~ Hydrology and Water Quality ~

3.2.2-1 SETTING
This section describes the local and regional hydrologic conditions in the Brooktrails Township area, and evaluates the way in which the proposed Specific Plan could affect surface water hydrology and water quality, erosion and sediment transport, and groundwater resources.

Regional Hydrologic Setting
Brooktrails Township is near the upper end of the Eel River watershed. The Eel River drains an area of approximately 3,684 square miles in the Coast Ranges, emptying into the Pacific Ocean about 15 miles south of Eureka. The watershed is about 120 miles long, averages 30 miles in width, and trends northwest, almost parallel to the Mendocino Coast. Elevations in the generally rugged terrain range to over 7,500 feet above mean sea level. Figure 3.2.2-1 is a map of the Eel River watershed.

The climate of the Eel River watershed is one of the wettest in California, with annual average precipitation ranging from 35 inches along the coast to more than 110 inches in the mountainous areas. The average for the watershed is about 59 inches. Most of the precipitation falls in the form of rain during large storms that move into the area from the northwest in the late autumn and winter months. Snow falls at the higher elevations, but its quantity and contribution to runoff usually are inconsequential. Although the watershed covers only about 2 percent of the land area of California, its average annual runoff constitutes about 9 percent of the runoff from the State.

Figure 3.2.1-1: Eel River Watershed
The average annual runoff from the Eel River watershed is about 6.8 million acre-feet (AF). Precipitation and runoff follow a seasonal pattern, with the majority of the precipitation and runoff occurring between November and March. Because of the lack of snow and storage, streamflow is highly responsive to precipitation, and high flows diminish quickly in the absence of sustaining rainfall.

The Eel River has the highest recorded average annual suspended sediment yield per square mile of drainage area of any river of its size or larger in the United States. The combination of geology, soil types, steep slopes and heavy precipitation produces slumps and landslides that contribute heavily to the sediment yield of the watershed. In places where the landslides are adjacent to stream channels, sediment production is consistently higher than in other areas. Landslides occur most frequently in the Middle Fork Eel River basin and along the slopes of the main reach of the Eel River in the central part of the watershed. Erosion may become severe in other areas that have been subjected to heavy grazing or to deforestation by fires or lumbering practices.

The major surface water features in the watershed are Lake Pillsbury (storage capacity 93,700 AF) impounded behind Scott Dam near the upper end of the watershed, and Van Arsdale Reservoir, located just downstream of Lake Pillsbury. An average of about 147,000 AF per year (one-third of the Eel River flow at this point) is diverted to the Russian River basin at Van Arsdale Reservoir, through the Potter Valley Tunnel and Powerhouse. However, these structures involve only about 10 percent of the total drainage area of the Eel River and, therefore, have little effect on the natural runoff pattern in the lower Eel River.

Locally, Morris Reservoir, on Davis Creek, has a storage capacity of about 600 AF and has provided water supply for the Town of Willits for a number of years; recently, Willits constructed a new 700 AF reservoir upstream of Morris reservoir. Two reservoirs in the Willits Creek watershed provide 265 AF and 135 AF for the municipal water supply to Brooktrails Township.

Regional Water Quality
A water quality investigation was conducted for the Eel River basin in the 1970s. The study conducted water quality sampling for more than three years, and analyzed water quality data that have been collected since the 1950s. It was determined that the water quality of Eel River watershed generally is quite good. The concentrations of major inorganic chemical constituents (calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride and nitrate) were correlated to discharge rates; that is, the concentrations of these constituents tended to increase with higher flow rates. Concentrations of ammonia nitrogen, organic nitrogen, nitrate, phosphorus and total organic carbon tended to increase with increasing distance downstream. Concentrations of trace elements were low, generally at or below the limits of detection. Pesticides were not detected in any water or sediment samples.

Brooktrails Township Hydrology
There are actually several small watersheds in Brooktrails Township, all of which are tributary to Outlet Creek, a major tributary to the main reach of the Eel River above its confluence with Middle Fork Eel River. Willits Creek watershed is, by far, the largest at approximately 5.55 square miles, draining to Mill Creek, which flows through the Town of Willits to Outlet Creek in Little Lake Valley. The other watersheds are Upp, Bull and Rowes creeks, all of which, together, drain less than one square mile of Brooktrails, along the northeast boundary of the Township directly to Outlet Creek. Other local tributaries to Outlet Creek include Baechtel, Broaddus, Davis and Haehl creeks. The majority of the Outlet Creek watershed is characterized by lower elevations, more gentle slopes and generally less erodible materials than those in the Willits Creek watershed.

The Willits Creek watershed contains two prominent creeks: Willits Creek and its main tributary, Dutch Henry Creek which joins Willits Creek at Lake Emily. Several small tributaries flow into Willits Creek. One unnamed creek flowing through the old Brooktrails Ranch headquarters joins Willits Creek at Lake Ada Rose. The average annual precipitation over these watersheds is about 52 inches, with an average annual runoff estimated at about 86 percent, yielding about 8,500 AF. The remainder of the precipitation is lost to direct evaporation or is taken up by vegetation.

Two domestic water-supply reservoirs in the Willits Creek watershed provide municipal water supply to Brooktrails. Lake Emily at the confluence of Willits and Dutch Henry creeks has a capacity of about 265 AF (including 75 AF of storage provided by flashboards) and drains an area of about 4.91 square miles. Lake Ada Rose at the confluence of an unnamed tributary and Willits Creek has a drainage area of about 0.64 square miles, and has a storage capacity of 135 AF. The total existing storage capacity for the Township is about 400 AF.

A water quality analysis of the raw water used by Brooktrails determined that the water is generally of high quality, and that following the treatment provided by the Township, adequately protects public health and is suitable for domestic use. The raw water is low in total dissolved solids, relatively low in alkalinity, has a low pH, and is soft. The raw water does exceed the recommended limit for manganese and iron (corrected during treatment), and at certain times of the year has odor and color resulting from the high levels of turbidity.

Turbidity is normally low, except during high runoff periods, and filtration as well as settlement is used to correct this effect.

Drainage and Flooding
The Federal Emergency Management Agency has zoned Mill Creek, downstream from its confluence with Willits Creek, with respect to its flooding potential. The 100-year flood is contained within a well-defined channel upstream from Highway 101 (Main Street), with expected flood depths between 3 and 5 feet. A wide area of shallow flooding (less than 1 foot) and a narrow zone of 100-year flooding (up to 3_ feet) between Main Street and the old Southern Pacific tracks are confined by the highway and railroad embankments. East of the old SP right-of-way Mill Creek enters the 100-year floodplain of Little Lake Valley where broad areas of shallow flooding (up to 1 foot) occur during major storms, at least once a year. The City of Willits maintains three 12 X 8 foot culverts under Mill Creek Drive which pass the 100-year storm event in Mill Creek with sufficient freeboard to accommodate much larger storms by metering the flow downstream through the City. In the recent very heavy storm event of 1992/93 tree trunks had to be removed from one of the culverts to restore free flowing conditions, but sufficient freeboard remained to prevent flooding of Mill Creek Drive, 8 feet above the culverts, and to prevent flooding downstream. Although the Mill Creek drainage system capacity is adequate for the foreseeable future, Outlet Creek, into which Mill Creek flows, experiences shallow floods during every major storm event. The culverts under Highway 101, three miles north of Willits, act as meters for Outlet Creek to the north and back up water into Little Lake Valley to the south.

Because of the preponderance of steep slopes and thin soils in Brooktrails Township, the runoff factor is high, even in undeveloped areas. In flatland areas or areas with gentle slopes, typical runoff factors for woodlands range from 5 to 25 percent of rainfall. For barren slopes steeper than about 30 percent, the runoff factor is between 70 percent and 90 percent of rainfall; about the same as for a heavy industrial area or a paved road. As previously stated, it is estimated that 86 percent of rainfall in Brooktrails becomes runoff, despite the extensive forest cover. This is explained by the soil and rock conditions in the Township. The soils are fairly thin (that is to say, the underlying bedrock is close beneath the ground surface) and loamy (about 30 percent clay) so they become saturated rapidly. Additional rain simply flows over the surface of the saturated soil without sinking in. The rocky slopes are quite steep (in many areas steeper than 40 percent) so rainfall does not remain on a given hillside long enough to soak in, unless the storm is prolonged. Even then, rainfall often penetrates the thin soil only to flow down the bedrock surface to a nearby seep at a lower elevation and re-appear as runoff. Consequently, the existing developed areas in the Township, even if they were as impermeable as paved roads, would be only slightly more impermeable than the average for the entire watershed, and they represent less than 9 percent of the land surface. Even if the developed area were double to nearly 18 percent of the land area, the average runoff for the Township would increase by less than _ of 1 percent, still within the capacity of the existing drainage system, and not enough to be considered a significant impact on potential downstream flooding.

Sediment Transport
Every stream transports sediments that have eroded from the watershed. Sediment transport consists of bedload and suspended load. Bedload refers to that portion of the total sediment load that moves along the bottom by rolling or sliding, and generally is composed of sand and coarser particles, greater than 1.0 mm in diameter. Suspended load refers to that portion of the total sediment load carried in suspension by the flowing water, generally particles smaller than 0.5 mm. Erosion rates within the watershed vary from storm to storm, depending on rainfall intensity and soil particle size. Sediment eroded from the watershed during one storm may be deposited in the stream channel, but remain there until a subsequent storm washes it downstream.

Sediment transport rates are strongly correlated with river flow rates: the higher the stream flow, the higher the rate of sediment transport. This is because the energy necessary to move the sediment load is provided by the flowing water. Higher flow rates provide more energy with which to move the sediment load. Sediment transport fluctuates from near zero during low flow periods to extremely large quantities during major floods.

The total amount of sediment that passes any point of a stream is referred to as the sediment yield, often expressed in terms of tons per square mile of drainage area per year. While no specific data are available, the sediment yield of Willits Creek is estimated to be on the order of 1,000 tons per square mile per year. This estimate is based on both general hydrologic information and specific studies done on the Eel River basin. Erosion rates along Willits Creek are considerably below average for the Eel River basin as a whole, which generally has a quite high sediment yield.

Groundwater
A study of the groundwater resources of Mendocino County indicates that most of the County, including Brooktrails Township, is underlain by consolidated rocks of the Franciscan assemblage: rocks usually are dry and generally provide well-yields of less than 5 gallons per minute (gpm). Little Lake Valley, east of the Town of Willits, contains unconsolidated soil materials consisting of gravel, sand, silt and clay, and is the area nearest to Brooktrails that has important groundwater resources. Well-yields in the valley range from less than 50 gpm to over 1,000 gpm, depending on the porosity and permeability of the unconsolidated fill. The main source of groundwater recharge for Little Lake Valley is precipitation as rainfall. Generally, precipitation of 60 to 75 percent of normal fills these groundwater basins to capacity, and no long-term overdraft is occurring. The groundwater level is less than 15 feet below the valley floor; however, high salinities and small pockets of gas prevail at depth, making extraction of water from deeper areas infeasible.

Regulatory Setting
Protection of water quality within California is the responsibility of the State Water Resources Control Board. The State Board acts jointly with the nine Regional Water Quality Control Boards (RWQCBs) to provide State-level coordination and regional familiarity with local needs and conditions. The North Coast RWQCB has regulatory authority over the waters in the Brooktrails area. A general permit for Storm Water Discharges Associated with construction Activities is required for any construction project disturbing more than five acres from the State Water Resources Control Board. The permit requires the development of a plan to prevent deleterious erosion and sedimentation impacts.

Comprehensive water quality planning is set forth in the Water Quality Control Plan or "Basin Plan" for the North Coast Region. The basin plan lists a total of 14 beneficial uses of the Eel River that must be protected against water quality degradation. These beneficial uses include municipal and domestic supply, agricultural supply, industrial service supply, groundwater recharge, navigation, hydropower generation, water contact recreation, non-contact water recreation, warm freshwater habitat, cold freshwater habitat, wildlife habitat, preservation of rare and endangered species, fish migration and fish spawning.
The State Water Resources Control Board, Division of Water Rights, is a quasi-judicial body that administers water rights within California. The Township must obtain a Permit to Appropriate Water in order to allow the diversion of water from Willits Creek. The SWRCB establishes the right of the applicant to use water, and the priority of that right. In addition, the SWRCB is concerned that permittees prevent waste, practice water conservation, and use the water to the fullest beneficial use.

3.2.2-2 IMPACTS AND MITIGATION MEASURES

Brooktrails Township Specific Plan Policies. Plan policies specifically related to protection of the Township's water supply appear in the Environmental Resources chapter of the Plan as HYDROLOGY AND WATER QUALITY GOAL ER-6.4. The Policies for implementing this Goal are so central to the control of turbidity in the Plan area that they are reiterated here to allow the reader easy reference to the actual language in the Plan.

HYDROLOGY AND WATER QUALITY GOAL ER-6.4:
Ensure existing and future development does not degrade Township water quality or cause sedimentation of Township waterways and reservoirs.

POLICY ER-6.4A: Protect the Township's water supply by controlling future construction around lakes, creeks and other water supply sources.

POLICY ER-6.4B: Protect the Willits Creek watershed from erosion and sedimentation. Stabilize stream banks with vegetation and other low impact restoration techniques as necessary.

Standards of Significance
The CEQA Guidelines indicate that a project normally will have a significant adverse impacts to water quality or hydrology if it will cause 1) substantial flooding, 2) substantial degradation of water quality (including siltation from erosion), or 3) substantial interference with groundwater recharge. For the purpose of this document, the potential hydrologic effects of the Brooktrails Township Specific Plan are considered from two points of view: the short-term effects of construction and the long-term effects of operation. Based on these criteria, implementation of the Specific Plan would not have significant adverse impacts on hydrology and water quality, either short term and long term, because the Specific Plan contains mitigation measures in the form of water quality protection policies.

Impact 3.2.2-1
Grading and excavation on, or adjacent to, existing steep slopes, whether underlain by bedrock or alluvial deposits, could create or exacerbate erosion conditions at the construction site, and to cause subsequent deposition of particles in drainage ways, creeks, or reservoirs. (PS)