Carmel River Watershed: Potero, Pine and Garzas Creeks Flow Duration Analysis

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Hydrologic Setting

The Carmel River begins in the Santa Lucia Mountains, flowing northwest through the Carmel Valley and drains into the Carmel Lagoon and eventually the ocean at Carmel State Beach. There is a strong precipitation gradiant within the watershed with most of the rain falling in the southern portion in the mountains and less near the mouth of the river at lower elevations. There are two dams in the watershed. The first dam is the San Clemente dam, built in 1921 for the storage of drinking water and flood control. Los Padres dame was built in 1949 to try and slow the loss of capacity in San Clemente dam due to sedimentation. As the Carmel River runs through the Carmel Valley it supplies water to the Carmel Aquifer. This aquifer is the major source of water for the towns of Carmel-by-the-sea, Pebble Beach, Pacific Grove, Monterey and parts of Seaside. The Carmel River and Carmel Lagoon are some of the best remaining steelhead habitat on the central California Coast. Attempting to manage the watershed as a source of municipal water and steelhead habitat has caused it to be one of the most monitored watersheds in central California. There is an extensive network of flow gauges between the US Geological Survey and Monterey Peninsula Water Management District.

Analysis

Pine, Garzas and Potero Creek are three tributaries to the main stem of the Carmel River. Pine Creek is the first gauged tributary with a north draining watershed. It enters the river in the upper portion of watershed between the Los Padres and San Clemente dams. Garzas Creek is also a north draining watershed and enters the river below the USGS gauge at Rosies bridge and above the MPWMD gauge and Don Juan bridge. Potero Creek is the southern most north draining gauged watershed and enters the river very near the downstream USGS gauge.

Each curve has a relatively smooth curve indicative of un-managed watersheds. All three of the tributaries have gone dry sometime between 1992 and 2008.

Pine creek is only dry in drought years with flow being recorded at the site for roughly 92% of the time. The flow at the lower and upper end has a distinctive step pattern. Flows at the lower end of the gauge were estimated for almost three months. From June through December of 1994 the flow was estimated with nearly all of August and September being estimated at 0.01 cfs. The creek spends almost a month of every year flowing at 0.01 cfs before going dry. These periods of estimated flow are not completely representative of natural flow and are represented as unnatural on the duration curve.

Garzas Creek is dry about 49% of the time and Potero Creek is dry 30% of the time. The flow duration of these three tributaries correlates well with the precipitation gradient of the watershed. Pine Creek receives the most precipitation and flows the longest during the year. Potero Creek receives the least precipitation and flows the least. Grazas falls somewhere in the middle.

I did not correct for basin size because I wanted to see if basin size was going to over ride the influence of the precipitation gradient. It did not, Garzas Creek has the largest watershed area and flows nearly 50% less time during the year then Pine Creek.

Summary

Based on flow duration analysis of Pine, Garzas and Potero Creeks the precipitation gradient across the watershed appears to be the major control on the length of time north draining creeks flow per year.

Reference

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