18.2: Running Water

Introduction to California's Hydrology: Running Water and Landscape Dynamics

Running water plays a pivotal role in shaping landscapes across California. Streams and rivers not only erode and shape mountains but also deposit sediment in valleys, creating dynamic, ever-changing terrains. Simultaneously, geology significantly influences how water flows across the landscape. This section delves into the interplay between running water and the physical landscape, examining how precipitation, streams, drainage basins, and hydrologic regions define California’s hydrology.

Precipitation

Precipitation is a key driver of California's hydrological cycle, affecting the state’s water resources and shaping both ecosystems and human activities. Precipitation refers to any form of water—rain, snow, sleet, or hail—that falls from the atmosphere to the Earth's surface. In California, the timing, amount, and distribution of precipitation are critical factors that influence water availability and management.

California’s Mediterranean climate results in highly variable precipitation patterns, both spatially and temporally. The state experiences distinct wet winters and dry summers, with most precipitation occurring between November and March. During these months, storms from the Pacific Ocean bring rain and snow, often carried by atmospheric rivers-long, moisture-laden air currents that can result in intense rainfall and snowfall.

The state's diverse geography—coastal plains, mountain ranges, deserts, and valleys—also plays a key role in determining how much precipitation different regions receive. Coastal areas generally experience more rainfall than inland areas, while mountain ranges, such as the Sierra Nevada, receive enhanced orographic precipitation due to the lifting of moist air over elevated terrain. Figure 18.2.1 illustrates the spatial distribution of average annual precipitation across California from 1900 to 1960.

Precipitation in California plays a crucial role in replenishing surface water reservoirs, groundwater aquifers, rivers, and streams—the primary sources of freshwater for the state's residents, agriculture, and industry. Snowpack, in particular, is a critical component of California's water supply, serving as a natural reservoir that gradually releases water during the spring and summer months as it melts. The Sierra Nevada mountain range, with its extensive snowpack, serves as a major source of water for the state's rivers and reservoirs.

Figure \(\PageIndex{1}\): "Average Annual Precipitation of California (1900-1960)" by Cole Heap form data in the California Open Data Portal is licensed under CC BY-NC 4.0 Constructed in a GIS. View a detailed description of this image.

However, California's precipitation is highly variable and unpredictable, affected by climate change, natural climate cycles like El Niño and La Niña, and human activities. Droughts, floods, and extreme weather events create significant challenges for water management. Graph 18.2.1 provides an interactive look at California's annual precipitation from 1895 to 2021, demonstrating the extent of this variability.

Statewide Annual Precipitation (1895-2021)

Graph 18.2.1: Statewide Annual Precipitation (1895-2021) by the California Office of Environmental Health Hazard Assessment is in the public domain. This interactive image allows users to select plotted data by year.

Drainage and Runoff

Precipitation in California plays a crucial role in replenishing surface water reservoirs, groundwater aquifers, rivers, and streams—the primary sources of freshwater for the state’s residents, agriculture, and industry. A critical element in the movement of water is the concept of drainage basins, or watersheds, which are defined by the geographical areas that drain water to specific rivers and bodies of water. Figure 18.2.2 provides a visual example of how drainage basins are physically organized.

Drainage basins are essential for understanding how water flows across landscapes and their interconnectedness. They function as natural reservoirs, collecting rainwater and snowmelt, regulating streamflow, and contributing to groundwater recharge. Basin boundaries, known as watershed divides, are formed by topographical features like ridgelines and hills that dictate the direction of water flow. The complex interaction of runoff and infiltration within a basin influences both the timing and magnitude of streamflow. Is it any wonder as to how the underlying geology influences waterflow?

California’s landscapes exhibit a variety of drainage basin types due to its diverse topography. Mountainous areas like the Sierra Nevada contain elongated drainage basins that follow valleys, while flatter regions such as the Central Valley feature broad, interconnected basins. Coastal areas often exhibit dendritic patterns, while volcanic regions like the Cascades have radial basins that extend outward from central peaks. Video 18.2.1 provides further insight into the structure of drainage basins and watersheds.

Figure \(\PageIndex{2}\): Basic anatomy of drainage basins by edukemy from "Stream Basins" is licensed under CC BY-NC 4.0. View a detailed description of this image.

Video 18.2.1 - What is a Drainage Basin?

Video 18.2.1 "What is a Drainage Basin?" by Mr. Middleton is licensed under CC BY-NC 4.0. Access a written description.

Drainage basins vary in size, shape, and complexity, ranging from small, localized watersheds to vast, interconnected river systems spanning multiple states or countries. The size of a drainage basin is often described in terms of its drainage area, measured in square kilometers or square miles. Larger drainage basins, such as those of major rivers like the Mississippi or Amazon, can encompass millions of square kilometers and drain vast portions of continents.

The shape of a drainage basin is also influenced by the topography of the surrounding landscape, with basins typically conforming to the natural contours of the land. Basins in mountainous regions may be elongated and narrow, following the course of valleys and ridgelines, while basins in flat or gently sloping terrain may be more rounded or irregular in shape. In California, a state marked by diverse landscapes, a variety of drainage basin types can be found. The Sierra Nevada range features elongated deranged basins tracing the contours of valleys and mountain ranges. In the Great Valley, rectangular basins meander through the relatively flat expanse of agricultural lands. Along the rugged coastline of the Pacific Ocean, dendritic basins emerge amidst the coastal cliffs and hillsides, resembling branching tree patterns. In volcanic regions like the Cascades, radial basins emanate from central peaks, mirroring the spokes of a wheel. In regions with alternating bands of resistant and easily eroded rock, trellis basins form parallel valleys and ridges, creating a distinctive pattern across the landscape.

Activity - Types of Drainage Basins \(\PageIndex{1}\)

Streams and Sediment Dynamics

Fluvial environments, where water flows through channels, are another critical component of California’s hydrology. Streams transport water across the state, creating and reshaping landscapes as they erode mountains and deposit sediment in valleys. The nature of these streams varies widely, from the sinuous meandering streams to braided streams and straight channels.

Meandering Streams

Meandering streams are common in California’s lowland areas, where they form winding paths through the landscape. The Sacramento River, the longest river in California, is an excellent example of a meandering stream. Meandering streams are characterized by the continuous erosion of outer banks and sediment deposition along inner banks, forming point bars. This dynamic interplay between erosion and deposition helps shape the river’s course, creating a constantly changing landscape that provides diverse habitats for various plant and animal species. Figure 18.2.3 shows the river’s course through the Central Valley, where its meanders have shifted over time, creating oxbow lakes and fertile floodplains.

Figure \(\PageIndex{3}\): Sacramento River by the University of Oregon is in the public domain. View a detailed description of this image.

An oxbow lake is a U-shaped body of water formed when a wide meander from a river is cut off, creating a separate, isolated lake. This process occurs when the meander becomes extremely curved and the neck of the meander narrows, eventually causing the river to break through and take a more direct path. The abandoned meander loop, now cut off from the main flow of the river, forms an oxbow lake. Over time, these lakes can become rich in nutrients, supporting diverse aquatic habitats, but they may also dry up if they are not replenished by water from the river or precipitation.

Braided Streams

Braided streams are typified by their complex, intertwined channels, separated by sediment bars. These streams are common in areas with high sediment loads and variable flows. The Santa Clara River, shown in Figure 18.2.4, exemplifies this type of stream. Braided streams often present challenges for flood management and land use, as their shifting courses can alter channel locations over short timescales.

Figure \(\PageIndex{4}\): "Santa Clara River", CA from the air by Shannon1 is licensed under CC BY-SA 2.0. View a detailed description of this image.

In braided streams, sediment dynamics are characterized by the continuous deposition and reworking of sediment bars and islands. Sediment generally is coarse, forming obstacles for water to attempt to flow around. Flows divide and recombine as they encounter such obstacles, leading to lateral and vertical accretion, which can rapidly alter channel morphology. The shifting nature of braided streams presents challenges for land management and flood control, requiring adaptive strategies to mitigate risks while preserving ecological integrity.

Straight Channels

While less common, straight channels do exist in California's rugged terrain, especially in steep mountainous regions or areas affected by recent glaciation. In the alpine reaches of the Sierra Nevada, for instance, streams cascade down steep slopes, carving straight channels as they descend. These channels, though relatively short-lived in geological terms, showcase the erosive power of water in shaping mountain landscapes.

Activity - Streams in the Hydrologic Cycle \(\PageIndex{1}\)

California’s Hydrologic Regions

California is divided into ten hydrologic regions, each with unique geographic, climatic, and hydrological characteristics that influence water availability, quality, and management. These regions provide a framework for understanding California's diverse water resources and the challenges posed by varying landscapes, from coastal zones to desert basins. Figure 18.2.5 provides a visual overview of the state’s hydrologic regions.

Figure \(\PageIndex{5}\): "California Hydrologic Regions" by the California Department of Conservation is in the public domain. View a detailed description of this image.

70% of the groundwater used in the state comes from the Great Valley, 20% comes from the South Coast and Central Coast Hydrologic Regions, and the rest from the remaining hydrologic regions. It is estimated that agriculture uses 34 million acre-feet out of the total 43 million acre-feet available from surface and groundwater. To put that in perspective, one acre-foot is the amount of water needed to cover an acre of land (about the size of a football field) with one foot of water—enough to supply about two average households for a year. That means agriculture uses close to 79% of all available water in the state! The largest source of surface water comes from the Sierra Nevada snowpack melt, which provides an average of 15 million acre-feet of water. The state’s infrastructure is designed to capture this runoff and deliver it through the federal Central Valley Project and the Delta State Water Project.

Notably, many of California’s drainage basins have steadily declining groundwater levels. Overdraft, which occurs when water is pumped out of an aquifer faster than it can be naturally replenished through rainfall or snowmelt infiltration, is estimated to be between 1-2 million acre-feet per year. This over-extraction can lead to a drop in the water table, dry wells, reduced groundwater storage capacity, and even land subsidence. Although a comprehensive study has not been conducted since 1980, the introduction of the Sustainable Groundwater Management Act (SGMA) in 2014 has made local water agencies responsible for monitoring groundwater levels and managing the volumes being extracted.

Other significant issues that may be found in each hydrologic region concern water quality, lack of data for decision making, poor management of surface and groundwaters, and poor agency coordination. Video 18.2.2 shows examples and lends further insight to the complexity of water management in California.

Video 18.2.2 - Tracking California's Water

Video 18.2.2: "Tracking California’s Water" by the United States Geological Survey is in the public domain.

Each of California's hydrologic regions presents unique opportunities and challenges in water resources management, reflecting the state's diverse geography, climate, and socio-economic dynamics. From the snow-capped peaks of the Sierra Nevada to the arid deserts of the Mojave, these regions exemplify the intricate interplay between natural processes, human activities, and water management practices.

North Coast Region

Located along the rugged northern California coastline, this region encompasses the Klamath River drainage and extends into northeastern California. Characterized by dense forests, steep terrain, and some of the highest rainfall levels in the state, the North Coast Region supports diverse ecosystems and important fisheries. Major rivers, such as the Eel River and the Russian River, are critical to local agriculture, fisheries, and municipal water supplies. This region’s abundant water resources also support redwood forests and salmon habitats.

San Francisco Bay Region

Encompassing the iconic San Francisco Bay and its surrounding watershed, this highly urbanized region faces unique water challenges. The San Francisco Bay Region is home to a dense population and extensive urban infrastructure, which contribute to problems such as urban runoff, saltwater intrusion, and habitat degradation. The San Francisco Estuary, where freshwater from the Sacramento and San Joaquin Rivers meets the Pacific Ocean, is crucial for both ecological health and water supply conveyance, making this region vital for statewide water management.

Central Coast Region

Stretching from the San Francisco Peninsula to Santa Barbara County, the Central Coast Region features diverse landscapes, including dramatic coastal cliffs, fertile agricultural valleys, and rich marine ecosystems. Major rivers, such as the Salinas River and the Santa Maria River, are central to supporting the region's agriculture, which is heavily dependent on both surface water and groundwater resources. Groundwater depletion and saltwater intrusion are ongoing concerns in this region due to agricultural demands and limited precipitation.

Sacramento River Region

Centered around the Sacramento River, California’s largest river, this region forms the backbone of the state’s water supply system. The Sacramento River and its tributaries, including the Feather, Yuba, and American Rivers, drain the northern Central Valley and are crucial to the Sacramento-San Joaquin Delta, a key hub for both water conveyance and ecological health. The region supports extensive agriculture and urban areas while being vital for fisheries and flood control. Figure 18.2.6 illustrates the geographic extent of the Sacramento River Basin and its tributaries.

Figure \(\PageIndex{6}\): "The Sacramento River Basin" by the California Department of Conservation is in the public domain. View a detailed description of this image.

San Joaquin River Region

The San Joaquin River Basin covers roughly 16,000 square miles (~4, 100 square kilometers) and has been heavily managed through infrastructure projects such as the Central Valley Project. This region plays a critical role in California’s agricultural production, though water use has significantly altered natural river flows. Efforts such as the San Joaquin River Restoration Program aim to restore river flows and fisheries. The basin is fed by snowmelt from the Sierra Nevada, with the eastside tributaries, including the Tuolumne, Stanislaus, and Merced Rivers, being dominated by snowmelt runoff. Figures 18.2.7 and 18.2.8 provide detailed maps of the San Joaquin River Basin and its hydrologic features.

Figure \(\PageIndex{7}\): "The San Joaquin River Basin" by the California Department of Conservation is in the public domain. View a detailed description of this image.

Figure \(\PageIndex{8}\): "The San Joaquin Valley hydrology conceptual model" by the United States Geological Survey is in the public domain. View a detailed description of this image.

Tulare Lake Region

Historically home to Tulare Lake, once one of the largest freshwater lakes in the United States, the Tulare Lake Basin is now predominantly agricultural and faces challenges related to groundwater depletion and land subsidence. The region’s rivers, including the Kings, Kaweah, Tule, and Kern, drain into what was once the Tulare Lakebed, a natural depression in the Central Valley. This closed basin only overflows into the San Joaquin River during extremely wet years. Figure 18.2.9 shows the geographic extent of the Tulare Lake Basin and its main rivers.

Figure \(\PageIndex{9}\): "The Tulare Lake River Basin" by the California Department of Conservation is licensed under public domain. View a detailed description of this image.

North Lahontan Region

Covering the northeastern corner of California, the North Lahontan Region is part of the Great Basin Desert. This sparsely populated region is characterized by alkaline lakes, sagebrush scrublands, and limited surface water resources. The region's rivers, such as the Susan River, are small and do not contribute to outflows beyond the Great Basin, making water management focused primarily on local use.

South Lahontan Region

Encompassing parts of the eastern Sierra Nevada and the Mojave Desert, the South Lahontan Region features rugged landscapes and iconic desert ecosystems. High-elevation lakes and rivers, such as the Owens River and Truckee River, are central to the region’s hydrology. However, the region is also known for its history of water conflicts, particularly involving the diversion of water from the Owens Valley to supply the city of Los Angeles.

South Coast Region

The South Coast Region is one of California's most densely populated areas, including major metropolitan centers such as Los Angeles, San Diego, and Orange County. This region relies heavily on imported water from the Colorado River, the Sacramento- San Joaquin Delta, and local groundwater supplies to meet the demands of its urban populations, agriculture, and industry. Water management challenges in this region include limited natural water resources, groundwater overdraft, and saltwater intrusion into coastal aquifers. Extensive water infrastructure, including reservoirs, aqueducts, and desalination plants, plays a crucial role in maintaining the region's water supply. Despite the arid climate, the South Coast Region supports diverse ecosystems, including coastal wetlands and chaparral, though many natural water systems have been significantly altered by urban development.

Colorado River Region

Located in southeastern California, the Colorado River Region is defined by its hot, arid desert landscape and its reliance on the Colorado River for water supply. This region includes the Imperial and Coachella Valleys, which are vital agricultural areas dependent on irrigation from the Colorado River. The region faces numerous water management challenges, including salinity issues, overal location of the Colorado River's water, and environmental concerns such as the shrinking of the Salton Sea. Innovative water conservation programs, such as the lining of canals to reduce water loss, are critical to sustaining both agriculture and urban water needs in this region. The Colorado River’s flow into California is tightly controlled through a series of dams and agreements with neighboring states and Mexico, making the region's water management intricately connected to interstate and international agreements.

Connecting Water Basins, Regions, and Groundwater Resources

Throughout the rest of this chapter, we will continue to explore the hydrological and geological features of each region, focusing on how the distinct basins within California's hydrologic regions shape water availability, distribution, and management. These surface water basins not only define the flow and collection of water but also serve as gateways to the state's vital groundwater reserves. As we transition to the next section, we will examine how these same basins influence groundwater recharge, storage, and extraction. By understanding the interplay between surface and groundwater systems and adopting integrated water management approaches, we can work towards ensuring sustainable water resources for future generations and promoting resilience in the face of changing environmental conditions.

References

1. California Department of Water Resources. (1987). California water: Looking to the future (Bulletin 160-87, p. 122). Sacramento, CA.
2. California Department of Water Resources. (2020). California's Groundwater (Bulletin 118). Sacramento, CA.
3. California Department of Water Resources. (2009). California Water Plan Update 2009, Volume 1: The Strategic Plan, Chapter 3: Companion State Plans. Retrieved April 11, 2024 from https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/California-Water-Plan/Docs/Update2009/Volume_1_Strategic_Plan/Vol1_Ch03_Companion_State_Plans.pdf
4. California Department of Water Resources. (n.d.). Home. Retrieved April 11, 2024, from https://water.ca.gov/
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6. California Water Boards: Central Valley R5. (n.d.). San Joaquin River Basin (SWAMP). Retrieved April 11, 2024, from https://www.waterboards.ca.gov/centralvalley/water_issues/swamp/sanjoaquin_river_basin/
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