A well-functioning watershed provides clean water for drinking and irrigation, healthy soils, flood protection, habitat for wildlife, and outdoor recreation opportunities. Addressing these multiple issues calls for taking a watershed management approach.
No matter where you are in the world, you are in a watershed. The water flowing over the land and through the soil creates a complex network that connects the uplands, springs, wetlands, streams, and rivers of the watershed. A well-functioning watershed provides clean water for drinking and irrigation, healthy soils, flood protection, habitat for wildlife, and outdoor recreation opportunities.
However, managing land and water for selected products or services has altered the conditions and functions in many of California’s watersheds. How land is managed within the watershed affects rainwater infiltration and the timing and volume of runoff. Human development within the watershed increases the amount of dissolved nutrients in the streams and waterways, often the result of fertilizers or biosolids, which can trigger dramatic changes in water bodies, vegetation, and wildlife communities. Many projects built before modern environmental laws have disrupted wildlife migration corridors and destroyed or degraded habitat that is critical for certain animal life stages. Active suppression of wildland fires since the 1920s has created an increased risk of larger, more intense wildfires that do more damage to watersheds than fires of historical intensities. And the watershed will be affected by changes in temperature, preciptiaton, and water flows that are projected to occur with the changing climate.
Addressing these multiple issues calls for taking a more holistic approach. Watershed management refers to the process of implementing land use and water management practices to protect water quality and other natural resources within the watershed by managing the use of land and water resources in a comprehensive manner. The primary objective of watershed management is to increase and sustain a watershed’s ability to provide for the diverse needs of the communities and stakeholders that depend on it.
WHAT IS A WATERSHED?
Historically, watersheds were defined as the divide between two drainage basins that separates the runoff from precipitation into one basin or the other, but in recent years, the term has been come to be applied to the entirety of the basin and not just the divide. NOAA defines a watershed as the land that channels rainfall or snowmelt to creeks, rivers, streams, lakes, and eventually to outflow points such as surface reservoirs, bays, estuaries, and the ocean.
A watershed includes all the natural and man-made features, including surface and subsurface features, climate and weather patterns, geologic and topographic history, soils and vegetation, and land use. A watershed can be a small area or as large as the Sacramento-San Joaquin basin. Smaller watersheds are sometimes referred to as catchments; large river basins are sometimes called drainage basins.
COMPONENTS OF A WATERSHED
There are many watershed attributes and processes that impact both water quantity and quality in the watershed. The relationship between the volume of water that enters a watershed and the volume available in the lakes, rivers, and streams is affected by the storage capacity and transport within the watershed, which in turn is determined by the evapotranspiration, percolation, losses to groundwater, and water diverted for human use.
Those components include:
Rivers and streams: Rivers and streams are usually described in terms of “stream order”, a designation of relative size. Streams can range from a first-order stream which are the smallest and have no tributaries to a 12th-order stream, which is the largest. There are a number of parameters that vary according to stream order, such as the relative abundance of species, nutrient and oxygen concentrations, the composition of the substrate, and velocity. Click here to learn more about stream order.
Lakes and reservoirs: Lakes and reservoirs are often used as water supply sources, receiving water from all other sources in the watershed, such as precipitation, runoff, discharges from tributaries, and upstream reservoir releases, and consequently, the water quality in the lakes and reservoirs is generally indicative of the condition of the watershed.
Topography: The topography is the physical surface of the watershed and includes both natural and manmade features. Topography is often described in terms of slope, aspect, and elevation which affect the movement, storage, and quality of water in the watershed. Topography also affects factors such as the intensity of solar radiation, the amount of precipitation and runoff, evaporation, sediment, and the type of vegetation present.
Geology and geomorphology: Geology is the composition, structure, and physical characteristics; geomorphology refers to the processes and mechanisms that created the geologic features. This is important for understanding things such as the relative composition of ionic constituents, conductivity, the permeability of the streambed, and sediment transport and deposition.
Soil: The composition of soil in the watershed determines how much rainfall or irrigation water will be retained in the soil gradually percolate downward, or whether it will add to surface water runoff and lead to increased erosion. Soil also influences the type of vegetation in the watershed.
Vegetation: Vegetation is important for intercepting runoff and allowing some or all of it to filter into the soil or return to the atmosphere through evaporation. Vegetation also improves water quality by stabilizing soils, absorbing nutrients, and filtering out sediment before the runoff reaches the river or stream.
Wildlife: The wildlife in a watershed can affect water quality and is sometimes associated with an increased potential for pathogens.
Land use: Land use can have a big impact on water quality. Land use activities include “working landscapes” or areas managed for agriculture or timber harvest; urban and residential areas; publicly and privately owned lands, and reserves.
PROTECTING WATER QUALITY IN THE WATERSHED
Both people and wildlife depend on the water in a watershed, but in order for this water to be useable for drinking, irrigation, transportation, and recreation, it has to be of good water quality, which is determined by certain physical, chemical, and biological characteristics of the water such as temperature, dissolved minerals and constituents, or the amount of pathogens that are present.
Sources of pollution in a watershed can be classified as either point source or nonpoint source pollution. Point sources are those that discharge to waterways directly from a pipe or other conveyance, such as the discharge of treated wastewater from a sewage treatment plant or a landfill. Businesses and industries often use hazardous materials in manufacturing or maintenance that are discharged from their operations and can contain solvents, petroleum products, of heavy metals. Point sources are regulated by federal and state agencies under the Clean Water Act through the issuance of permits that limit the types and amounts of pollutants a facility can discharge. There are also other laws and regulations that mandate the ways that hazardous materials are handled, stored, and used.
These laws, regulations, and voluntary efforts have helped clean up major water quality problems by reducing the amount of pollutants directly discharged to surface water and groundwater; however, about one-third of the nation’s waters are still not meeting water quality standards, and nonpoint sources of pollution have been identified as the primary culprit.
Non-point source pollution does not come from a specific source. Instead, it originates from many places, or from a widespread area, such as urban stormwater runoff or agricultural fields. It is often difficult to trace the exact origin of these pollutants because they result from a wide variety of human activities on the land as well as natural characteristics of the soil, climate, and topography. Nutrients, microorganisms and toxics are some of the most common contaminants, as is sediment, which can contaminate drinking water supplies or silt in spawning grounds for fish and other aquatic species.
During precipitation events, water quality is usually impacted because as rain flows over impervious surfaces such as pavement or roofs, it can’t soak into the ground so instead, the water flows across the landscape, picking up any trash, debris, pet droppings, pesticides, oils, and other contaminants along the way and dumping it all into the nearest waterway. The first rain of the season, usually after several dry months, is especially toxic and can be particularly problematic for water quality and aquatic life in urban streams.
And it’s not just surface water quality that is impacted – groundwater can be impacted as well. The ability for these pollutants to reach surface water or groundwater is enhanced by the amount of water available from rain or irrigation.
Stormwater can also dump large amounts of nutrients from garden fertilizers, decaying organic matter, and pet waste into waterways. While small amounts of nutrients such as nitrogen and phosphorous can be beneficial for aquatic plants, too many nutrients in the water can lead to poor water quality and in turn, lead to outbreaks of harmful algal blooms. During extreme weather events, heavy rainfall or snowmelt can even overwhelm the systems designed to collect stormwater, domestic sewage, and industrial wastewater, causing the sewer system to overflow into nearby bodies of water.
However, there are components of a watershed that work to improve water quality, such as trees and other vegetation that naturally filters out soil and sediment.
WATERSHED PLANNING AND MANAGEMENT
Historically, management of the environment has focused on specific issues such as air pollution or water quality, and these efforts have resulted in significant successes such as decreased air pollution, cleanup of contaminated groundwater, protection of species, and best management practices to control contaminant runoff. However, water quality impairments persist, a result of nonpoint source pollution and habitat degradation, which are complex problems that can cross multiple agency jurisdictions and responsibilities. Tackling these problems means stakeholders must come together to better understand the different facets of the problem and the actions that can be taken to improve conditions in the watershed.
Watershed management is the process of developing and implementing programs and projects to restore, sustain, and enhance the watershed functions that provide the services and values desired by the residents of the watershed. The primary objective of watershed management is to sustain and increase the watershed’s ability to provide for the needs of the community that depends on it, including the local, regional, state, federal, and tribal stakeholders. Community-based watershed management has emerged as the most effective framework for protecting water resources as these organized efforts serve as forums to bring together diverse stakeholders into a process that can benefit all of the participants.
Watershed planning and management focuses on the whole watershed in order to protect both water quality and water quantity. Effective management recognizes all of the mutually-independent interactions of the various elements of the watershed system, including the hydrologic cycle, nutrient cycling, energy flows, geologic characteristics, and ecology, as well as the role of large scale disturbances, such as flood or fire.
Planning and managing on a watershed scale produces numerous benefits, such as more reliable water supplies, lower water treatment costs, reduction of flood risk, drought mitigation, protection of habitat, nutrient cycling, carbon sequestration, maintaining biodiversity, and recreational opportunities. These are often referred to as ecosystem services.
The watershed planning process involves a number of activities that include identifying priority problems in the watershed, promoting a high level of involvement by all stakeholders, developing solutions, and measuring success through monitoring and other data gathering. The goal of watershed management is to plan and work toward an environmentally and economically healthy watershed that benefits all that have a stake in it.
ONE STEP FARTHER: INTEGRATED REGIONAL WATER MANAGEMENT
Integrated Regional Water Management (or IRWM) is an effort by the Department of Resources to support the implementation of water management soltuions on a regional scale that increase regional self-reliance, reduce conflict and manage water to concurrently achieve social, environmental, and economic objectives. IRWMs integrate all facets of water management including supply, water quality, wastewater, recycled water, floodwaters, and stormwater management.
Integrated planning involves local agencies, interest groups, and stakeholders who work together to coordinate planning activities across jurisdictional boundaries to achieve mutually beneficial solutions. This approach delivers higher value for investments by collaboratively developing sustainable solutions that provide multiple benefits including improved water quality, restored and enhanced ecosystems, resilient forests, better flood management, and more reliable surface and groundwater supplies.