# Presentation: 132821

## Walker River Basin Project

**Science to Sustain At-Risk Terminal Lakes**
**Walker River Basin**** Project**

**In Cooperation with the Bureau of Reclamation**
**Legislative Committee on Public Lands**
**March 24, 2006**

**Notes:**
Ongoing study that began in 2004.
Being done in cooperation with BOR.

## Presentation Overview

- Problem
- Objectives
- Status of activities
- Plans for upcoming year

## Location of Walker River Basin

**West Walker R. near Hudson**

**East Walker R. above Strosnider Ditch near Mason**

**Walker R. at Lateral 2-A near Schurz**

**Notes:**
Walker River Basin, about 4,000 square miles, straddles CA-NV border.
Most precipitation is snow in Sierra
Snowmelt flows down the east and west forks, which merge in Mason Valley and flows to Walker Lake.
Three reservoirs store water for irrigation: Bridgeport, Topaz, and Weber.
Most agriculture is in Mason Valley.

## Walker Lake Salinity

**Notes:**
Perennial, natural terminal lake that has become at-risk from increasing salinity.
As lake declines, salinity increases.
Declined about 150 feet since 1880, TDS increased from 2,500 mg/L to 16,000 mg/L.
The Lahontan cutthroat trout, a threatened species native to Walker Lake, has adapted to high TDS, but TDS is near levels that threaten survival.
During droughts of about the past 20 years, little streamflow has reached the lake and caused the lake to decline at a constant rate.
Similar rates of decline during past droughts, but not as steep.

## Walker River Streamflow

**Notes:**
Decline in lake level mostly due to diversions for agriculture.
Most water is lost in Mason Valley (difference between black and red bars), which has the most agriculture.
Relatively little water lost downstream from Wabuska.

## Objectives

- Quantify streamflow in the Walker Basin
- Estimate evapotranspiration from the lake and vegetation
- Develop an improved water budget for Walker Lake
- Develop the capability to predict how changes in upstream irrigation practices would affect flows to Walker Lake

**Notes:**
Project focused on reach downstream from Wabuska to Walker Lake.
The amount of water lost in this reach is unknown.
Uncertainty due to unknown gw/sw interactions (gaining/losing reaches), possible gw outflow to Rawhide Flats, and gw discharge to lake.

## Activities

- Surface-Water (SW) network
- Ground-Water (GW) network
- Evapotranspiration (ET) network
- Mapping vegetation, elevation, bathymetry
- Preliminary streamflow analysis
- Web Site

## SW Network –new and upgraded gages

**Notes:**
14 continuous gages in basin prior to project, currently 19, plan to add 2 more.
Upgraded many stations to real time, including lake gage.
Installed new stations, continuous and crest-stage gages (CSGs).
Installed 2 precipitation gages, Wassuck and Gillis Ranges (not on map)
Waiting on construction for Topaz Diversion and W. Walker at Diversion gages

## New Stream Gages

- Green Ck near Bridgeport              Virginia Ck near Bridgeport

## Real-Time Data on Walker Lake Gage

**Notes:**
Provisional data, may see spurious blips which will be edited.
In 2005, there was a 2-foot rise in lake level from snowmelt runoff.
First substantial rise since 1999.
However, by Oct/Nov lake level was down to pre-runoff levels due to evaporation.

## GW Network

- GW sites

**Notes:**
Water levels measured in about 200 wells each year.
Wells measured spring/fall before/after irrigation season.
Subset of wells measured monthly.
One well at well nests installed for project have transducers for continuous data.

## Ground-Water/Surface-Water Sites

- Willows ET (above Weber)
- Cow Camp Gage
- Lateral 2-A Gage
- Powerline Road
- Walker River at Mouth

**Notes:**
Each gw/sw site consists of well nest with 3 wells to define water table near river.
Co-located at sw gages, between gages, and river mouth.

## GW/SW Site Locations

**Notes:**
Location of gw/sw sites.

## ET Network

**Notes:**
Eight ET stations, five Bowen and three Eddy correlation.
Lake, alfalfa, and phyreatophytic vegetation.
Also using data from a RAWS weather station.

## Results – ET from Walker Lake

- Results – ET from Walker Lake

## Measured ET on Walker Lake

**Provisional-****—****Subject to revision**

**Notes:**
Plot shows good correlation between net radiation and ET.
ET most due to net radiation, but no data during missing periods.

## ET compared with RAWS Radiation

**Provisional-****—****Subject to revision**

**Notes:**
Plot shows correlation between ET and solar radiation from RAWS site.
Still good correlation, even though not net radiation.
RAWS data exists for missing periods, can be used to estimate ET.

## ET vs RAWS radiation

**Provisional****—****Subject to revision**

**Notes:**
RAWS radiation vs ET for periods when equipment worked.
Equation fit to the data, was used to estimate ET for missing record.

## Total ET for 2005 Water Year

**Total 2005 Water Year ET = 1814 mm or 6.0 ft***

**Provisional****—****Subject to revision**

**Notes:**
ET for WY05 with estimated ET.
Total ET 6 ft.

## Results – ET from Walker Lake

- ET for WY2005 was 6.0 ft*, up from previous estimates of 4.1 ft.
- Area of Walker Lake in June 2005 was 32,000 acres.
- Volume evaporated from Walker Lake in 2005 was 192,000 acre-ft*.
- ~ 50% increase over previous estimates.
- If relation between Lake ET and RAWS solar radiation holds, may be able to estimate annual ET from 1999-2004.

*** Provisional****—****Subject to revision**

**Notes:**
1. Can get better idea of average annual ET from multiple estimates.

## Salt Cedar site

- Site underwent substantial defoliation due to introduction of a biologic control agent: Salt Cedar Leaf Beetle (*Diorhabda elongata*)
- Changed characteristics and ET rate for large stand of Salt Cedar

**Notes:**
Salt cedar is an invasive species that invades riparian areas and uses water.
USDA released salt cedar beetle into study area, effect show in photo.
Bush on left treated with pesticide, right and background untreated, defoliated due to beetle.
Reduced ET.

## Reduction of ET using Salt Grass

- 203 mm*

- 57 mm*

- This is a 22% reduction in ET*

**Provisional****—****Subject to revision**

**Notes:**
Area in black is the amount of ET reduction caused by beetle.
Reduced ET by about 22 percent.

## Results – ET Summary

- 6.0 ft

- 3.5 ft

- 3.3 ft

- 2.8 ft

- 0.7 ft

- 0.7 ft

- 0.4 ft

- 0.4 ft

**Provisional****—****Subject to revision**

## Mapping:

- Satellite imagery
- New imagery
- Lidar
- Bathymetry
- Side-scan sonar

- Bathymetry

**Notes:**
Landsat satellite imagery being used to map vegetation throughout basin.
 New imagery and Lidar flown last year. Data are being processed by LaRue. Photo shows Weber Reservoir, riparian area just upstream, and riparian area from Schurz to lake (Cottonwood and Salt Cedar). Also agriculture in Mason and Smith Valleys. 
New imagery used 4 color bands to distinguish vegetation types. 
Lidar is highly accurate (10 cm) elevation mapping. 
Lidar will be combined with bathymetry to better define relation of lake elevation/surface area/volume and to estimate ground-water altitude in very flat areas such as area near Adrian Valley.

## Imagery (infrared)

**Notes:**
Example of infrared imagery.
Red areas show where vegetation is, used for mapping.

## Scaling up of ET

- Create map of ET units
- Extrapolate ET data to ET units to estimate total ET in basin

**Notes:**
Example of vegetation map from southern NV project.
ET units are areas where ET rates are similar, based on plant type and density.

## Bathymetry

**Provisional****—****Subject to revision**

**Maximum depth Spring 2005 was 82.8 ft**

**Notes:**
Bathymetry: mapping lake bottom to estimate lake elevation-surface area-volume relation.
Single-beam sonar, almost 900,000 depth measurements along 250 miles of transects across the lake.
Surface area and lake ET used to estimate volume of water that evaporates.
Bathtub shape, mostly smooth bottom with steep sides on west, shallow slopes elsewhere.
Black area shows how much lake has declined since ortho-photo taken.
Deepest point was 82.8 ft.

## Slide 28

**Notes:**
Very similar to Rush’s bathymetry.
Explain how to use graph.
Area of lake accurate, but evaporation rate is much higher.
Volume evaporated much higher than previous estimates.

## Tufa Mounds in Walker Lake?

- Side-scan sonar
- More GW inflow?

**Notes:**
During bathymetry, found what appear to be tuffa mounds up to 7 meters tall. 
Most in south center of lake.
Would indicate more gw discharge to lake than previously estimated.
Used side-scan sonar and underwater camera to acquire images of mounds last September, but no clear evidence of mounds.
Also measured conductance, temperature around densest mounds, but water was well mixed, no indication of gw discharge.

## Effect of ET on Streamflow

**Notes:**
Difference in daily discharge between Wabuska and above Weber gages, never exceeded 200 ft3/s during this period.
Daily discharge offset by one day to account for travel time between gages. 
Smallest difference is between November to March (yellow shading), vegetation dormant 5 months, transpiring 7 months.

## Streamflow—Wabuska vs Schurz

**Notes:**
A gage existed at Schurz before Weber Dam construction began in 1933, Lateral-2A gage near Schurz installed in 1994.
No apparent difference in discharge at/near Schurz following construction of dam.
Indicates minimal change in water use/loss during past 90 years.

## Web Site

- _[http://](http://nevada.usgs.gov/walker/index.htm)__[nevada.usgs.gov](http://nevada.usgs.gov/walker/index.htm)__[/walker/](http://nevada.usgs.gov/walker/index.htm)_

**Notes:**
1. Project web site, info and data on project.

## Slide 33

## Slide 34

**Notes:**
Provisional streamflow data.
Unit value data from 1 to past 31 days can be plotted and downloaded.
Other links on water data pages to get mean daily values, other data.
Example is New Years Eve flood on Walker River at Wabuska.

## Plans for This Year

- Continue to collect data – Data network is essentially in full operation
- Report on bathymetry of Walker Lake
- Classify and map vegetation
- Geophysics near Double Springs, river mouth, and south end of lake
- Install additional observation wells to refine hydrologic understanding of GW system

## Slide 36

**Notes:**
1. Questions?