Outfall Flow Analysis for the Oswego Canal and Blue Heron Canal

DRAFT REPORT Outfall Flow Analysis for the Oswego Canal and Blue Heron Canal Prepared for: City of Lake Oswego, Oregon Prepared by: Pacific Water Resources, Inc. January 31, 2008 We Think the World of Water PACIFIC WATER RESOURCES, INC. 4905 S.W. Griffith Drive, Suite 200, Beaverton, Oregon 97005 www.pacificwr.com info@pacificwr.com 503.671.9709

DRAFT REPORT Outfall Flow Analysis for Oswego Canal and Blue Heron Canal Pacific Water Resources, Inc. (PWR) January 31, 2008 Background An analysis of expected peak flows for outfalls mapped in the Oswego Canal and Blue Heron Canal areas was performed for the City of Lake Oswego by Pacific Water Resources, Inc. (PWR) to support the City s planning for construction of the Oswego Lake Interceptor Sewer (OLIS) and, specifically for the purposes of this analysis, an existing trunk sewer and associated laterals located within these areas. Outfall Flow Analysis Peak flows were modeled separately for the summer season (April through October) and the winter season (November through March). These flows were modeled using the King County (Washington) HYD program using the Santa Barbara Urban Hydrograph (SBUH) method. Input data developed as part of this analysis included: Expected 24-hour peak rainfall depths for the summer and winter seasons Areas, imperviousness, and soil type draining to each outfall Estimated travel time (time of concentration) for runoff to reach the outfall The results are shown on the following three pages. Each page includes a figure that maps the location of each outfall based on map layers from the City. The figures include the City s outfall ID and the outfall diameter. Outfall basin areas are based on the City s subbasin delineation. Outfall diameters are from the City s storm line GIS mapping. Some outfall diameters were estimated as matching adjacent pipe diameters and are noted by Est. A few other outfall diameters were unknown as no adjacent pipe diameters were provided; these are noted by Unk The maps include subbasin boundaries with names matching the outfall IDs. The delineation includes a number of Direct Drainage areas that have no outfall plus the UPSTREAM area that drains into the Oswego Canal construction zone from upstream of Bryant Road. Below each figure is a table summarizing the flows for those outfalls shown in the figure. The table includes the subbasin name (which usually matches the outfall ID), the outfall diameter (in inches), the total area (in acres) and impervious percentage draining to the outfall. Following are the flows modeled for each outfall for the winter (November through March) and summer (April through October) seasons. Flows are modeled for the 1-year-average, 2-year, 5-year, 7-year, and 10-year events. Analysis of rainfall depths is provided in the next section. 1233/outfall-flow-analysis.doc Page 1 Pacific Water Resources, Inc.

Figure 1 Outfalls to the Oswego Canal and Blue Heron Canal (northern area) Summer Season Peak Flow (cfs) Winter Season Peak Flow (cfs) Subbasin Diam (in) Model Acres Mia 1/Year 1/2 Yrs 1/5 Yrs 1/7 Yrs 1/10 Yrs 1/Year 1/2 Yrs 1/5 Yrs 1/7 Yrs 1/10 Yrs Oswego Canal (north of South Shore Blvd.) Direct Runoff (na) OBAY 4.6 61% 0.53 0.68 0.94 1.05 1.17 0.9 1.13 1.51 1.55 1.59 OS0200 10 C200 2.0 30% 0.1 0.13 0.19 0.22 0.26 0.18 0.25 0.36 0.38 0.39 Oswego Canal Direct Runoff (na) OCAN 42.0 36% 2.69 3.89 5.94 6.9 7.88 5.63 7.55 10.65 11 11.36 OS0300 12 C300 6.1 34% 0.33 0.49 0.75 0.87 1 0.71 0.96 1.35 1.4 1.44 Kelok Bay Direct Runoff (na) KBAY 9.0 60% 1.02 1.32 1.81 2.04 2.27 1.73 2.19 2.92 3.01 3.09 OL0720 10 L720 2.1 33% 0.12 0.15 0.22 0.26 0.3 0.21 0.29 0.41 0.43 0.44 ER0100 15 E100 13.2 34% 0.62 0.82 1.23 1.43 1.65 1.17 1.58 2.26 2.34 2.42 Blue Heron (north of South Shore Blvd.) Direct Runoff (na) BBAY 5.7 65% 0.81 1.04 1.42 1.6 1.78 1.37 1.72 2.26 2.32 2.39 OL0710 12 L710 1.4 36% 0.1 0.13 0.19 0.23 0.26 0.18 0.25 0.36 0.37 0.38 BHB1 12 BHB1 1.3 38% 0.09 0.11 0.16 0.19 0.22 0.16 0.21 0.3 0.31 0.32 Blue Heron Canal Direct Runoff (na) BCAN 29.6 43% 2.72 3.78 5.59 6.42 7.27 5.32 6.99 9.64 9.95 10.26 BC1 Est 12 B1XX 0.9 33% 0.05 0.07 0.1 0.12 0.14 0.1 0.13 0.19 0.2 0.2 BC0200+0210 30 B200 94.9 25% 4.77 7.57 12.32 14.54 16.85 11.6 16.07 23.35 24.2 25.04 1233/flow-duration-analysis.doc Page 2 Pacific Water Resources, Inc.

Figure 2 Outfalls to the Oswego Canal and Blue Heron Canal (middle area) Summer Season Peak Flow (cfs) Winter Season Peak Flow (cfs) Subbasin Diam (in) Model Acres Mia 1/Year 1/2 Yrs 1/5 Yrs 1/7 Yrs 1/10 Yrs 1/Year 1/2 Yrs 1/5 Yrs 1/7 Yrs 1/10 Yrs Oswego Canal OS0400 12 C400 0.5 40% 0.04 0.06 0.09 0.1 0.12 0.09 0.11 0.15 0.16 0.16 OS0500 18 C500 17.2 34% 0.84 1.11 1.65 1.93 2.22 1.56 2.12 3.06 3.17 3.28 OS0600 Est 12 C600 6.2 34% 0.37 0.55 0.84 0.97 1.1 0.79 1.06 1.48 1.53 1.58 Blue Heron Canal BC0220 Unk. B220 48.4 25% 1.99 3.12 5.09 6.03 7 4.79 6.67 9.75 10.11 10.47 BC0300 12 B300 3.4 32% 0.19 0.26 0.39 0.46 0.53 0.37 0.5 0.73 0.76 0.78 BC0400 8 B400 0.8 38% 0.06 0.08 0.11 0.13 0.15 0.11 0.14 0.21 0.21 0.22 BC0500 15 B500 20.6 26% 0.96 1.5 2.43 2.86 3.31 2.28 3.16 4.59 4.75 4.92 BC0600 8 B600 3.9 33% 0.28 0.42 0.64 0.75 0.85 0.61 0.81 1.14 1.17 1.21 1233/flow-duration-analysis.doc Page 3 Pacific Water Resources, Inc.

Figure 3 Outfalls to the Oswego Canal and Blue Heron Canal (southern area) Summer Season Peak Flow (cfs) Winter Season Peak Flow (cfs) Subbasin Diam (in) Model Acres Mia 1/Year 1/2 Yrs 1/5 Yrs 1/7 Yrs 1/10 Yrs 1/Year 1/2 Yrs 1/5 Yrs 1/7 Yrs 1/10 Yrs Oswego Canal OS0700 Est 18 C700 12.8 34% 0.63 0.82 1.19 1.38 1.59 1.13 1.52 2.19 2.27 2.35 OS0800 Est 12 C800 11.3 34% 0.62 0.82 1.23 1.44 1.66 1.17 1.59 2.29 2.38 2.46 OS0900 12 C900 0.8 25% 0.03 0.05 0.08 0.09 0.11 0.07 0.1 0.15 0.16 0.17 OS1100 33 C11H 107.1 30% 4.68 6.41 10.01 11.8 13.7 9.44 13.05 19.13 19.84 20.56 UPSTREAM (BRYANT) (na) BRYT 362.2 22% 10.21 15.42 25.69 30.78 36.18 24.07 34.35 51.77 53.81 55.88 Blue Heron Canal BH0100+0200+0300 24 B100 89.6 24% 4.22 6.78 11.15 13.2 15.34 10.49 14.62 21.36 22.14 22.92 BC0700 Est 8 B700 5.4 33% 0.38 0.58 0.88 1.02 1.16 0.83 1.11 1.55 1.6 1.65 BC0800 8 B800 5.1 33% 0.37 0.55 0.85 0.99 1.13 0.8 1.08 1.52 1.57 1.62 BC0900 8 B900 1.8 33% 0.13 0.2 0.3 0.35 0.4 0.29 0.38 0.53 0.55 0.57 BC1000+1010 24 B10H 28.0 25% 1.47 2.35 3.83 4.52 5.23 3.6 4.99 7.25 7.51 7.77 BC1100 Unk. B11H 11.1 31% 0.67 1.02 1.59 1.86 2.13 1.51 2.04 2.88 2.98 3.08 1233/flow-duration-analysis.doc Page 4 Pacific Water Resources, Inc.

Modeling these flows using the SBUH method required the following inputs: Pervious-area SCS Curve Number Pervious area (acres) Impervious area SCS Curve Number (always 98) Impervious area (acres) Travel time (time of concentration, Tc) The pervious area curve numbers were based on a GIS analysis of subbasin boundaries, land use, and soil hydrologic group. GIS map layers were provided by the City and then refined by PWR to reflect two small outfalls on Blue Heron Canal and to divide the direct-drainage areas where crossed by South Shore Blvd. The GIS analysis subdivided each subbasin into areas of each hydrologic soil type (B-, C-, and D-). Half of the B- and C-type soil areas were modeled as urban (type C with lawns), and the remaining B- and C-type soils were modeled as brushcovered. Table 1 lists the input values that were used. Table 1 SBUH Hydrologic Model Input Values Area by Category (Acres) Runoff Model Input Outfall ID Total Imperv B Brush C Brush D Perv. Urban Perv Ac. Perv CN Imp Ac. Imp CN Tc Mins Curve #s: 100 72 81 86 86 Oswego Canal "Bay" Direct Runoff 4.6 2.8 0.9 0.0 0.0 0.9 1.8 79 2.8 98 19 OS0200 2.0 0.6 0.7 0.0 0.0 0.7 1.4 79 0.6 98 30 Oswego Canal Direct Runoff 42.0 15.1 6.5 0.0 13.9 6.5 26.9 83 15.1 98 24 OS0300 6.1 2.1 0.6 0.0 2.8 0.6 4.0 84 2.1 98 35 OS0400 0.5 0.2 0.0 0.0 0.3 0.0 0.3 86 0.2 98 21 OS0500 17.2 5.8 4.6 0.0 2.2 4.6 11.4 80 5.8 98 39 OS0600 6.2 2.1 0.0 0.0 4.1 0.0 4.1 86 2.1 98 35 OS0700 12.8 4.4 4.2 0.0 0.0 4.2 8.4 79 4.4 98 40 OS0800 11.3 3.8 3.3 0.0 1.0 3.2 7.5 80 3.8 98 29 OS0900 0.8 0.2 0.2 0.0 0.2 0.2 0.6 81 0.2 98 27 OS1100 107.1 31.7 25.7 0.0 23.9 25.8 75.4 81 31.7 98 37 UPSTREAM 362.2 79.7 52.4 59.7 58.2 112.1 282.5 82 79.7 98 53 Kelok Bay Direct Runoff 9.0 5.4 1.8 0.0 0.0 1.8 3.6 79 5.4 98 19 OL0720 2.1 0.7 0.7 0.0 0.0 0.7 1.4 79 0.7 98 28 ER0100 13.2 4.5 3.9 0.0 0.9 3.9 8.7 80 4.5 98 43 Blue Heron Bay Direct Runoff 5.7 3.7 1.0 0.0 0.0 1.0 2.0 79 3.7 98 10 OL0710 1.4 0.5 0.4 0.0 0.0 0.5 0.9 80 0.5 98 17 BHB1 1.3 0.5 0.4 0.0 0.0 0.4 0.8 79 0.5 98 24 Blue Heron Canal Direct Runoff 29.6 12.8 4.4 0.4 7.4 4.6 16.8 82 12.8 98 12 BC1 0.9 0.3 0.3 0.0 0.0 0.3 0.6 79 0.3 98 24 BC0200+0210 94.9 23.9 0.4 33.3 3.9 33.4 71.0 84 23.9 98 21 BC0220 48.4 12.1 0.0 17.7 0.8 17.8 36.3 84 12.1 98 34 BC0300 3.4 1.1 1.0 0.0 0.3 1.0 2.3 80 1.1 98 24 BC0400 0.8 0.3 0.2 0.0 0.0 0.3 0.5 80 0.3 98 18 BC0500 20.6 5.4 0.7 5.4 2.9 6.2 15.2 84 5.4 98 28 BC0600 3.9 1.3 0.0 0.0 2.6 0.0 2.6 86 1.3 98 21 BH0100+0200+0300 89.6 21.4 0.3 33.0 1.7 33.2 68.2 84 21.4 98 22 BC0700 5.4 1.8 0.0 0.0 3.6 0.0 3.6 86 1.8 98 22 BC0800 5.1 1.7 0.5 0.3 1.8 0.8 3.4 84 1.7 98 15 BC0900 1.8 0.6 0.0 0.0 1.2 0.0 1.2 86 0.6 98 20 BC1000+1010 28.0 7.0 0.0 8.0 4.9 8.1 21.0 84 7.0 98 18 BC1100 11.1 3.4 0.0 1.4 4.9 1.4 7.7 85 3.4 98 24 1233/flow-duration-analysis.doc Page 5 Pacific Water Resources, Inc.

Rainfall Depth Analysis As part of this analysis, PWR estimated 24-hour rainfall depths separately for the winter (November through March) and summer (April through October) seasons. The primary rainfall source used was the City of Portland HYDRA gage at PCC Sylvania which provided data for October 1998 through May 2004 and March 2005 through September 2007. A second rainfall source was needed to develop longer-term rainfall statistics. PWR used the rainfall record developed for the Damascus area that used a combination of the HYDRA gage at Pleasant Valley School supplemented with data adjusted and corrected from the NOAA Portland Airport gage. This second rainfall source had data for October 1948 through December 2004. This second source was used because PWR had thoroughly reviewed it as part of an earlier project for Clackamas County. The Pleasant Valley rainfall was scaled uniformly by 82% to account for differences in rainfall depths and intensities between the Pleasant Valley (also called WES ) and PCC Sylvania rainfall gages. This adjustment was based on two comparisons which both yielded the same result. First, accumulated rainfall depths from both gages were compared for the overlapping period of October 1998 through May 2004 and February 2005 through December 2007. Also compared was the Pleasant Valley rainfall scaled by a uniform 82% factor. Figure 4 shows the result of this comparison and showing a good fit for the 82% scaling factor. Figure 4 Analysis of 6 Years of Accumulated Rainfall 1233/flow-duration-analysis.doc Page 6 Pacific Water Resources, Inc.

A second comparison was made for peak 24-hour rainfall intensities. The hourly rainfall data from each gage was grouped into rainfall events separated by at least 6 hours without rainfall. The peak 24-hour rainfall intensity was calculated for each event. Because the Sylvania gage was missing data for much of 2004, seven years of data (October 1998 September 2003 and October 2005 through September 2007) were used for this comparison. Figure 5 graphs this comparison, showing a good fit for both smaller and larger events using the 82% scaling factor. PWR developed seasonal rainfall depths for the PCC Sylvania rainfall supplemented by data for Pleasant Valley scaled by 82% for October 1948 through September 1998 and for May 2004 through February 2005, resulting in a 59-year continuous rainfall record (October 1948 through September 2007). Peak 24-hour rainfall intensities were evaluated separately for the winter (November through March) and summer (April through October) seasons. The rainfall was grouped into events based on minimum rain-free separation periods of at least six hours. Peak 24-hour rainfall intensities were then calculated for each event. When sorted by rainfall intensity, the average number of events per year can be calculated. Figure 6 shows the resulting 24-hour peak rainfall intensities compared to the number of events per year of at least that size event. Figure 5 Analysis of Peak 24-Hour Rainfall Data 1233/flow-duration-analysis.doc Page 7 Pacific Water Resources, Inc.

Figure 6 Peak 24-Hour Rainfall Intensities for PCC Sylvania Table 2 lists the resulting rainfall depths for the winter (November through March) and summer (April through October) seasons. Table 2 Peak 24-Hour Rainfall for Lake Oswego Full Winter Summer Event (Year) Events/Year Year Nov-Mar Apr-Oct 1 1 1.7 1.6 1.05 2 0.5 2 1.9 1.3 5 0.2 2.4 2.35 1.65 7 0.14 2.5 2.4 1.8 10 0.1 2.65 2.45 1.95 1233/flow-duration-analysis.doc Page 8 Pacific Water Resources, Inc.

The expected rainfall depths were obtained using Figure 7, which includes the information from Figure 6 but uses a logarithmic scale. This makes it easier to smooth the curve of modeled rainfall. Expected depths were both rounded to the nearest 0.05-inch and were sometimes increased by an additional 0.05-inch to smooth over unevenness in the data. Figures 6 and 7 also show the full-year statistics. The full-year rainfall depths are only slightly higher than the winter depths because most of the larger events were in the winter months of November through March. Figure 7 Modeled Peak 24-Hour Rainfall for Lake Oswego 1233/flow-duration-analysis.doc Page 9 Pacific Water Resources, Inc.