Difference between revisions of "Carmel River Watershed: Pine and Cachagua Creeks Flow Duration Analysis"

Revision as of 10:32, 24 February 2009

File:PineCreek Flow Duration Curve.pdf

Hydrologic setting

Pine Creek is a tributary to the Carmel River and is located upstream from the San Clemente Dam. The confluence with the Carmel River is a site of a California Department of Fish & Game (CDFG) project to improve steelhead spawning habitat^[1]. Course description here.

Analysis^[2]

The flow duration curve (FDC) for Pine Creek indicates that at the confluence with the Carmel River, the creek flows over 90% of the time. The general smoothness of the FDC is indicative of an unregulated flow regime i.e. there does not appear to any regulation system upstream that would cause any particular flows rates to be more common than slightly higher or lower flow rates.

The FDC for the Reclamation Ditch at San Jon Rd indicates perennial or near-perennial flow. There are inflection points in the curve, indicating some non-natural intervention in the flow regime. Relative to the smooth curve expected of an unregulated stream, steeper parts of the curve correspond to relatively uncommon flows, and flatter parts of the curve correspond to relatively common flows. The curve is steeper between the 20% and 5% quantiles, corresponding to flow rates between about 0.2 and 2 CMS (about 7 and 70 CFS). Another way of putting this is that the Reclamation Ditch FDC is relatively flat out during the driest 80% of the record, indicating that flows during the driest 80% of the record are higher than would be expected if the site were more similar to the Gabilan Creek site.

Comparing the two curves, Gabilan Creek's highest flows (>10 CMS) are higher than the highest flows downstream in the Reclamation Ditch. Vice versa, during the lower flow periods, the Reclamation Ditch carries more flow than Gabilan Creek, which doesn't flow at all during dry weather. These two observations in combination indicate either:

1. diffusion of storm hydrographs i.e. a lowering of storm peak flows and extension of duration of sub-peak flows as one moves downstream
2. and/or, loss of flow due to diversion or infiltration

A combination of both is likely. For example, Carr Lake as able to temporarily store a large volume of storm flow, which is then gradually drained through a culvert. This amounts to diffusion of storm hydrographs. At the same time, the sand- and gravel-bed streams overlying the Salinas Valley aquifer are well known to lose a great deal of water to infiltration.

If only these two mechanisms occurred, we would expect the Reclamation Ditch FDC to dive to zero at some point to the left of the of the Gabilan Creek FDC. However, it stays non-zero through even the driest periods. This suggests a source of flow that is unrelated to direct storm runoff and in-stream flow routing. Potential sources include irrigation tailwater from domestic and agricultural sources, industrial discharges, and basement sump pumping.

Summary

Based on visual comparison of flow duration curves, the Gabilan Creek / Reclamation Ditch system appears to exhibit watershed processes such as:

1. Storm hydrograph diffusion
2. Streambed infiltration
3. Managed streamflow sources (e.g. residential, agricultural, industrial)

References

1. ↑ CDFG Improve Steelhead Passage: Pine Creek Confluence Project Description: http://www.ice.ucdavis.edu/nrpi/NRPIDescription.asp?ProjectPK=7182
2. ↑ An analysis similar to this one was published in the Reclamation Ditch Watershed Assessment and Management Strategy: http://www.mcwra.co.monterey.ca.us/Agency_data/RecDitchFinal/RecDitchFinal.htm

Links

• Gabilan Watershed
• How to save an Excel chart directly to an image file
• Carmel River Watershed: Flow Duration Analyses