Carmel River Watershed: Robinson and San Clemente Creeks Flow Duration Analysis
Robinson Creek joins Carmel River relatively low in the watershed. Its watershed is approximately 14 km2 in area. Its aspect is to the north and lies in a narrow steep canyon. The Robinson Creek watershed has a higher higher soil erosion index than San Clemente Watershed. San Clemente Creek is located relatively high in the Carmel watershed, above San Clemente Dam. Its watershed is approximately 40 km2 in area and has an east-northeast aspect. San Clemente Watershed has a more diverse range of slopes than Robinson Watershed. Locations of the two watersheds are in Figure 2 below.
Figure 2. Location of Robinson Creek (top highlight) and San Clemente Creek (lower highlight) watersheds within the overall Carmel River Watershed.
Robinson Creek’s flow duration curve (FDC) indicates there is flow about 45% of the time. Overall, the smooth FDC indicates a natural, unregulated flow regime. While smooth, the FDC does curve steeper than the classic straight unregulated FDC, which may just be an indication that no specific flow lasts for a long time in the steep, narrow channel. There is a steeper part of the curve during for high flows between 4 and 7 m3/s, suggesting that these flows are less common than flows above 7 m3/s relative to what might be expected under a fully natural flow regime. There is a slightly flat section of the curve from one to 4 m3/s, in the top 1% of flow magnitudes, indicating these size flows occur more frequently than might be expected under a natural flow regime. The steep drop in the low flow section indicates the stream rapidly loses flow as the flow season is ending, and that a persistent source of summer baseflow does not exist.
San Clemente Creek’s FDC shows there is flow almost year round. The smoothness and relatively flat line shows a natural, unregulated flow regime. There are some anomalies at very high flows in the 7 to 11 m3/s area. The very flat section around 9 m3/s may indicate gage failure, estimated data, or some other unnatural phenomenon. The very steep part around 10 m3/s and then flat part around 10.5 m3/s indicates unusual flow regimes. Perhaps at these flows some other flow path becomes available or there is some type of structure influencing flow like a culvert or bridge.
Comparison of the two curves show's that San Clemente Creek experiences consistently higher volume flow and maintains flow through the year much more than Robinson Creek. This makes sense as it has a larger area and lies higher in the watershed where more rainfall occurs. Low-flow loss to an aquifer may also be more prevalent at Robinson Creek, given its proximity to lower Carmel Valley. Overall, San Clemente Creek exhibits more of a natural unregulated FDC as seen in the flatter line. Low flows do not last long in Robinson, and they change more gradually in San Clemente indicating longer runoff/collection time or baseflow.
Comparison of the two curves show much longer flow regime at higher creek in watershed (San Clemente), and flow only half the year at Robinson. Both curves have inflections at the highest flows (~0.1% exceedance), which warrant further investigation. Neither stream shows strong sign of management or control structures, but low-flow loss to aquifers may be a factor influencing the frequency of no-flow conditions.