The Chehalis Basin Partnership is developing a Watershed Management Plan under ESHB 2514 for Water Resource Inventory Areas (WRIA) 22 and 23, which includes the entire Chehalis River watershed and watersheds that drain directly to Grays Harbor. Part of the process of developing this Watershed Management Plan is identifying data gaps that are significant to the planning effort, and conducting technical studies to resolve these data gaps.
In conjunction with the Watershed Planning project, the Partnership has undertaken several technical studies to resolve data gaps. The first two studies were data compilation reports: the Level 1 Data Assessment and Detailed Summary of the Level I Assessment. These two documents compiled, summarized, and presented relevant geological, hydrological, hydrogeological, water quality and habitat data for the Chehalis planning area. The Partnership is currently undertaking an In-stream Flow study under which streamflow is being measured throughout the summer and fall of 2002 at sixteen locations throughout the watershed where Department of Ecology regulations have established regulatory minimum flows, but actual flows have never been monitored.
The project scope presented in this document is designed to address the most significant data gap identified in previous Chehalis Watershed studies: the magnitude and distribution of consumptive water use. Data compiled to date have indicated that water allocations within the Chehalis exceed the actual streamflow in the river annually between April and October. Since the river does not dry up each year during these months, it appears that the magnitude of actual consumption is less than the amount believed to be legally appropriated to consumptive uses.
Refining the Partnership's understanding of the magnitude of the legal appropriation and actual consumptive use, and the difference between the two, is critical in developing the Watershed Management Plan. Since the current state of knowledge suggests that the watershed is over-appropriated, it leaves little opportunity for developing new management strategies. This has been the situation with water appropriation in the Chehalis for the recent past.
The distribution of the appropriated and actual uses throughout the watershed is also important to understand. If a city is looking for a new water supply, its search pertains to a specific geographic area. Likewise, the Department of Ecology evaluates water supply requests on a site specific basis. For this reason, it is necessary to better understand the "drain" on the river system from consumptive uses for fairly small geographic regions. This evaluation must be done at the subbasin (or smaller) scale.
The Steering/Technical Committee of the Chehalis Basin Partnership has also recognized the need to retain sight of the minimum requirements for Watershed Management Plans when conducting the supporting technical studies. These requirements, plus a few additional objectives identified by the Partnership, are shown in Table 1. The items listed in Table I are not intended as a set of objectives for the study described in this document, but rather to provide context and focus for the analysis.
1. Estimate surface and groundwater present in the management area.
2. Estimate water in the management area represented by claims in the water rights claims registry, water use permits, certified rights, existing minimum in-stream flow rules, federally reserved rights, and any other rights to water.
3. Estimate actual surface and groundwater use in the management area.
4. Estimate future water needs in the management area.
5. Identify known groundwater and surface water interaction locations, where:
a. Aquifers recharge surface waters (rivers, lakes, wetlands), such as galleries and springs.
b. Surface waters (lakes and other areas) recharge aquifers.
6. Estimate surface and groundwater available for further appropriation, taking into account the minimum in-stream flows adopted, or to be adopted, by rule, and necessary flows for fish. Take into consideration data needs to estimate necessary flows for fish.
7. Address water rights issuance questions (fn-1):
c. Is water available?
d. Beneficial use?
e. Will this impact others?
f. Is it in the public interest?
8. Public education'
9. Develop standards of practice for the Chehalis Basin that can be used for making water rights decisions'.
10. Assess water available in order to allow for restoration of habitat and riparian vegetation .
fn1 - These items are not minimum requirements under the Watershed Planning Act, but have been identified as goals by the Steering/Technical Committee of the Chehalis Basin Partnership.
The study described in the scope of work is comprised of two major tasks: the first is a rough-cut basin-wide water balance; the second is a pilot water quantity evaluation for the group of Chehalis subbasins consisting of the Newaukum, South Fork Newaukum, North Fork Newaukum, Skookumchuck River, mainstem Chehalis River near Centralia/Chehalis, and Salzer Creek (Subbasins 5, 6, 7, 9, and 10). Each of these tasks in described in the sections below.
TASK 1 - BASIN WIDE WATER BALANCE
Task I is the development of a generalized basin-wide water balance for the Chehalis watershed. This basin-wide water balance will be general in nature, and its purpose will be largely educational. It will help people understand the relative magnitude of the hydrologic "pieces" within the Chehalis watershed.
The basin-wide water balance will be based on the fundamental water balance equation:
Precipitation = Evapotranspiration + Runoff + Change in Groundwater Storage
The magnitude of each component of this equation will be resolved for the entire Chehalis watershed, (not including the tributaries that drain directly to Grays Harbor) based on published data, mostly from the Chehalis WRIA Level I Assessment.
A simple water balance diagram and estimates of basin wide quantities will be developed to show the relationships between the various components of the water cycle. Total precipitation must balance with surface water runoff, interception, surface storage, groundwater storage, water consumption, water recycling, and evapotranspiration. Estimates of quantities will be developed with the available information, and data gaps will be identified for further study. Data gaps previously identified include estimates of groundwater supplies, including shallow and deep aquifers, and actual usage by agriculture, commercial, and private consumers.
TASK 2 - WATER QUANTITY EVALUATION FOR PRIORITY I SUBBASIN GROUPING
Task 2 is a pilot Water Quantity Evaluation for a prioritized grouping of subbasins. This study will generate estimates of each of the water balance components for each subbasin within that grouping that are more refined in accuracy than the basin-wide water balance, and site specific to the subbasins studied. The reason for this type of study is to provide specific information needed to develop and make management decisions related to water quantity in the Chehalis River watershed.
The following approach will be used for the Water Quantity Evaluation:
Subtask 2.1 Prioritize subbasin groupings (completed). The STC conducted a priority ranking of all 30 subbasins in the Chehalis WRIAs based on identified risk to fish, magnitude of water appropriation, land use, and growth pressure. Based on the results of this ranking, three subbasin groupings were identified for pilot studies:
1. Newaukum and Skookumchuck Rivers, mainstem Chehalis River through the cities of Centralia/Chehalis, and Salzer Creek
2. Hoquiam and Wishkah watersheds
3. Black River, middle Chehalis River mainstem, and Cedar Creek.
The Partnership has initiated a pilot Water Quantity Evaluation study for the Priority I Subbasin Grouping consisting of the Newaukum and Skookumchuck Rivers, mainstem Chehalis River through the cities of Centralia and Chehalis, and Salzer Creek. This subbasin group was identified by the STC as the best candidate for the initial Water Quantity Evaluation. Once this pilot study is underway, the STC may initiate the second and third pilot studies if it appears that resources will be available.
Subtask 2.2. Delineate preliminary Zone of Significant Hydraulic Continuity. The hydraulic continuity zone is the region, surrounding a surface water body, where groundwater and surface water interact. It may be defined as the distance from a water body as established by groundwater travel time for a rainfall cycle. This distance allows groundwater withdrawal to occur outside of the buffer without affecting surface waters during low flow periods. The hydraulic continuity zone can be thought of as a buffer distance for groundwater and surface water planning.
The first step in delineating this zone will be to obtain and review available hydrogeologic data that may apply to this subbasin grouping. The preliminary delineation of the Zone of Significant Hydraulic Continuity will be based on available information concerning the hydrogeologic properties of the water table aquifer. This information is expected to be obtained from hydrogeologic studies, well logs, pump tests, and published estimates for aquifers of geologic composition. Given a likely range of hydraulic conductivity and hydraulic gradients, this zone will be determined to be the lateral extent to where a groundwater withdrawal would likely impact surface water flows during the annual low flow period. Groundwater flow modeling will be limited to a conceptual level for this study.
The water use assessment (described in the following item) will address water rights and water use within the preliminary Zone of Significant Hydraulic Continuity.
Subtask 2.3 Develop Data Components for Water Quantity Evaluation. The framework for the Water Quantity Evaluation will be a water balance, with particular emphasis on refining the understanding of water allocation and water use that may impact the surface water flows during low flow periods of the year. This refinement will focus on the following data components:
Precipitation: Estimates for precipitation will be obtained primarily from the Level I Assessment. We expect this data to come from available measured stations along with regional interpolations done for the Level 1 Assessment.
Streamflow data: Streamflow data, which will be the primary measure of the "Runoff' element of the water balance equation, will be obtained from measured streamflows and regional unit runoff estimates done for the Level I Assessment.
Evapotranspiration: Evapotranspiration estimates will be developed based on land cover and published estimates (primarily NRCS estimates) for different land cover types.
Change in Groundwater Storage: To estimate this component of the water balance, we will utilize available seasonal groundwater level measurements for wells that draw from the water table aquifer, to assess the seasonal fluctuation in water table elevation. This information will be used to estimate the change in groundwater storage throughout the year.
Water Allocation: The following three types of water allocations will be considered:
Permits and Certificates (water rights): The 49 largest rights will be individually assessed to determine the likelihood of them actively being used. This assessment is intended to screen out data entry errors in the Ecology data base that may misrepresent rights as much larger than they actually are, supplemental rights that may not be used regularly, and non consumptive rights (such as storage and fish propagation).
For all rights, location coordinates for GIS at the quarter-quarter section resolution will be developed for permits and certificates. Other important attributes of existing water rights will be catalogued, such as priority date, purpose of use, and instantaneous and annual rate and volume limits. This information will be built into a database for compilation, analysis, and manipulation during this and future work.
Water Right Applications (indicates future water demand): Water right application data will be compiled to assess the "official" pressure on future additional water consumption. Location coordinates for GIS at the quarter-quarter section resolution will be developed for water right applications.
Water Right Claims: The magnitude of possible consumptive water use from water right claims must be assessed. This assessment will be based on previously developed Ecology methodology for estimating water allocation (instantaneous and annual quantities) for water right claims when specific information is not available on the claims themselves. Claims will be located as precisely as possible within each subbasin. Since many claims do not contain specific location information, it is likely that many claims will need to simply be assigned to a subbasin with no further refinement of location at this point in time.
Water Use Estimates: The amount of water that is actually used for consumptive purposes may be quite different than the amount that is allocated. Our approach to developing more accurate estimates of actual water use will be the following:
Investigate Largest 49 Rights Individually . In each subbasin, there is a collection of water rights that are much larger in allocated quantity than the bulk of water rights. For example, in the Priority I Subbasin Grouping, there are a total of 6 1 0 water rights (not including claims). Of these 61 0 rights, the top 49 rights represent 73% of the allocated water (instantaneous allocation). This leaves 561 rights that make up the remaining 27% of the allocated water. We will investigate each of the 49 rights individually (as well as any exceptionally large water right claims), to learn more about the actual consumptive water use and timing of this use. A number of these 49 rights are for noncomsumptive uses, but they may impact flows in the Chehalis River and the water balance for each subbasin through changing the timing of that water being in the river, or by moving the water from one area of the subbasin to another.
Develop Water Use Estimates for Use Categories Because of the large number of water rights in the Chehalis Watershed (2495 water rights, 8,446 claims), it is not feasible to evaluate each one individually. As described in the paragraph above, we will individually investigate the exceptionally large water rights because these are few enough in number, and large enough in proportion of total water allocation to warrant that level of investigation. For the rest of the water rights (the most in terms of number of rights), we will develop consumptive use estimates based on categories of use. This is the most reasonable approach at this point in time because it will result in a substantial increase in our level of knowledge about consumptive water use in the watershed, and can be accomplished with a level-of-effort that is available to this project. The following categories of consumptive use have been identified; estimates will be developed for each category and its components:
Agriculture (irrigation, dairy, stockwater)
Municipal (includes some commercial/industrial)
Domestic (mostly water districts and private water systems)
Commercial
Power
Fish Propagation
Consumptive use estimates will be developed with aid from published resources such as NRCS crop use estimates and Washington Department of Health guidelines for estimating domestic needs. In addition, local factors, such as available information about the likely efficiency of water delivery systems, will be integrated into the estimates. The focus for these consumptive use estimates will be on better understanding bow much water is actually being used, not on how little water could be used to meet the current needs.
Develop Consumptive Use Estimates for Exempt Wells . Private wells that serve individual homes are located throughout the Priority 1 Subbasin Grouping, most likely in rural areas, and those areas not served by water systems. These wells do not require a water right, and therefore the State may have not have any documentation about their existence.
The Level 1 Assessment displayed two examples of methodologies for quantifying exempt wells. The first was a population-based method that relied on population data, public water system information, and the WRATS water right database; the second was a parcel-based (mapping) method. The parcel-based method requires detailed mapping of water rights to determine which parcels must be served by exempt wells.
The consumptive use estimates developed for the Priority I Subbasin Grouping will likely draw from both of these methods. Where detailed water right mapping is done, exempt well estimates will be based on a parcel-based method. For other areas these estimates will be based on the population-based method.
Estimates for Return Flows from Water Diversions/Withdrawals . When water is diverted for a consumptive use, there is often a portion of the diverted water that is returned to the watershed. For irrigation and septic systems, a portion of the water may be returned to groundwater. For municipal, irrigation, fish propagation, and hydropower uses, a portion of the diverted water is returned to the river (for municipal systems this discharge is through the wastewater treatment plan discharge). The Level I did not estimate the impact of these return flows.
Subtask 2.4 Documentation of Study Results
Documentation of study results will be comprised of the following:
An updated and expanded GIS project for the Priority I Subbasin Grouping. A major work component of this study will be acquiring and building data sets, expanding the Chehalis GIS project, GIS data analysis, quality control auditing of GIS data, and preparation of maps and figures for analysis and illustration of study findings.
Documentation describing the database that contains the information used for the evaluation, and
A narrative report summarizing major study findings. This report is anticipated to be focused on maps produced through the GIS and data analysis, with a short narrative describing salient findings for each subbasin.
TASK 3 - TRIANGLE ADMINISTRATION AND PROJECT MANAGEMENT
This task covers Triangle Associates administration efforts including contract administration, project oversight and management, quality assurance and quality control, project tracking, participation in project meetings, and preparation of monthly progress reports and invoices.
PRODUCTS
This study will result in the following products that will directly support the Chehalis Watershed
Management Plan:
A major product from the study will be an expanded GIS project for the Chehalis watershed. The GIS project will be updated and expanded to contain the information developed for the Priority I Subbasin Grouping.
A basinwide conceptual water balance, based on Level I Assessment data
Water Quantity Evaluation report and maps describing the results from the data developed for Task 2, described above.
The mapping and refined estimates will serve as the first step in quantifying water resources at the subbasin level. The water balance will be reviewed for component sensitivity, that is, relative effects of changes to well use, surface water use, wastewater return, crop land type, urban cover, domestic conversion from agriculture, etc.
Through this pilot study, the CBP will gain a better understanding of the magnitude of effort required to complete this sort of work for the entire watershed. Eventually, the Chehalis River Watershed Management Plan will prioritize all of the sub-basins and develop a plan for implementing and finding other subbasin evaluations that are not pilots, and using the pilots as models for how to accomplish this effort.
This study will lay the necessary groundwork for developing recommendations to address water management in the Chehalis. Through this work it will become possible to identify opportunities for better management, and to assess the impacts and benefits of possible options such as:
Siting of new wells outside of the continuity zone
Conversion of water supply from surface water to well
Establishment of zone vulnerability criteria
Identification of vulnerable zones
Land use management for site water intensive uses in vulnerable zones
Local water balance evaluation for compensatory storage, recycling, or groundwater injection
This page created and maintained by Chehalis River Council
Send comments or questions to the: Chehalis River Council