TALLAPOOSA RIVER FLOW ANALYSIS R L HARRIS DAM Downstream to WADLEY GAUGE GEO-TUBES EVALUATION

Transcription

1 TALLAPOOSA RIVER FLOW ANALYSIS R L HARRIS DAM Downstream to WADLEY GAUGE GEO-TUBES EVALUATION November 3, 003

2 Page of INTRODUCTION This report addresses hydraulic analysis of a fourteen mile section of the Tallapoosa River from R L Harris Dam downstream to the USGS gauge at Wadley. This analysis includes modeling of the existing river channel and potential changes to river conditions if geo-tubes are placed in the river channel. Both steady and unsteady conditions are evaluated for flows from 50 cfs up to two unit full gate operation (6,000 cfs) from R L Harris Dam. The U.S. Army Corps of Engineers, Hydrologic Engineering Center s HEC-RAS River Analysis System was used to model the Tallapoosa River. RIVER GEOMETRY The Tallapoosa River is approximately fourteen miles long from R L Harris Dam to the USGS Gauge (044500) at the State Highway Bridge at Wadley. At the middle of this stretch of river there is a Country bridge crossing the Tallapoosa River at the community of Malone. This stretch of river has a moderate slope (about a four foot drop per mile), with many shoals, well defined banks, and a railway line that follows the west bank of the river. In 999, Alabama Power Company acquired twenty-one cross sectional surveys for the seven miles of the Tallapoosa River from R L Harris Dam downstream to the Malone Bridge. The USGS has a cross sectional description at the gauge at Wadley which was utilized along with a tailrace cross section at R L Harris Dam which was obtained from Alabama Power Company plant drawings. No cross sections were obtained of the river channel from Malone downstream to Wadley since reregulation structures downstream of Malone were not considered at that time. Figure depicts the profile of the Tallapoosa River based on the cross sections available in PROFILE OF THE TALLPOOSA RIVER From R L Harris Dowstream to the Wadley Gauge Elevation (msl) Miles Above Wadley Gauge Figure.

3 Page 3 of This past spring, a profile of this seven mile stretch of the Tallapoosa River was obtained to ensure that the cross sections obtained in 999 accurately depicted the river channel. Of primary concern is that pool storages created by possible geo-tubes be precisely described by the cross sectional descriptions. Figure shows that the cross sections which were obtained in 999 do accurately represent the profile of the river channel. 665 PROFILE OF THE TALLPOOSA RIVER From R L Harris Dowstream to the Wadley Gauge Elevation (msl) Miles Above Wadley Gauge Figure. Additional profile data was obtained after the August Adaptive Management Meeting in which discussions of potential reregulation structures downstream of Malone prompted the need of additional channel description. Figure 3 illustrates the additional profile of the Tallapoosa River from Malone downstream to Wadley, which is substantially different from the interpolated river channel which had been utilized in prior HEC-RAS models. Due to this discrepancy, seventeen additional cross sections were obtained this past September in the lower seven mile stretch of the Tallapoosa River. Figure 4 illustrates the complete fourteen mile river channel from both profile data taken and also the 999 and 003 cross sectional surveys.

4 Page 4 of 665 PROFILE OF THE TALLPOOSA RIVER From R L Harris Dowstream to the Wadley Gauge Elevation (msl) Miles Above Wadley Gauge Figure PROFILE OF THE TALLPOOSA RIVER From R L Harris Dowstream to the Wadley Gauge Elevation (msl) Miles Above Wadley Gauge Figure 4.

5 Page 5 of GEO-TUBE CONFIGURUATIONS The ability to consider the entire fourteen mile stretch of the Tallapoosa River allows a different approach to be taken in the configuration of geo-tubes than taken earlier. Earlier configurations had substantially higher structures which were more of a level pool characteristic in which the elevation of the structure and size of the notch in the structure dictated the magnitude and duration of flow from the structure. Now there is the possibility of longer distances between reregulation structures along with longer reregulation pools which increases the ability of providing reregulation without having higher structures in the river channel. With this as the mindset, each of the geo-tube locations selected were limited to five feet in height. Using the profile of Tallapoosa River while trying to locate flat spots in the profile, five geo-tube locations were selected. Geo-tube locations at RM.99, RM5.0 and RM8.7 are designated as primary locations, since they provide the more storage and longer lengths of pool. The notch openings of these geo-tubes were sized such that these three geo-tubes would act in concert to provide the maximum augmentation to river flows. Two smaller geo-tube locations (at RM0.48 and RM.05) were sized to provide additional flow augmentation for extreme low flow conditions. These two smaller sites do not contribute significantly during normal flows conditions for they remain inundated for the majority of the time. Figures 5 and 6 show the location sites in both profile and plan views. Table contains descriptions of the potential geo-tubes evaluated. Figures 7 through show cross sectional view at each geo-tube location. 665 PROFILE OF THE TALLPOOSA RIVER From R L Harris Dowstream to the Wadley Gauge Elevation (msl) Miles Above Wadley Gauge Figure 5.

6 Page 6 of Location (River Miles) Max Height (Ft) Width (Ft) Figure 6. GEO-TUBE PARAMETERS Notch Average Length of Pool Width Height Behind Geotube (Ft) (Ft) (Miles) Storage of Geotube (D-S-F) Table.

7 Page 7 of GEOTUBE AT RM 0.48 GEOTUBE AT RM.98 RS = 0.48 IS RS =.98 IS Ground 69 Ground 68 Bank Sta 68 Bank Sta Elevation (ft) Elevation (ft) Station (ft) Station (ft) Figure 7. Figure 8. GEOTUBE AT RM 5.0 GEOTUBE AT RM 8.7 RS = 5.0 IS RS = 8.7 IS Ground 659 Ground 648 Bank Sta 658 Bank Sta Elevation (ft) Elevation (ft) Station (ft) Station (ft) Figure 9. Figure 0. GEOTUBE AT RM RS =.05 IS Ground Bank Sta Elevation (ft) Station (ft) Figure.

8 Page 8 of HEC-RAS CALIBRATION Two historical river conditions which reflect different hydrologic conditions were used to calibrate the HEC-RAS model for the fourteen mile stretch of the Tallapoosa River. One period is a week in late August of 000. This period reflects extremely dry conditions. The second period is a week of this past September of 003 which contained many varying conditions: Weekend pulse operations, peaking power operation, system operational needs operation, and two days of irregular operations of differing pulse releases to facilitate the survey work of the Tallapoosa River. Figures and 3 illustrate the releases from R L Harris for the two separate week periods. Figures 4 through 7 illustrate how the HEC-RAS model for both periods compare with observed data at Wadley. From these results, it is viewed that the HEC-RAS model replicated historical flows and elevations at Wadley for a wide range of flow conditions which facilitates the evaluation of geo-tubes in place and how these geo-tubes may alter stage and flow conditions under vastly different conditions. R L HARRIS GENERATION SCHEDULE R L HARRIS GENERATION SCHEDULE 8/5/000 FRIDAY 753 CFS 9/6/003 SATURDAY 48 CFS 8/6/000 SATURDAY 70 CFS 9/7/003 SUNDAY 09 CFS 8/7/000 SUNDAY 0 CFS 9/8/003 MONDAY,3 CFS 8/8/000 MONDAY 33 CFS 9/9/003 TUESDAY,96 CFS 8/9/000 TUESDAY 40 CFS 9/0/003 WEDNESDAY,653 CFS 8/30/000 WEDNESDAY 8 CFS 9//003 THURSDAY,3 CFS 8/3/000 THURSDAY 53 CFS 9//003 FRIDAY,04 CFS 9//000 FRIDAY 49 CFS 9/3/003 SATURDAY,46 CFS Figure. Figure 3.

9 Page 9 of 607 Plan: USS AUG00 EX River: Tallapoosa River Reach: Harris to W adley RS: 0.00 Stage Obs Stage 606 Stage (ft) Aug000 0Sep000 Figure Plan: USS AUG00 EX River: Tallapoosa River Reach: Harris to W adley RS: 0.00 Flow Obs Flow Obs Flow Missing Data 4000 Flow (cfs) Aug000 0Sep000 Figure 5.

10 Page 0 of 60 Plan: USS SEP03 EX River: Tallapoosa River Reach: Harris to W adley RS: 0.00 Stage Obs Stage Stage (ft) //003 Figure Plan: USS SEP03 EX River: Tallapoosa River Reach: Harris to W adley RS: 0.00 Flow Obs Flow Flow (cfs) //003 Figure 7.

11 Page of RIVER CONDITIONS EVALUATED Several conditions were evaluated with either three or five geo-tubes in the river channel. First, an evaluation was made of the effectiveness of each geo-tube if that geo-tube was placed singularly in the river. Figure 8 illustrates the results for a dry channel condition with one unit best gate discharge (6,500 cfs) for one hour in a day. This evaluation showed that the geo-tube at RM5.0 has the greatest reregulation impact with the secondary geo-tubes at RM0.48 and RM.05 having the least impact GT RM 0.48 GT RM.99 GT RM 5.0 GT RM 8.7 GT RM Stage (ft) Jul55 0Jul55 03Jul55 Figure 8. Next, the same two periods used in calibrating the HEC-RAS model were used to examine either three or five geo-tubes. Figures 9 through illustrate how the stages and flow at Wadley would be impacted for these two time periods. The two secondary geo-tubes in these evaluations show marginal impact during the dry period in 000 and no discernible impact during the wetter period in 003. Two other flow scenarios were evaluated. One was with one unit best gate discharge (6,500 cfs) from R L Harris Dam for one hour with 50 cfs base flow and the second scenario was two units discharge (,800 cfs) for two hours, also with 50 cfs base flow. Figures 3 through 6 show the results of these evaluations which are similar to the conclusions for the two other time periods.

12 Page of Stage (ft) Aug000 0Sep000 Figure Flow (cfs) Aug000 0Sep000 Figure 0.

13 Page 3 of Stage (ft) //003 Figure Flow (cfs) //003 Figure.

14 Page 4 of Stage (ft) Jul55 04Jul55 Figure Flow (cfs) Jul55 04Jul55 Figure 4.

15 Page 5 of Stage (ft) Jul55 04Jul55 Figure Flow (cfs) Jul55 04Jul55 Figure 6.

16 Page 6 of Steady state flow conditions were also considered to determine how these geo-tubes may affect out of bank conditions. Steady state flows of one unit operation (6,500 cfs), two unit full gate operation (6,000 cfs) and the 00 year flood condition (65,000 cfs at R L Harris and 95,000 cfs at Wadley) were routed using the HEC-RAS model. Results as illustrated in Figure 7 show that neither one nor two unit operation with geo-tubes in place would cause out of bank conditions. Routing of the 00 year flood indicates that elevations upstream of geo-tube location RM5.0 would be increased. Further analysis of this site may change this, possibly if the site is moved slightly upstream Tallapoosa River Harris to Wadley 00YR 00 YR GEOTUBES 6K 6K GEOTUBES 6.5K 6.5K GEOTUBES Ground 660 Elevation (ft) Main Channel Distance (mi) Figure 7.

17 Page 7 of SPECIAL OPERATIONS From the R L Harris Project Release Proposal Outline submitted by the Alabama Department of Conservation in May of 003, several operational scenarios are proposed. These include recreational flows for weekends in October and restrictions of peaking power releases from R L Harris during a two week spawning window in the spring. The following discusses potential means to address these. RECREATIONAL FLOWS The proposal requests a minimum of 450 cfs for three day weekends (Friday through Sunday) during the month of October. Subsequent comments by the ADCNR reflect an interest in recreational flows for four weekends in either September or October. The following is one potential means of meeting this by scheduling certain releases from R L Harris with geo-tubes in the river channel. Figure 8 shows the minimum schedule of releases and Figures 9 and 30 illustrate stages and flows for the three day weekend at Wadley. A dry channel (50 cfs intervening flow) was assumed for this analysis. BOATABLE WEEKEND SCHEDULE THURSDAY 70 CFS FRIDAY 540 CFS SATURDAY 540 CFS SUNDAY 40 CFS Figure 8.

18 Page 8 of Stage (ft) Jul55 0Jul55 03Jul55 04Jul55 Figure Flow (cfs) Jul55 03Jul55 04Jul55 Figure 30.

19 Page 9 of SPAWNING WINDOW The proposal requests a two week window without peaking operations for a spawning window. Two scenarios were evaluated with thirty minute pulses at either eight or twelve hour intervals. Figures 3 and 3 show release schedules and Figures 33 through 36 show the resulting stages and flows at the Wadley Gauge. SPAWNING SCHEDULE SPAWNING SCHEDULE SUNDAY 70 CFS SUNDAY 40 CFS MONDAY 70 CFS MONDAY 40 CFS TUESDAY 70 CFS TUESDAY 40 CFS WEDNESDAY 70 CFS WEDNESDAY 40 CFS THURSDAY 70 CFS THURSDAY 40 CFS FRIDAY 70 CFS FRIDAY 40 CFS SATURDAY 70 CFS SATURDAY 40 CFS Figure 3. Figure 3

20 Page 0 of Stage (ft) Jul55 Figure Flow (cfs) Jul55 Figure 34.

21 Page of Stage (ft) Jul55 Figure Flow (cfs) Jul55 Figure 36.