does not consider reoperation of existing facilities, water demand management, changes in prioritization of water uses or rights, or other policy or regulatory actions that might change the ability to supply water demands using existing water storage capabilities.

Intensification of hydrological drought in California by human water management

American Geophysical Union (AGU) | January 25th, 2017

Interactions between snow cover and evaporation lead to higher sensitivity of streamflow to temperature

Nature Portfolio (Springer Nature) | December 4th, 2020

Estimates of potential evaporation often neglect the effects of snow cover on evaporation process. Here, we present a definition of potential evaporation that explicitly

Estimates of potential evaporation often neglect the effects of snow cover on evaporation process. Here, we present a definition of potential evaporation that explicitly accounts for landscapes that are partially covered by snow. We show that, in the presence of snowpack, our evaporation estimates differ from conventional methods that assume evaporation from a free water surface. Specifically, we find that conventional methods overestimate potential evaporation as well as aridity, taken as the ratio of atmospheric water demand to supply, in landscapes where snowfall is significant. With dwindling snow-cover, actual aridity increases, which could explain the reduction in streamflow with decreasing snowfall. We suggest that streamflow, and hence water availability, is more sensitive to temperature changes in colder than in warmer regions.

Interbasin water transfers in the United States and Canada

Nature Portfolio (Springer Nature) | January 13th, 2023

Interbasin water transfers (IBTs) can have a significant impact on the environment, water availability, and economies within the basins importing and exporting water, as

Interbasin water transfers (IBTs) can have a significant impact on the environment, water availability, and economies within the basins importing and exporting water, as well as basins downstream of these water transfers. The lack of comprehensive data identifying and describing IBTs inhibits understanding of the role IBTs play in supplying water for society, as well as their collective hydrologic impact. We develop three connected datasets inventorying IBTs in the United States and Canada, including their features, geospatial details, and water transfer volumes. We surveyed the academic and gray literature, as well as local, state, and federal water agencies, to collect, process, and verify IBTs in Canada and the United States. Our comprehensive IBT datasets represent all known transfers of untreated water that cross subregion (US) or subdrainage area (CA) boundaries, characterizing a total of 641 IBT projects. The infrastructure-level data made available by these data products can be used to close water budgets, connect water supplies to water use, and better represent human impacts within hydrologic and ecosystem models.

Investigating Runoff Efficiency in Upper Colorado River Streamflow Over Past Centuries

American Geophysical Union (AGU) | January 5th, 2018

With increasing concerns about the impact of warming temperatures on water resources, more attention is being paid to the relationship between runoff and precipitat

With increasing concerns about the impact of warming temperatures on water resources, more attention is being paid to the relationship between runoff and precipitation, or runoff efficiency. Temperature is a key influence on Colorado River runoff efficiency, and warming temperatures are projected to reduce runoff efficiency. Here, we investigate the nature of runoff efficiency in the upper Colorado River (UCRB) basin over the past 400 years, with a specific focus on major droughts and pluvials, and to contextualize the instrumental period. We first verify the feasibility of reconstructing runoff efficiency from tree‐ring data. The reconstruction is then used to evaluate variability in runoff efficiency over periods of high and low flow, and its correspondence to a reconstruction of late runoff season UCRB temperature variability. Results indicate that runoff efficiency has played a consistent role in modulating the relationship between precipitation and streamflow over past centuries, and that temperature has likely been the key control. While negative runoff efficiency is most common during dry periods, and positive runoff efficiency during wet years, there are some instances of positive runoff efficiency moderating the impact of precipitation deficits on streamflow. Compared to past centuries, the 20th century has experienced twice as many high flow years with negative runoff efficiency, likely due to warm temperatures. These results suggest warming temperatures will continue to reduce runoff efficiency in wet or dry years, and that future flows will be less than anticipated from precipitation due to warming temperatures.