STATE OF THE WATERSHED

The Upper Truckee River is the largest tributary and contributor of sediment and algal inducing nutrients flowing into Lake Tahoe.

The river starts high in the Tahoe National Forest in the Meiss Meadow area and draws water from Dardanelles Lake. Except for disturbances from cattle grazing, the river flows into the Lake Tahoe Basin through relatively pristine national forest land.

After reaching the developed neighborhoods at Christmas Valley, the river's health begins to deteriorate. Impacts from erosion, pollutants and loss of natural wetlands are the result of construction of homes and businesses along the river, large bridges such as on Highway 50, the Lake Tahoe Golf Course, the Lake Tahoe Airport, historic and current grazing and construction of the Tahoe Keys.

The result is an increased flow of fine sediment, nitrogen and phosphorus to Lake Tahoe,  which contributes to algae growth and loss of water clarity.

In the project area, the river has been impacted by channel straightening, (probably in the 1930s), which led to increased slope and erosion.  This in turn caused the river to downcut and become disconnected from its floodplain.

 

Due to the incision, the meadow "sponge" was no longer refilled and water levels in the ground were lowered.  The meadows and riparian areas became dry, degrading the habitat.  The stream banks got taller as the stream downcut. They began to eroded at an accelerated pace, introducing sediment into the stream and ultimately to Lake Tahoe .

 

In the late 1950s prior to park ownership, a golf course was 

developed on the degraded meadow along the river. Washoe Meadows State Park (WMSP) and Lake Valley State Recreation Area (LVSRA), which includes the golf course,  were obtained by California state parks in 1984.  The river is still suffering from high rates of erosion and is surrounded by golf course infrastructure.  Both of these contribute to habitat and water quality degradation

In addition to current impacts, the river bears the scars of years of alteration and uses within its 54-square-mile watershed.

HISTORIC USES

Logging

The period of Comstock logging, from about 1860 to 1890, resulted in widespread land disturbance that likely affected the river.  Several direct modifications of channels occurred during this period, including the construction of small dams to run mills and splash dam to provide water to float logs down the river.  Splash dams were generally 10 to 20 feet high timber or earthen structures designed to create a small ponds or lakes. 

 

They were designed to be destroyed at the height of runoff in the spring, typically with explosives.  The resulting flood helped carry logs to the lake.  The highly sinuous historic channel probably didn't float the logs very well. Crews likely had to dredge and modify the channel to salvage logs that got caught up and remove natural log jams to improve channel transport efficiency. 

 

It is likely that meanders were straightened to improve log-transport efficiency.  These operations increased erosion of the channel and had sever impacts on habitat.

Comstock logging also had pervasive watershed effects.  Loss of trees and compaction of soils led to increased runoff.  Soil disturbance resulted in increased erosion and sediment supply.  

Ranching and Farming Operations

All meadow areas have been grazed since the latter part of the 1800s.  The primary type of grazing has been cattle for dairy operations, although some grazing for horses and other ranch stock occurred.  In some areas, the channel was probably modified to reduce the impacts of floods on adjacent pastures (small levees, meander cut-offs).  

Channelization to improve agriculture operations and decrease flooding has occurred through the lower reach of the river.  Within the project area, the river was channelized just prior to the 1940 photos. 

 

Dredging and rip-rap have occurred in several locations since that time.  The small tributary from the south was also channelized prior to 1940.  Woody debris was probably also removed during channelization to improve flow capacity.

Adjacent meadows have been modified either for drainage or irrigation.  Angora Creek has been highly modified in the area of the confluence with the river.  It originally entered the river just upstream of the Elks Club-Highway 50 crossing. Sometime before 1940, it was channelized into a bend of the river about 2,000 feet further upstream. 

This was likely done to dry out the lower meadow for grazing. A headgate and small pond were constructed within the Angora Creek meadow to allow for irrigation later in the year. 

 

Irrigation was also applied to the meadow on the south side of the river within the area currently occupied by the golf course.  Ditches are extensive on the 1940 photos.  The diversion point on the river for this ditch system was upstream of the project area. This reach of Angora Creek was previously restored by state parks.

Development

Modern development led to further modification of the lower river.  The Tahoe Keys development in the early 1960s occupied a substantial portion of the delta and marsh at the lower end of the system.  The river was channelized along the margin of the development.  

Highway 50 bridges at South Upper Truckee Road and at the Elks Club Drive substantially altered the channel and floodplain.  Floodplain area was significantly reduced, and the channel cross section was narrowed.

The Lake Tahoe airport was constructed in the lower meadow reach in the early 1960s.  Almost entirely within the valley flat, the airport occupies most of this portion of this meadow.  The river was channelized along the eastern portion of the meadow, including substantial grade modification to control incision.

The Lake Tahoe golf course was constructed within the river floodplain between 1959 and 1964.  Several of the holes occupy former meadows and floodplain directly adjacent to the channel.  

In the lower portion of the project area, the golf course essentially borders the river, with only a narrow band of riparian vegetation remaining.  Five bridges have been constructed across the river within the golf course.  Because the bridges were generally undersized, most have required extensive maintenance to control local erosion.

Urban related development accelerated in the 1960s with a myriad of housing and roads throughout the watershed. Sewerlines were installed along river valley and floodplains. 

 

The sawmill reach of Angora creek was captured by the sewer excavation and the stream incised a new channel directly over the sewerline.  This reach was also restored by state parks. These changes may have increased peak flood magnitude and the delivery of fine sediment to the river.

GEOMORPHIC EFFECTS

River Channel Alterations

 

Because many of the impacts of European land use practices took place prior to photos or other records of the condition of the channel, the effects must be inferred rather than directly measured. 

The land use history has resulted in a substantially altered channel.  Channel length and sinuosity (curviness) have been reduced throughout the lower river.  In the project area, there has been a 28 percent reduction in channel length between 1940 and 2004.  In the 1940s aerial photograph, several meanders appear to have been directly cutoff.  Similar impacts occurred in broad meadows downstream to the lake. 

Straightening stream courses tends to accelerate water flows and cause bank erosion, which increases transport of fine sediments into Lake Tahoe . The mechanical process of straightening streams often results in the loss of wetland areas, which have the capacity to filter pollutants from the watershed.

In many locations, the channel has also been enlarged.  Channelization was designed to drain surrounding valley flats and provide flood protection, and the new channels that were constructed were therefore likely bigger and deeper to provide more hydraulic capacity. 

RIPARIAN ECOSYSTEM IMPACTS

Riparian Vegetation Impacts

Direct disturbance has altered many of the riparian vegetation communities in the lower river. 

Grazing in larger riparian meadows altered historic riparian vegetation, and changes in geomorphic processes resulting from channelization have impacted remaining riparian vegetation communities. 

 

Incision throughout the lower river has resulted in lowered groundwater tables in meadows.  Although the magnitude of incision has been relatively small (probably from two to five feet in most areas), the ecological consequences of lowered groundwater levels have been more substantial. 

In wet or mesic meadow communities, the majority of the root zone is within about two to three feet below the ground.  Changes of only one or two feet in groundwater level are sufficient to change wet communities to mesic types.  Lower groundwater tables have also shortened the growing season and generally reduced riparian plant productivity. 

 

Reduced sediment deposition from overbank flooding may also have reduced productivity as fewer nutrients are available for plant growth.

Although natural rates of streambank erosion promote shrub recruitment and vegetation community patchiness, incision has greatly increased the erosive stress and scour placed on streambanks during floods.  Streambanks are also higher, with less available moisture. 

As a result, riparian shrubs are less capable of colonizing streambanks disturbed during floods, and streambank instability is common throughout the lower river.  Riparian bands along the channel, particularly throughout broad meadows, have been eliminated or reduced in size.  

Streambanks and Erosion

 

Incised channels are more capable of transporting bedload and tend to export bedload, rather than storing it in bars within the channel.  Processes of channel migration have also been slowed by incision and, in many locations along the river, meander migration has been eliminated through rip-rap or other channel constraints. 

 

All of these changes have reduced the development of instream bars, particularly point bars, which are focal points for riparian shrub recruitment.  A loss of in-channel bars has reduced the area of riparian shrubs.  This impact is prevalent throughout broader meadows, but far less pronounced in reaches entrenched in outwash, where fluvial adjustment to incision has led to the development of extensive in-channel bars, and distribution of shrubs is widespread.  

In summary, human modifications of the floodplain and stream channel and subsequent channel responses have had important consequences for riparian vegetation communities.  Specific effects on riparian vegetation include the following:

Reduced frequency and extent of establishment of new individuals of the dominant, community-defining species;

Lower vigor (or death) and productivity of surviving individuals, especially of species that are not as tenaciously drought-adapted as C. nebrascensis or J.  balticus;

Overall conversion of wetter habitats to drier ones, and loss of small areas of standing water that are of great wildlife habitat value;

Reduced woody riparian habitat connectivity;

Lowered overall habitat complexity due to the ultimate loss of individuals from previous establishment episodes and lack of new colonization, resulting in lowered habitat values for wildlife;

And consequent loss of diversity and lowered resistance to future catastrophe, disturbance and/or gradual environmental change.

Aquatic Habitat

Historically, the river was the most important fishing resource for the Washoe tribe. 

The Washoe fishery focused on spawning fish from Lake Tahoe , especially Lahontan cutthroat trout and whitefish. 

 

Based on accounts from Washoe elders, Lahontan cutthroat spawning was most extensive in the middle reaches of the lower river, from about the upstream end of the project area to Meyers. 

Maps of preferred Washoe fishing spots focus on this area, where the gravel deposits preferred by salmonids for spawning were likely extensive.  Gravel recruited locally from outwash deposits and sorted and stored by channel processes including interaction with woody debris likely provided complex and high quality aquatic habitat.

These accounts suggest that the historic habitat throughout the lower river was comprised of abundant pools and gravel riffles.  Intact riparian vegetation likely provided extensive cover and allowed for undercut streambanks. 

 

Temporary development of a lagoon at the mouth of the river and a complex system of distributary channels immediately upstream were important rearing habitat for juvenile fish migrating back to Lake Tahoe. 

Channelization and resulting incision have dramatically altered aquatic habitat.  The direct result of channelization is simplified habitat, with the loss of pools and riffles.  Riparian cover was eliminated during channelization, and the high streambanks resulting from subsequent incision do not allow for the development of overhanging cover or undercut streambanks.  

Loss of Instream Cover, Deep Pools

 

It is also likely that woody debris is less abundant throughout the system, especially in reaches entrenched in outwash where lodgepole forests border the channel.  Reduction of woody debris has had important consequences for aquatic habitat. 

 

Perhaps the single best descriptor of functional aquatic habitat is high complexity; reduction of woody debris significantly reduces complexity.  This has led to less instream cover, fewer and shallower pools, less storage of gravel substrates important for salmonid spawning or macroinvertebrate habitat, fewer backwater and marginal habitats and reduced refugia during floods.

Subsequent changes in geomorphic processes due to the incision response have further exacerbated habitat degradation.  Much of the channel margin, particularly in low gradient meadows, consists of resistant  lacustrine deposits.  Gravel bedload is effectively transported over this material rather than being stored within the channel as bedforms. 

 

Gravel riffles, the required substrate for salmonid spawning, are now relatively rare, especially in meadow reaches, to the extent that the California Department of Fish and Game undertook a limited project to improve spawning habitat upstream of the project area, probably in the 1960s.