St. Clair River Conveyance Change 2007 to 2012

Transcription

1 St. Clair River Conveyance Change 2007 to 2012 Morphologic Change in the St. Clair River Conveyance Change Report U.S. Army Corps of Engineers, Detroit District Great Lakes Hydraulics and Hydrology Office July 27, 2016

2 Summary Swath bathymetry of the main stem of the St. Clair River was collected in 2007 and again in 2012, providing the data sets required for a thorough analysis of conveyance change. Conveyance change in the St. Clair River is examined through multiple methods and models. Each method and model are explored to gain a sense of how the conveyance capacity of the river may be changing. Depth change and cut-fill analyses with and without accounting for survey tolerance show change in the river but net change is minimal especially after accounting for survey uncertainties. Hydrodynamic modeling of the same discharge/water level scenarios in the 2007 geometry versus the 2012 geometry also show minimal changes in conveyance, with these differences being well within survey and numerical modeling tolerances. However, there is a spatial trend of apparent increased conveyance on the upper half of the river between 2007 and 2012 that deserves close monitoring. Introduction The International Joint Commission s International Upper Great Lakes Study (2009) highlighted the importance of conveyance change monitoring in the St. Clair and Detroit rivers, as the conveyance capacity of those rivers has a large impact on the water levels of Lakes Michigan, Huron, and Erie. The U.S. Army Corps of Engineers, Detroit District has since developed an operational plan to monitor the conveyance capacity of these connecting channels through regular bathymetric data collection and analysis. One of the datasets necessary to accomplish this mission is the regular collection of swath bathymetry in the rivers and delta. These data were collected in 2007 and 2012 on the St. Clair River and in 2012 on the Detroit River. Currently, the main stem of the St. Clair River is the only connecting channel with multiple swath bathymetry surveys. Details on these data sets are below and compiled in Bennion and Calappi (2015). Existing Studies and Data Repeat multibeam bathymetric survey data were collected in 2007 and 2012 on the St. Clair River by the U.S. Army Corps of Engineers and preliminarily analyzed. Generally, the extents of these surveys cover the main stem of the river from Fort Gratiot to Algonac, Figure 1. The 2007 data are provided on a 1.5 meter grid and is comprised of approximately 13 million points. The 2012 data were provided on a 0.6 meter grid and have more than 100 million points covering the same general extents. Due to the lack of swath bathymetry in the St. Clair River Delta, neither Bennion and Calappi (2015) nor this analysis examine conveyance change originating in the delta.

3 Figure 1: St Clair River

4 Swath bathymetry covering the main stem of the St. Clair River, St. Clair Delta and Detroit River are expected to be collected on a five to seven year rotation and similarly analyzed with depth change/cut-fill comparisons and hydrodynamic models. Similar analyses will be extended through the St. Clair River Delta and the Detroit River upon collection of multiple swath bathymetry data sets. The initial portion of the conveyance change analysis (Bennion and Calappi, 2015) was based on depth change/cut-fill analysis and total survey uncertainty with the goal to quantify geomorphic changes in the river. Based on cut-fill analysis, Bennion and Calappi (2015) summarized an average of m of depth gain (degradation) over the entire river if survey uncertainty is disregarded. When comparing volumes, a net loss of 273,000 m 3 of material was calculated between 2007 and However, when depth change analysis is restricted to data greater than the survey tolerance, a 0.5 m of depth loss (aggradation) and a net gain of 81,000 m 3 of material was calculated for the same time period. The remaining survey area after removing the areas inside the survey uncertainty is too small to be considered representative of the river. While this volume and depth change analyses are useful indicators, further analysis was required to determine the impacts of these changes on the overall conveyance of the river. Model Development In addition to the bathymetric change analysis between the 2007 and the 2012 surveys, a two dimensional hydraulic model was developed to examine changes in water surface elevation for the same flow conditions on the different geometries. Differences in water surface elevations are examined throughout the main stem of the St. Clair River for patterns and signs of conveyance change. The geometry for the hydraulic models are defined by merging several data sets together. The model geometry incorporates bathymetry from the NOAA Great Lakes Bathymetry model, the USGS 1/3 rd arcsecond DEM, as well as data collected by the U.S. Army Corps of Engineers, Detroit District. The navigation channels in Lake St. Clair and Lake Huron are regularly surveyed by the U.S. Army Corps of Engineers, Detroit Area Office using multibeam technology. These surveys are included in the overall model geometry. The survey defining the St. Clair River Delta is single beam performed by contractor and dates from The remaining geometry comes from the NOAA Great Lakes Model and generally fills in the large portions of Lake St. Clair and Lake Huron included in the model domain. The 2007 and 2012 model geometries share the same data sources outside of the main stem of the St. Clair River. The 2007 main stem of the St. Clair River survey data were removed from the overall geometry and replaced with the 2012 main stem of the St. Clair River survey data to form the new geometry analyzed for conveyance change.

5 All 13 million survey points from the 2007 survey were used in the mesh development for the 2007 model. However, the 100 million points from the 2012 survey were thinned to a more manageable size to facilitate efficient mesh development. The data were filtered using an adjacent normal filtering scheme. This scheme removes points from areas of the channel with locally constant gradients while preserving high point density in critical areas of changing elevation necessary to capture the unique geometry of the channel. The resulting data set from 2012 had 39 million points. The Adaptive Hydraulics (AdH) model extends from approximately Lakeport on Lake Huron to Windmill Point on Lake St. Clair, Figure 2. The upstream model extent was chosen to be reasonably well removed from the head of the river. The model mesh has approximately 130,000 nodes with a grid resolution of 400 m at the upper end of Lake Huron and 30 m in the St. Clair River; maximum grid resolution in Lake St. Clair is on the order of 1500 m. The same mesh with the same friction values, eddy viscosity, iteration tolerances and wetting and drying parameters were used in the 2007 and 2012 model. Friction values ranged from to and the Smagorinsky method for eddy viscosity was used with a constant value of 0.1 used throughout the model. The AdH model was calibrated from July through August 2007 using the 2007 geometry. This was chosen because it coincides with the collection of the bathymetry and acoustic Doppler current Profiler (adcp) data are available to evaluate the flow splits through the delta. The models were calibrated under dynamic flow conditions with a flow hydrograph upstream and tail-water at Windmill Point (NOAA gauge ). The model was forced with hourly discharge values developed from the Fort Gratiot (NOAA gauge ) and Algonac (NOAA gauge ) stage-fall-discharge relationship developed in 2009 (Fay and Kerslake, 2009). Calibration results are shown in Figure 3 for three gauges along the river, Dunn Paper (NOAA ), Dry Dock (NOAA ) and St Clair State Police (NOAA ).

6 Figure 2: AdH model domain

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8 Figure 3: Water Surface Elevations. Calibration at NOAA gages for 01-Jul-2007 to 31- Aug The vertical Y-axis is the water surface elevations in meters, and the horizontal X-axis is the hours of the calibration run. Conveyance Change Analysis High and low flows were modeled at steady state to determine if conveyance capacity of the river changed between the 2007 survey and 2012 survey. Modeled flows in this analysis were chosen based on historic monthly average discharge values from 1918 through The 90 th and 10 th percentile flow for each month was computed, the month with the highest, 90 th percentile flow was chosen for conveyance change analysis. On the St. Clair River, August has the highest 90 th percentile flow. The most recent occurrence of the 90 th percentile flow in August, was in This flow was used as the upstream boundary condition. The downstream boundary condition is the monthly average water level at Windmill Point (NOAA gauge ) from August Steady state modeled output were compared to monthly average water levels at gauge locations along the St. Clair River. The conveyance change analysis is performed by examining differences in modeled water surface elevation resulting from geometric changes in the main stem of the river. Decreased water surface elevation for the same discharge is indicative of an increased conveyance capacity. A similar analysis was done for the low flows. Of the ice free months, May has the lowest 10 th percentile flow at 4,770 cms; however, this discharge never occurred in the monthly mean flow

9 record for May, so a corresponding monthly mean tailwater elevation could not be matched to the discharge. Observed conditions were desired for this analysis. In order to use an observed combination of sufficiently low flow and water levels to evaluate conveyance change on the low end of the flow spectrum, the 15 th percentile flow was used, which occurred in May of The high flow scenario used a discharge of 6,170 cms and water level of m, IGLD85. The low flow scenario used a discharge of 4,830 cms and a water level of m, IGLD85. The AdH modeled differences between the 2007 and 2012 geometries are shown at water level gauge locations along the river in Table 1. Under the low flow scenario, the two dimensional model has a maximum difference in water surface elevation of 8mm between the two geometries with the 2012 geometry yielding lower water surface elevations. Similar results are noted for the high flow scenario. Lower water surface elevation in 2012 for the same boundary conditions could suggest an increase in conveyance, however, due to the low magnitude in change in comparison to the uncertainty in the numerical model and bathymetric survey, it is premature to conclude conveyance has increased. Table 1: Conveyance Change Water Surface Elevation Change Results Location AdH WSE (m)- Low Q AdH WSE (m) - High Q Fort Gratiot Dunn Paper Point Edward MBR Dry Dock SC Police Port Lambton Algonac SCS Figure 4 shows a more holistic view of conveyance change and examines spatial changes and trends in water surface elevation between the two geometries. It also shows a water surface elevation for the 2012 geometry is up to 1cm lower than the 2007 geometry in the upper half of the river, especially for the high flow scenario. The magnitude of the change in water surface elevation is small, especially compared to uncertainty associated with the bathymetry, model and rating equations used to determine the upstream boundary condition. However, given the spatial trend of a lower water surface elevation, careful monitoring is warranted. In addition to using the best calibration parameters for Manning s n, a sensitivity analysis was done. The model is discretized into 21 separate material zones with the potential for each zone to have a different Manning s value. Manning values ranged from to The Manning n values were all increased by ten-percent and the conveyance change analysis was repeated.

10 Another sensitivity test on Manning s n was performed, this time reducing the optimal values by ten-percent and performing the conveyance change analysis again. All three versions of the conveyance change analysis show similar spatial trends with the same magnitude of water surface elevation differences between the 2012 geometry and the 2007 geometry. Figure 4: Change in water surface elevations between the 2007 and 2012 model geometries based on high flow (left) and low flow (right). Changes are reported in meters and range from m to 0.01m in both figures. Given both versions of the model (2007 and 2012) are forced with the same discharge and tail water condition, examining differences in water levels is the appropriate, independent comparison between the two models. However, quantifying the geometric changes in terms of discharge makes more intuitive sense. So the model was run to steady state for both high and low flow conditions. The hydraulic parameters necessary to compute change in flow using both the stage-fall-discharge relationships based on NOAA gauges and at Fort Gratiot and Algonac, respectively and the index velocity relationship developed for USGS gauge at Port Huron were extracted from both the 2007 and 2012 models. Based on the stage-fall-discharge relationship, shown in equation 1, there would be a predicted change in flow of 60 cms with more flow occurring in the model built on the 2007 geometry. This

11 was the case for both the high and low flow scenario. This seems to contradict data represented in Figure 4, which shows slightly lower water levels for 2012 when compared to 2007 over the upper reach of the river, indicating a conveyance increase. However, it is important to note that the root mean square error of equation 1 is 140 cms, (Fay and Kerslake, 2009), and the change in flow of 60cms is quite small and well within the uncertainty of the equation itself so it is difficult to draw any conclusions from this apparent flow change. In equation 1 below, Q is total discharge, AL is the water surface elevation at Algonac and FG is the water surface elevation at Fort Gratiot. QQ = (AAAA ) (FFFF AAAA) Eq. 1 Similarly, the parameters needed to estimate discharge based on the index velocity method developed by the U.S. Geological Survey and Water Survey Canada and shown in equations 2 and 3 were extracted from the model for both the 2007 and 2012 geometries. These equations are developed and shown in English units. Changes in discharge were 100 cms for the high flow scenario and 60 cms for the low flow scenario. However, using this method, the 2012 geometry conveyed more flow, which is more consistent with figure 4. The root mean square error for the index velocity method is approximately 110 cms. Equation 2 is used to estimate the average cross section velocity while equation 3 is used to estimate the total flow area based on the water level gauge operated by Department of Fisheries and Oceans gauge11940 at Point Edward. Total discharge is obtained by multiplying equation 2 and 3 together. The estimated, average velocity in the cross section is determined by measuring the velocity (Vindex) over a 40 meter portion of the river 40 to 80 meters from the shoreline. The depth-averaged velocity from a similar location from within the model domain is used in this implementation of the index-velocity method for discharge. However, the index-velocity method is not developed from depth-averaged velocities, but this simplification must be accepted if changes in flow are to be explored in this manner. VV cccccccccc ssssssssssssss aaaaaaaaaaaaaa = VV iiiiiiiiii Eq. 2 AAAAAAAA = PPPP , Eq. 3 Due to the uncertainties associated with the bathymetric surveys, numerical models, hydraulic measurements and the regression equations Eq. 1 to Eq. 3, it is unclear if the conveyance capacity in the St. Clair River has changed over this period. However, any change during this period was small in magnitude. The spatial distribution of lower water surface elevations based on the 2012 geometry suggests minor scouring in the upper reach of the river and further conveyance change monitoring is recommended. This analysis will be repeated when new bathymetry is collected, most likely in the time frame. Future analysis will not only look at potential conveyance change between the most recently collected bathymetry, but also the potential gradual changes back to 2007.

12 REFERENCES Bennion, D. and Calappi, T Morphologic Change in the St. Clair River Phase 1 Report, unpublished Fay, D and kerslake, H Development of New Stage-Fall-Discharge Equations for the St. Clair River, International Joint Commission Holtschlag, D.J. and Hoard, C.J., 2009 Detection of conveyance changes in St. Clair River using historical water-level and flow data with inverse one-dimensional hydrodynamic modeling: U.S. Geological Survey Scientific Investigations Report , 39 p. International Upper Great Lakes Study Board, 2009, Impacts on Upper Great Lakes Water Levels: St. Clair River, Final Report to the International Joint Commission, 224 p.