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CURRENT LOWER PUTAH CREEK FLOW

Hydrogeography of Putah Creek

The Putah Creek watershed lies on the eastern slope of the Coast Range, south of the Cache Creek drainage and north of Napa Valley. The drainage encompasses southern Lake County. the northern half of Napa County, and small portions of Yolo and Solano Counties. Putah Creek originates from the northwestern corner of the drainage, off Cobb Mountain in Lake County, and flows southeastward, into the Yolo Bypass near Davis. For management purposes, the Putah Creek watershed is typically divided into the "Upper Drainage", which encompasses the 576-square mile area upstream of Monticello Dam, and the "Lower Drainage", which consists of a considerably smaller but less precisely defined area between Monticello Dam and the Yolo Bypass. Approximately 90% of the total annual flow of Putah Creek measured at the confluence of Putah Creek and the Yolo Bypass, originates from the Upper Drainage.

Lower Putah Creek is defined as the 23-mile stream segment located between the Puath Diversion Dam and Putah Creek's confluence to the Yolo Bypass. Based upon hydrologic characteristsics Lower Putah Creek is sub-divided into five designated reaches:

1. Putah Diversion Dam to Interstate 505 Bridge - "PDD-505"
2. Interstate 505 Bridge to Stevenson Road Bridge - "505-STV"
3. Stevenson Bridge to Interstate 80 Bridge - "STV-I80"
4. Interstate 80 Bridge to Mace Boulevard - "I80-MCE"
5. Mace Boulevard to the eastern boundary of the Yolo Bypass, River Mile 0.0 - "MCE-RM0"

The PDD-505 reach, the shortest of the five reaches, can be charcterized as a broad alluvial channel in which stream flow percolation losses are typically the greatest of all the reaches. Downstream of Interstate 505 the stream channel narrows and becomes deeply incised. In the 505-STV reach, groundwater seeps into the channel and can augment surface stream flow. The STV-I80 reach is in close balance between stream flow gains and losses typically with a modest net toward loss. Similar conditions prevail downstream between Interstate 80 and River Mile 0.0. In general, all reaches EXCEPT for the 505-STV which is a "gaining" reach, are "losing" reaches whereas nearly half of the total net stream flow percolation losses occur in the PDD-505 reach, while the majority of all steam flow gains in the vicinity of Stevenson Bridge.

The Solano County Water Agency provides water to Lower Putah Creek for environmental protection and to meet valid water rights.  Water is released to Lower Putah Creek from Putah Diversion Dam to maintain a minimum flow at the Interstate 80 bridge and flow downstream to the western boundary of the Yolo Bypass based on this monthly schedule:  

Compliance is monitored by the Solano County Water Agency through implementation of the Lower Putah Creek Stream Flow Monitoring Program (Monitoring Program) - a field monitoring program involving a combination synoptic observations, stream flow measurements, and continuous permanent monitoring stations. Our continuous monitoring station network provides near "real-time" information on current stream flow at key location along Putah Creek. See the Current Hydrologic Condition of Lower Putah Creek from our existing network which is continually growing.

Lower Putah Creek Riparian Water

Riparian stream flows are defined as any surface water derived from precipitation or rising groundwater that, given prevailing hydrologic conditions, would occur in Lower Putah Creek in the absence of the Solano Project. Non-riparian water, such as treated wastewater and agricultural return flows originating from a non-riparian source (e.g., pumped groundwater that would not otherwise be tributary to the creek) cannot, by definition, be diverted by riparian water right claimants and, therefore, is not included as a source of riparian water from Lower Putah Creek. State law governs that the limited amount riparain water available is shared correlatively among all legitimate riparian users. Additionally, riparian water pumped from Lower Putah Creek can legally be applied only on those lands within the legal boundary of the riparian property establishing that right. No adjacent, non-riparian parcels may be irrigated with riparian water.

During certain times of the year - generally late suumer and fall - much if not all of the available stream flow in at least portions of Lower Putah Creek consists of stored water releases from Lake Berryessa. These stored releases are by definition not riparian water and therefore cannot be diverted under a riparian water right claim.Some of the stored water released is reserved specifically for the protection of the environment and cannot be diverted from Lower Putah Creek under any circumstances.

Each year the Solano County Water Agency provides "riparian water availibility forecasts" for Lower Putah Creek to all riparian landowners. The purpose of this forecast is to inform riparian water users along Lower Putah Creek - how much, and for how long, riparian water is anticipated to be present during the forthcoming months of April through October. This information is provided so that the riparian water users can consider the projected availability of riparain water before planting a given crop, and if necessary, begin making preparations to obtain alternative water to irrigate their crops in the event that the projected riparian water supply is inadequate to meet their water supply needs.

The Lower Putah Creek Riparain Forecasts are based on stream flow conditions observed in the Putah Creek drainage, upstream of the Putah Diversion Dam, in the prior (i.e., antecedent conditions) and current water year. Forecasts are made on January 1, March 1 and May 1. The January 1 and March 1 forecasts, which are made before the current rainy season is over, are based in part on projected stream flow conditions for the balance of the rainy season, while the May 1 forecast, the final forecast for the water year, is based on actual runoff measured to date. Both the January 1 and March 1 forecasts include three scenarios, based on the assumption that the balance of the rainy season will either be "wet" (25% exceedance), "normal" (50% exceedance) or "dry" (75% exceedance). In order to address the differing sources and durations of riparian stream flows (surface stream flows from Putah Creek and/or tributaries to Putah Creek, or rising groundwater), the forecast is differentiated between the five reaches. Here is the most recent Riparian Forecast.