Statement_of_Work_1.pdf

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Statement of Work Snow Surveys for the Sprague River Basin, Oregon

1.0 INTRODUCTION AND BACKGROUND

The upper Klamath basin in southern Oregon has been subjected to extensive drought over the five years, and water resources have been overallocated for agricultural and ecological uses for many decades, causing competing demands for water as water supply has steadily decreased. Resource managers rely on surface water estimates from the National Resource Conservation Service (NRCS) and the National Oceanic and Atmospheric Administration (NOAA) to plan water allocations, and recent estimates have come with uncertainties that have caused reductions in minimum flows and lake elevations required for ESA-listed species, and curtailment of irrigation deliveries mid-season. To better understand the uncertainties in runoff estimates, USGS is proposing an effort to collect spatial snow depth, albedo, and snow-water equivalent (SWE) estimates in a sub-basin of the Sprague River Basin (SRB) and compare them to NRCS and NOAA estimates to improve understanding of snowpack-runoff relationships in this basin.

The Sprague River Basin (SRB) is a semi-arid sub-basin in the larger Upper Klamath Basin (UKB). In total, the basin drains an area of approximately 4,000 km2 east of Upper Klamath Lake (UKL). Precipitation in the SRB falls as snow in the valleys and uplands of the SRB, constituting 80% of the total precipitation in the basin. Streamflow in the Sprague River is greatest between December and June, representing seasonality in precipitation and snowmelt, and peak snowpack typically occurs between March and April. Snowmelt peaks can be small but of long duration between March and June. The SRB, combined with the neighboring Williamson River Basin, contributes approximately 50% of the streamflow to UKL annually.

UKL water is managed by the Bureau of Reclamation (BOR), which often results in conflict in dry years when there isn’t enough water to meet the basin’s ecological and agricultural demands. Understanding streamflow in the Sprague River is therefore important in the overall understanding of water availability in the UKB.

Snow conditions in the UKB are monitored by a network of NRCS SNOTEL stations, and BOR uses inflow forecasts provided by NRCS and NOAA based on the SNOTEL stations to plan for water allocations each water year. In recent years, inflow forecasts have been overestimated, which has led to challenges in managing water in the basin. In 2023, BOR requested technical assistance from USGS to better understand snowpack in the UKB and specifically called out airborne snow observation data collection as a priority to inform their surface water modeling efforts and to potentially be used to forecast snowpack runoff in upcoming years. As a result, two airborne flights were conducted in water year 2023, one snow-off flight and one snow-on flight which occurred during the melt-out period. Additional snow observation flights are needed in water year 2024 to characterize the snow accumulation period in addition to temporal and spatial variability in snow accumulation and snowmelt.

2.0 SCOPE

The objective of this contract is to acquire spatial snow depth and snow albedo measurements and to provide accurate spatial estimates of SWE in the upper Sprague River Basin using an

P. 2 of 4 airborne snow observation platform. These surveys shall be acquired through remote sensing using a paired lidar and imaging spectrometer system, conducted at periodic or strategic intervals that capture the snow accumulation season and beginning of the spring melt dynamics in addition to snow-off conditions when the snowpack has been fully melted. Measurements must be robust because of steep terrain and forested areas and capture the full variability in snow depth, snow albedo, and SWE via complete coverage of the area of interest (AOI) documented in this statement of work (section 3.0). Data acquisition must be able to respond to changing weather, and data reporting must allow the U.S. Geological Survey (USGS) to provide information to research collaborators and the public in a timely fashion. The advances in runoff forecasting made possible by remotely sensed snow surveys create substantial benefits to water users in the basin including the BOR, NOAA, the California/Nevada River Forecast Center (CNRFC), NRCS, the States of Oregon and California, regional and local irrigation districts, and provide broad public benefits for water-supply forecasting.

3.0 APPLICABLE DOCUMENTS

Area of interest for snow survey (below picture)

4.0 TECHNICAL REQUIREMENTS

The contractor shall perform the following tasks:

4.1 Collect snow depth and snow albedo data and calculate SWE estimates for the area of interest AOI attached to this statement of work, encompassing 1,471 km2 within the SRB.

One survey shall be conducted between February 1, 2024, and June 30, 2024, to capture snow accumulation conditions, unless the period is otherwise extended by mutual agreement. The USGS will consult with the contractor and set a 15-day target window to accomplish a completed survey, based upon weather and hydrology, which may require multiple flights across multiple days. This window will be scheduled to start at least 72 hours into the future, and the window may be rescheduled or shifted by mutual agreement.

4.1.1 The minimum services required by the USGS include: (a) snow depth accuracy with 5-centimeter precision or better across extremely rugged mountains and underneath forest canopy at a raw (LIDAR) resolution of approximately l point per square meter resulting in measurement aggregated at a scale of 5 meters or better, (b) modeling of snow density with snow depth data assimilation to derive SWE volume, which requires substantial expertise in snow science, (c) ability to acquire snow surveys from February 1 through June 30 within 72 hour-notice (weather permitting) and within a pre-defined window not to exceed 15 days, and

(d) ability to fully process data at full resolution within 72 hours and produce a report on current snowpack state.

4.2 Within one month of the completion of the survey, provide an electronic report containing a retrospective quantification of snow depth, snow albedo, and SWE estimates for the time between the snow-on and snow-off surveys within the AOI.

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5.0 DELIVERABLES

The contractor shall submit the following reports in accordance with section 4.2 by December 31, 2024.

Snow Survey Report (Task 4.2) and associated data products shall include:

a. Brief narrative of survey acquisition and conditions

b. Snow depth by 1,000-foot elevation band (table: mean, std deviation or percentiles)

c. Snow water equivalent by 1,000-foot elevation band (table: mean, std deviation or percentiles, total volume)

d. Tabular data subdivided by Hydrologic Unit Code (HUC) 10 units (as applicable) and aggregated for the AOI in Section 3.0.

e. 50-meter resolution geoTIFF files (rasters) of snow depth, snow albedo, and snow water equivalent for the AOI.

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