1. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 1

2. 2 O’Shaughnessy dam impounds O’Shaughnessy Reservoir for the city water supply. The Purposes of the Dams Delaware Dam impounds Delaware Lake for flood control. Both reservoirs also provide multiple recreational activities. The Delaware and O’Shaughnessy dams can alter the flow rates, to control levels downstream.

3. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 3 The United States Geological Survey (USGS) operates stream gauge stations at several points on the Scioto and Olentangy rivers. Most provide discharge readings in cubic feet per second (CFS). The Sources Station 03221000 below O’Shaughnessy Dam

4. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 4 The data from the gauges are available online. You can look back 1 to 120 days. You can select output as a graph or table. The Data Tabular output can be copied from the pages, and pasted into another application.

5. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 5 The copied data can be pasted into a spreadsheet. The spreadsheet can draw graphs from the data. This lets you create alternatives to the USGS graphs, with your own scale and timeframe. The Processing

6. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 6 You can enter data from more than one station into the spreadsheet. Then, you can create graphs that show multiple stations, in the same timeframe. The Processing

7. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 7 Over the 2010 Thanksgiving weekend, 2 - 3 inches of rain fell in the upper Scioto watershed. This image shows the rainfall totals for part of the timeframe shown in these charts. The Rain Event 9:00AM 11/24 - 8:00 AM 11/26

8. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 8 This station is the farthest upstream, in Delaware Co. The Scioto at Prospect The rate of rise is gradual, over the course of about 24 hours. It reaches its peak near hour 60. The flow rises from 27 CFS to 1,490 CFS. This part of the watershed received the most rainfall.

9. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 9 This station is immediately below the dam. It shows the rate of flow past the dam. The Scioto at O’Shaughnessy The dam is releasing less than 20 CFS until hour 50, then rises to 200 CFS by hour 65, then 978 CFS by hour 72. The reservoir behind the dam was very low before this rain event.

10. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 10 When there is such a large variation in readings, it can help to apply a logarithmic scale to the graph. This better shows the lower values. The Scioto at O’Shaughnessy The dam is releasing less than 20 CFS until hour 50, then rises to 200 CFS by hour 65, then 978 CFS by hour 72.

11. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 11 This is the river level below downtown, showing the effect of fast stormwater runoff from the city center. The Scioto at Jackson Pike Flow begins around 400 CFS, rising to 800 CFS, then to almost 3,000 CFS by hour 30. Then it declines until around hour 50, then rises again after hour 60. This part of the watershed received the least amount of rain in this event.

12. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 12 The river slowly rises at Prospect, filling the lake while the dam stays closed. The river spikes quickly and sharply downtown. Scioto Flow Overlay As the level stabilizes downtown, the dam begins to open. The dam is adding almost nothing to the flow for most of the timeframe.

13. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 13 Again, the gauge is immediately below the dam. The flow is held below 120 CFS, but rises to exactly 1,500 CFS between hour 32 and hour 48. At hour 65 it rises to almost 2,000 CFS. The Olentangy at Delaware

14. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 14 Here, the flow is uncontrolled. All of the impervious surfaces between the dam and I-270 add to it. Again, the numbers start around 120 CFS, but they change erratically. The Olentangy at Worthington The shape of the curve illustrates “fast rise, exponential decay” as the river surges and drains.

15. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 15 We see the dam holding back while the river fluctuates. Once the river begins to drop, the dam begins to open. The river is at 500 CFS, the dam opens to 1,500 CFS, and after a lag the total is 2,000 CFS. Olentangy Overlay While the dam flow shows steady lines, the river flow still shows gradual decay.

16. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 16 Now we see the dam opening in relation to the flow below town. The flow drops on both rivers until the dam opens, then there’s a lag before the increase shows at Worth- ington, and then at Jackson Pike. Scioto/Olentangy Overlay The second, smaller increase just begins to show at Worthington at the end of the timeframe.

17. Dam Control of Flow Rates on the Scioto and Olentangy Rivers 17 END