L OWER N OOKSACK R IVER P ROJECT: A LTERNATIVES A NALYSIS A PPENDIX A: H YDRAULIC M ODELING PREPARED BY: LandC, etc, LLC
TABLE OF CONTENTS 1 Introduction... 1 2 Methods... 1 2.1 Hydraulic Model... 1 2.2 Model Setup and Development... 1 2.2.1 Existing Conditions... 1 2.2.2 High Flow Model... 2 2.2.3 Low Flow Model... 2 2.2.4 Left Bank Floodplain... 3 2.3 Boundary Conditions... 3 2.4 Model Calibration... 4 2.4.1 High Flow Calibration... 4 2.4.2 Low Flow Calibration... 4 2.5 Model Output... 9 2.6 Post-Processing / Water Surface Elevation Interpolation... 11 3 Assumptions and Limitations... 11 4 References... 12
Appendix A: Hydraulic Modeling Methodology Lower Nooksack River Project: Alternatives Analysis 1 Introduction The primary purpose of this report is to provide an overview of the hydraulic modeling process used to support the Lower Nooksack Restoration Project (LNRP) in addressing existing flood risks and habitat degradation. Hydraulic modeling for this project focuses on the Nooksack River and its floodplain downstream of the City of Ferndale to Bellingham Bay and was utilized to gather the following information: Quantify flood impacts of levee alignments and profiles on the left and right bank to enable evaluation of alternatives. Quantify flood benefit of rehabilitation of the Lummi River diversion structure. Provide water surface elevations to quantify changes in habitat opportunity for target species. Comparisons of hydraulic modeling results of alternative runs were compared and were overlain with LiDAR data from the Lummi Natural Resources (2005) to identify potential flood benefits. Hydraulic modeling results were also input into to the habitat analysis to analyze potential habitat benefits. 2 Methods 2.1 Hydraulic Model Whatcom County s existing Lower Nooksack River hydraulic model was utilized as a starting point for LNRP hydraulic modeling efforts. The Lower Nooksack River hydraulic model was developed using the Full Equations (FEQ), a one-dimensional, unsteady-flow model and consists of flow paths, cross sections, and level pool reservoirs that extend from the location of the former Deming gage just downstream of the confluence of the upper forks of the Nooksack River, to Bellingham Bay, including the overflow corridor from Everson to Sumas. 2.2 Model Setup and Development 2.2.1 Existing Conditions The lower Nooksack River hydraulic model was originally developed for the Flood Insurance Study - preliminary flood insurance mapping during 2012. Since then, several updates had been made for on-going watershed planning and alternative analysis. Most of them occurred in the Reach 4 area near Deming, which encompasses the detail along the Deming Levee and neighboring Christmas Tree Farm located just downstream of the levee. 1
LandC, etc, LLC June 2015 To create the existing conditions model for the project, the Lower Nooksack Model was revised to reflect the Lummi Nation s project of raising Marine Drive between Kwina (Rainbow) Slough and Haxton Way. The Lummi Nation s project was comprised of elevating Marine Drive, lowering the Kwina Slough right bank levee south of Marine Drive, and modeling the Smuggler s Slough culvert with tidegate under Marine Drive. In order to perform comparison on the same bases, especially for the culvert with tidegate under Marine Drive, the Lower Nooksack River hydraulic model was first modified to include a physical channel for the Smuggler s Slough roughly based on the available hydrograph. All earlier calibration events of October 2003, November 2003, November 2004, November 2006, and January 2009 were then re-run to ensure the results of the modified model were comparable to the previous version. Following these modifications and re-run comparisons, the existing condition model for this project was established. 2.2.2 High Flow Model The Lower Nooksack River hydraulic model was developed for floodplain mapping and flood alternative analyses, and it has been calibrated for larger flood events (Franz 2005, Franz 2012). Prior to this project, it had not been tested for low flow events. In order to evaluate the restoration benefits during mean annual flows and the geomorphological implications of different scenarios based on mean flows and annual flood events more realistically, a separate model for the low flow events was created. By doing so, it enables the continued use of the long-time calibrated model for larger floods and maintains the results of earlier analyses. 2.2.3 Low Flow Model A low flow model was created based on the general finding of limited bathymetry measurements obtained from United States Geological Survey (USGS), which were collected in 2013 (Grossman, unpublished data). Channel cross-sections measured in 2013 (four crosssections collected within the project reach) showed an approximately 1-foot rise in the channel invert elevation compared to nearby 2006 surveyed cross-sections. There were far more crosssections gathered during 2006, which were used with LiDAR data to build the Lower Nooksack River digital terrain model. Cross-sections used in the Lower Nooksack River hydraulic model were cut from the above terrain model. Because the 2013 cross-sections provide limited spatial resolution relative to the 2006 model, rather than changing the model bathymetry to use the 2013 cross-sections directly, the Nooksack main channel bed was simply raised one foot between Marine Drive and I-5 to approximately represent the 2013 conditions. This newly created model was meant to be used for low flow condition only before a complete bathymetry revision is performed. 2
Appendix A: Hydraulic Modeling Methodology Lower Nooksack River Project: Alternatives Analysis 2.2.4 Left Bank Floodplain Channel bathymetry was not available for the left bank floodplain channels (Tennant Creek and the lower portion of Silver Creek). In order to approximate channel dimensions on the left bank, Whatcom County River and Flood Division staff measured the invert of Tennant Creek just downstream from Slater Road and of Silver Creek just upstream from Marine Drive. A simplified, trapezoidal channel with approximated width based on existing conditions and a straight channel profile was then added to the model (for both existing and proposed conditions). 2.3 Boundary Conditions Hydrographs based on historic flood events were developed as inputs to the model to depict flood events over a range of recurrence intervals (Tables 4-1 and 4-2). Input hydrographs at the upstream boundary at Deming are based on the USGS streamflow records at Deming (through water year 2005) and Cedarville (water year 2006 and later) for historic floods, as adjusted during calibration and with a factor applied to the entire hydrograph so the peak of the inflow hydrograph matches the flood frequency estimate for each recurrence interval. Table 4-1. Historic flood events and estimated recurrence intervals with measured flows at Ferndale and modeled flows at Deming Date USGS 12213100 at Ferndale flow (cfs) FEQ flow with routing Deming (cfs) Recurrence Interval 2003 October 39,900 39,374 ~10 yr 2003 November 29,600 25,806 2-4 yr 2004 November 42,300 42,124 10-15 yr 2006 November 38,100 37,933 ~10 yr 2009 January 51,700 53,266 ~25 yr Table 4-2. Flood frequency at Ferndale, per Franz 2005 Recurrence Interval Flow at Ferndale (cfs) 1.01 13,817 1.25 19,631 2 24,918 4 30,837 5 32,609 10 39,599 15 45,147 20 49,115 25 52,222 35 54,838 3
LandC, etc, LLC June 2015 Recurrence Interval Flow at Ferndale (cfs) 50 56,723 75 58,914 100 60,502 150 62,793 200 64,457 300 66,863 400 68,614 500 69,998 The FEQ model also requires a boundary condition for the downstream model boundary at Bellingham Bay. The tidal-data station used for the downstream boundary is Bellingham Bay as defined by the National Ocean Service (NOS); the tides at Bellingham Bay are derived from another station by applying corrections to the record at the reference station as defined by NOS. Flood events evaluated included a 2-4 year event (November 2003), a 10-15 year event (November 2004), and 10-year and 100-year administrative flood events. A typical low flow condition of mean annual flow was also evaluated in conjunction with four fixed tidal conditions (mean higher high water [MHHW], mean high water [MHW], mean low water [MLW], mean lower low water [MLLW]) and a two month-long tidal series (from April 15th to June 15th). The mean annual flow at Ferndale Gage is 3,853 cubic feet per second (cfs). In addition, a winter event, spanning from September 2014 to January 2015 was used to inform the geomorphological analysis. 2.4 Model Calibration 2.4.1 High Flow Calibration Periodically the Lower Nooksack River hydraulic model has gone through extensive calibration for larger flood events since its development (Franz 2005, Franz 2012). When any details were added on to the model, the results of the improved model were compared to the previous ones to ensure that the calibration was still valid. As mentioned in Section 2.2.1, this project went through this process in order to represent the changes that occurred as a result of the inserted channel in Smuggler s Slough in lieu of a slotted channel used originally. 2.4.2 Low Flow Calibration The low flow model was calibrated with September 2014 observations at Ferndale USGS gage and a data logger installed by the Whatcom County River and Flood Division near the confluence of the Nooksack main channel and Kwina Slough. The simulated results were verified using the October 2013 event at the Ferndale USGS gage, as well as the almost 3-month period between November 2014 and January 2015 at the Ferndale USGS gage and the data 4
Appendix A: Hydraulic Modeling Methodology Lower Nooksack River Project: Alternatives Analysis logger at Kwina Slough. The first step of calibration was to adjust the Cedarville / Deming flow (provided by USGS) to reproduce a similar flow hydrograph at the Ferndale gage. Afterwards, the calibration focused on adjusting the roughness of the Nooksack main channel and Kwina Slough distributary within a reasonable range. The following figures provide the results of low flow calibration and verification. 25000 20000 15000 Flow (cfs) 10000 5000 0 9/10/2014 9/12/2014 9/14/2014 9/16/2014 9/18/2014 9/20/2014 9/22/2014 9/24/2014 9/26/2014 9/28/2014 9/30/2014 10/2/2014 10/4/2014 USGS Ferndale Gage Date FEQ Simulated (adjusted*) * Adjusting timing of Deming inflow to match the timing of peak flow at Ferndale gage. Figure A-1 Comparison of Flow at USGS Ferndale Gage (September 2014 - October 2014) 5
LandC, etc, LLC June 2015 28 26 24 22 Elevation (ft) 20 18 16 14 12 9/10/2014 9/12/2014 9/14/2014 9/16/2014 9/18/2014 9/20/2014 9/22/2014 9/24/2014 9/26/2014 9/28/2014 9/30/2014 10/2/2014 10/4/2014 USGS Ferndale Gage Date FEQ Simulated (adjusted) * Adjusting timing of Deming inflow to match the timing of peak flow at Ferndale gage. Figure A-2 Comparison of Elevation at USGS Ferndale Gage (September 2014 - October 2014) 20 18 16 Elevation (ft) 14 12 10 8 6 9/10/2014 9/12/2014 9/14/2014 9/16/2014 9/18/2014 9/20/2014 9/22/2014 9/24/2014 9/26/2014 9/28/2014 9/30/2014 10/2/2014 10/4/2014 Nooksack Data Logger Date FEQ Simulated (adjusted) * Adjusting timing of Deming inflow to match the timing of peak flow at Ferndale gage. Figure A-3 Comparison of Elevation at Nooksack River at Kwina Slough (September 2014 - October 2014) 6
Appendix A: Hydraulic Modeling Methodology Lower Nooksack River Project: Alternatives Analysis 25000 20000 15000 Flow (cfs) 10000 5000 0 4/1/2013 4/3/2013 4/5/2013 4/7/2013 4/9/2013 4/11/2013 4/13/2013 4/15/2013 4/17/2013 4/19/2013 4/21/2013 4/23/2013 4/25/2013 4/27/2013 Date USGS Ferndale Gage FEQ Simulated Figure A-4 Comparison of Flow at USGS Ferndale Gage (March 2013 - May 2013) 28 26 24 22 Elevation (ft) 20 18 16 14 12 4/1/2013 4/3/2013 4/5/2013 4/7/2013 4/9/2013 4/11/2013 4/13/2013 4/15/2013 4/17/2013 4/19/2013 4/21/2013 4/23/2013 4/25/2013 4/27/2013 Date USGS Ferndale Gage FEQ Simulated Figure A-5 Comparison of Elevation at USGS Ferndale Gage (March 2013 - May 2013) 7
LandC, etc, LLC June 2015 25000 20000 15000 Flow (cfs) 10000 5000 0 11/17/2014 11/22/2014 11/27/2014 12/2/2014 12/7/2014 12/12/2014 12/17/2014 12/22/2014 12/27/2014 1/1/2015 1/6/2015 1/11/2015 1/16/2015 1/21/2015 1/26/2015 1/31/2015 Date USGS Ferndale Gage FEQ Simulated Figure A-6 Comparison of Flow at USGS Ferndale Gage (November 2014 - January 2015) 28 26 24 22 Elevation (ft) 20 18 16 14 12 11/17/2014 11/22/2014 11/27/2014 12/2/2014 12/7/2014 12/12/2014 12/17/2014 12/22/2014 12/27/2014 1/1/2015 1/6/2015 1/11/2015 1/16/2015 1/21/2015 1/26/2015 1/31/2015 Date USGS Ferndale Gage FEQ Simulated Figure A-7 Comparison of Elevation at USGS Ferndale Gage (November 2014 - January 2015) 8
Appendix A: Hydraulic Modeling Methodology Lower Nooksack River Project: Alternatives Analysis 20 18 16 Elevation (ft) 14 12 10 8 6 11/17/2014 11/22/2014 11/27/2014 12/2/2014 12/7/2014 12/12/2014 12/17/2014 12/22/2014 12/27/2014 1/1/2015 1/6/2015 1/11/2015 1/16/2015 1/21/2015 1/26/2015 1/31/2015 Date Nooksack Data Logger FEQ Simulated Figure A-8 Comparison of Elevation at Nooksack River at Kwina Slough (November 2014 - January 2015) 2.5 Model Output The FEQ model was used to generate water surface elevation, flow, and velocity at each cross section of every flow path in the model (Figure A-9). An additional flow path was modeled for right bank scenarios that created a new channel between the Nooksack River and Kwina Slough through Slater Slough. Areas without a defined flow direction are treated as level pool reservoirs, which are modeled as a uniform water surface elevation for the area, as shown in Figure A-9. Since FEQ mostly is used as an unsteady flow model, it simulates the entire historical floods or administrative floods. Not only it is capable of generating the peak flow, peak stage and maximum velocity at each cross section along every flow path, a duration analysis can also be performed because it incorporates the complete hydrograph. 9
LandC, etc, LLC June 2015 Figure A-9. FEQ model schematic showing flow-path in blue, cross-sections in black, and level pool reservoir boundaries in pink. Water surface elevation (WSE) was the primary output used in evaluating flood impacts. Flow rates, velocities, and duration of inundation over the roadway were used to inform geomorphic evaluation of risks. Key locations where infrastructure impacts were evaluated include Marietta, 10
Appendix A: Hydraulic Modeling Methodology Lower Nooksack River Project: Alternatives Analysis Marine Drive, and Slater Road. Water surface elevations were compared to existing levee heights and used to design new levees in different locations. The hydraulic analysis was used to evaluate whether a specific alternative is likely to increase or decrease flood damage or affect public safety. When model results indicated that adverse flood impacts would result from a modeled scenario or that a modeled scenario would not have a significant effect on flood risk, the alternative was modified to improve the outcome. Water surface elevation was also the primary output used to develop inputs to the habitat model. The results from the hydraulic model were used to identify habitat characteristics and calculate the area of each habitat type (see Appendix B). 2.6 Post-Processing / Water Surface Elevation Interpolation Water surface elevations, modeled for each alternative under three flooding scenarios and mean annual flow at mean higher high water and mean lower low water, were extrapolated over the project area using an ArcGIS surface interpolation tool. Extrapolation used the inverse distance weighted technique, which interpolates a raster surface from points by averaging the values of sample points in the neighborhood of each processing cell. The closer a point is to the center of the cell being estimated, the more influence it has in the averaging process. Barrier features, such as levees, were added to specify the location of features known to interrupt the surface continuity. Points on either side of the barrier were excluded from each other s region of influence. The interpolated WSE was compared to ground elevation based on LiDAR (Lummi Natural Resources 2005). The projected water depth was calculated as the difference between the WSE and the ground elevation. The change in water depth was calculated as the difference between the WSE under base conditions and under each alternative. 3 Assumptions and Limitations The Lower Nooksack River hydraulic model was first developed early 2000s (Franz 2004). Since then, numerous revisions have been made to improve the model when better information was available (Franz 2005a, 2005b, 2005c, 2012). Details regarding the use and development of the model are described in the series of reports. As discussed above, cross-section data from 2013 (Grossman, unpublished data) indicates that the bed of the Nooksack River has aggraded since the last complete calibration in 2010. This model will continue be updated to reflect updated conditions for future studies. Certain assumptions were made for the complex dynamic system of the Lower Nooksack River. Whereas model cross-sections provide a relatively spatially precise prediction of flow and elevation in the main river channel, as shown in Figure A-9, the right bank area west of 11
LandC, etc, LLC June 2015 Ferndale Road within the project area is treated as a series of level pool reservoirs. The spatial precision within these areas is limited. Theoretical flow inputs are added to the level pool reservoir; these inputs generally represent localized drainage, but they do not reflect calibrated flow. The model also does not account for infiltration within the level pool reservoir areas; therefore, water surface elevations within the level pool reservoir areas are expected to overestimate actual conditions. As noted above, the FEQ model for the Lower Nooksack River is based on cross-sections measured in 2006. More recent cross-sections indicate that the channel bed aggraded by approximately one foot between 2006 and 2013. Since the model results related to the channel bed were more pronounced for low flow events than for high flow conditions, the channel bed elevation was adjusted in the FEQ model to represent mean annual flow conditions. Considering the extensive calibration of the model with 2006 surveyed bathymetry with historical flood events, the 2006 model will continue to be used for the high flow events until the bathymetry is updated and calibrated or additional flood high water marks are collected. A complete set of cross-sections was not available, so the modeling of mean annual flow events represents a best approximation of current bed conditions. Similarly, channel bathymetry was not available for the left bank floodplain channels (Tennant Creek and the lower portion of Silver Creek). Approximate channel dimensions were used on the left bank. In addition, all numerical software comes with its own set of computational limitations. The FEQ model requires making some kind of certain approximations to solve the principles such as geometry and/or the convergence tolerance of solutions. Ground-truthing of results could help rule out anomalous results and reduce the chance of over- or under-design. 4 References Franz, D. 2004. Linsley, Kraeger Associates, Ltd. Lower Nooksack River Unsteady-Flow Model and Analysis of Initial Scenarios Near Everson Whatcom County, Washington. Franz, D. 2005a. Analysis of Selected Scenarios. Linsley, Kraeger Associates, Ltd. Franz, D. 2005a. Calibration Results for 2003 Events. Linsley, Kraeger Associates, Ltd. Franz, D. 2005b. Flood Frequency Analysis at Deming, Ferndale, and Everson. Linsley, Kraeger Associates Ltd. Franz, D. 2012. Calibration of the 2010 FIS Model. Linsley, Kraeger Associates, Ltd. 12