---
title: "Tutorial 8 - Wet Weather Flows in Sanitary and Combined Systems"
canonical: "https://help.innovyze.com/space/xps/19661399/Tutorial%208%20-%20Wet%20Weather%20Flows%20in%20Sanitary%20and%20Combined%20Systems"
format: markdown
---
This tutorial describes the process for modeling sanitary flows and combined systems.
---
Sanitary sewers are designed to collect and convey sanitary flows. However, all systems collect additional flows to some degree. These flows include:
- Dry weather groundwater infiltration through leaks in pipes and manholes (pits)
- Additional infiltration during wet weather
- Inflow of runoff during wet weather
These components of the total hydrograph are shown in the following figure:
Numerous techniques are used to model these non-sanitary flows. A popular method is the Rainfall Dependent Inflow and Infiltration (RDII) unit hydrograph. RDII is modeled with three triangular hydrographs, each have three parameters:
| **R** | Fraction of rainfall that becomes runoff |
| --- | --- |
| **T** | Time to peak hydrograph, hours |
| **K** | Ratio of base time to peak time |
The procedure is also referred to as the RTK method. The three units and the total hydrographs are shown in the following figure:
Sewer models are calibrated using the mass balance described in equation (1). Dry weather flow is measured during dry conditions and is assumed to be constant (using the same hourly and/or daily variation patterns). Wet weather flow is calculated by subtracting dry weather flow from the total flow measured during storm events.
**Wet weather + Dry weather = Total flow (1)**
In the models, Runoff and Hydraulics modes are used to simulate wet and dry weather flows as per equation (2).
**Runoff + Hydraulics = Gauged flow (2)**
This exercise begins with a model that is calibrated for dry weather flows in Hydraulics. The RDII unit hydrograph method is used to simulate wet weather flow. The accuracy of the calibration is assessed against gauged data.
| **Level** | Novice |
| --- | --- |
| **Objectives** | - Use the RTK Unit Hydrograph method to model wet weather flow in a sanitary sewer
- Evaluate model flows relative to gauged data |
| **Time** | 1 hour |
| **Data files** | - **LWM01.xp** (starter model)
- **8CAM01.his** (gauged data for link 88650601.1)
- Wet weather flows.xlsx (spread used to analyze gauged data) |
In this tutorial, you will complete five models as shown below:
The first model (*LMW02.xp*) will be the dry weather flow model using only the **Hdr** mode. In this model, you will simulate the dry weather flow from residents and compare the result with the observed (gauged) data at the link **88650601.1**.
Using the model *LMW03.xp*, you will compare the flow during initial dry period with the gauged flow. You will use only the **Hdr** mode for this model as well.
In the model *LMW04.xp*, you will simulate the flow derived from rainfall (RDII) using only the **Rnf** mode. Note that you will only simulate the RDII in this model. This RDII will be transferred to the **Hdr** mode in the next two models for two different storm events. You will use the interface file option to transfer the RDII from the **Rnf** mode to the **Hdr** mode.
Using model *LMW05.xp*, you will simulate the dry weather flow + the RDII for the duration of Storm 1. Using *LMW06.xp*, you will simulate the dry weather flow + the RDII for the duration of Storm 2. You will compare both these simulated flows with the gauged data.
1. Launch the program:
1. At the opening dialog, navigate to the file *LWM01.xp**** ***and open it. Save the model as *LWM02.xp*.
2. Set the mode to Hydraulics (**Hdr**).
3. Double-click any black node and double-click **Dry Weather.**
> Macro (inline-media-image)
4. Select **Default DWF** and then click **Edit**. Note the **Dry Weather** loading. Click **OK** thrice to return to the network view.
> Macro (inline-media-image)
2. Add gauged data:
1. Locate link **88650601.1** (You may use the **Find Object** command from the **View **menu or alternatively press<**Ctrl>+F**).
2. Double-click to open the **Conduit Data** dialog.> Macro (inline-media-image)
3. Click **Gauged Data** and then click **Gauged Flow**.
> Macro (inline-media-image)
4. In the **Gauged Flow** dialog, click **Select File**. Navigate to the file *8CAM01.HIS**** ***and then click **Open**. > Macro (inline-media-image)
5. In the **File Format** section, check the **Raf-****Hydsys **(standard) radio button. Click **Edit** to view the data.
6. Alternatively, open the *8CAM01.HIS* file using any text editor. Refer to the help files to know more about the Hydsys file format. Note the flow data begins at 11:40 on 7 Sept 2013 and ends at 12:15 on 7 Oct 2013 (row 8648). Time steps are five minutes and flows are reported in m3/s. The total flow over the period was obtained by numerical integration of the record and is 14,469 m3. The information in the file can also be viewed by clicking **Edit** in the **Gauged Flow** dialog.
> Macro (inline-media-image)
7. Click the **Graph** button to view a plot.> Macro (inline-media-image)
8. Click **Close** and then click **OK** four times to return to the network view.
3. Determine the dry weather flows in the Hydraulics mode.
1. Go to **Configuration ****> Job Control > Hydraulics**. Enter the following settings:
2. In **Configuration > Interface Files**, uncheck all options.
> Macro (inline-media-image)
3. In **Configuration > Mode Properties**, only select **Hydraulics**.
> Macro (inline-media-image)
4. Solve the model by clicking the **Solve** tool > Macro (inline-media-image)
or pressing the **F5** key. The solution will require several minutes for completion.
5. Right-click link **88650601.1** and select **Review Results**.
6. Click the **Properties** tool from the **File **menu.
7. In the **Properties** dialog, under the **Show** section, select **Flow** and **Gauged Flow**. Clear all others and then click **OK**.
> Macro (inline-media-image)
8. With the cursor on the graph, right-click and select **Customization Dialog**.
9. In the **Style** tab, set the color to blue and the line style to dashed for **Flow**. Click **OK**.
> Macro (inline-media-image)
10. Draw a rectangle over the graph to zoom in on an area of the plot. Note where the gauged flow exceeds the model flow. Right-click and select **Undo Zoom** and re-zoom to review the graph. Close the **Review Results** window to return to the network view.
11. Open the output file. Examine Table E15 to find the total flow through link **88650601.1** (from node **88650601** to **88651702**) = 12,943 m3.
12. Save the model as *LMW03.xp* and rerun for the initial dry period (Sep 7 14:00 to Sep 10 12:10) and note the total flow in link **8865060.1**. The total flows are compared with the totals obtained by numerical integration of the gauged data (see *Wet weather flows.xlsx* from the downloaded **Getting Started Model Files**).
4. Add rainfall:
1. Save the model as *LMW04.xp*.
2. On the **Configuration** menu, select **Global Data**.
3. Select **Rainfall** as the database type in the left panel and **Measured Storm **in the right panel.
> Macro (inline-media-image)
4. Click **Edit**.
5. Click **Constant Time Interval**.
> Macro (inline-media-image)
6. Click **Graph **to display the data.
> Macro (inline-media-image)
7. Click **Close**.
8. Click **OK** three times to return to the network view.
5. Add the RDII record:
1. In the **Configuration** menu, select **Global Data**.
2. In the **Data Base Type** panel, select **(R) RDII** . Select **WWF **in the **Record Name**.
> Macro (inline-media-image)
3. Click **Edit**.
4. Select the box for **All Months**. Enter the data for the Short, Medium and Long Term Unit hydrographs as shown below.
> Macro (inline-media-image)
5. Click **OK** twice to return to the network view.
6. Enter subcatchment data:
1. Set the mode to runoff (**Rnf**).
2. Double-click node **86648902** to open the **Runoff Node** dialog.
3. For **Sub-catchment 1**, enter 1 for the **Area** , **Imp. (%)** , **Width** and **Slope** . Non zero values are required by the engine to complete the simulation. Even though non zero sub-catchment input parameters will generate small amounts of rainfall runoff, this runoff can be eliminated by using a sub-catchment infiltration record with high depression storage or initial losses.
4. Double-click the **Sub-catchments 1** button.
> Macro (inline-media-image)
5. In the **Sub-Catchment** dialog, double-click the **RDII** button.
6. Select **WWF** as the RDII global database record and set the **Use Defined Sewershed Area** to **10** ha. Click **OK**.
> Macro (inline-media-image)
7. In the **Sub-Catchment** dialog, set the **Rainfall** to **Measured Storm** and **Infiltration** to **Typical**. Note that the **Typical** infiltration record uses very high depression storage to remove the small rainfall runoff, which occurs due to the use of non zero subcatchment input data.
8. Click **OK** twice to return to the network view.
9. Enter the same sub-catchment data to node **88650601**, make sure the Defined Sewershed Area for this node is set to **20 ha**.
7. Set the Runoff Parameters:
1. In **Configuration > Interface Files**, select **Create New File in Runoff Layer**.
> Macro (inline-media-image)
2. In **Configuration > Job Control > Runoff > Time Control**, enter the following settings.
3. Also in the **Time Control** dialog, select **Use Simulation Start Time For Rainfall Event**.
> Macro (inline-media-image)
4. Click **OK** twice.
5. In **Configuration > Mode Properties**, under **Solve Mode**, select **Runoff **only. Click **OK**.> Macro (inline-media-image)
8. Solve the runoff. Solve the model by clicking the **Solve** tool or pressing the **F5** key. The solution will require several minutes.
9. Analyze the runoff results. Right-click node **88650601** and select **Review Results**. Click the **Properties** icon, and then select the **Rainfall** option as seen in the following:
> Macro (inline-media-image)
Note that there are two events over the simulation period. Storm 1 extended from Sept 10 14:35 to Sep 19 15:05. Storm 2 began Sept 23 18:30 and ended on Oct 3 2:45. If 12 hours are added to the end of the rainfall to allow RDII to drain though the network, then the two events will be examined for calibration.
> Macro (inline-media-image)
Table 2 shows the start and stop time for the rainfall and gauge data and the two events that will be used for calibration.
* *
*Table 2 – Times for Data Files and Calibration Events*
10. Simulate flows for calibration events:
1. Save model as *LMW05.xp*.
2. In the Job Control settings, set the start and stop time to the values listed in Table 2 for Storm 1. Set these for both the **Rnf** and **Hdr** mode time controls.
11. Determine the total flow in link** 88650601.1** from Table E15 and enter the value in Table 3. Examine the Review Results graph for link **88650601.1**.
12. Save the file as *LMW06.xp* and repeat for Storm 2.
*Table 3 –Wet Weather Flows for Storms 1 and 2.*
### **Questions**
1. Comment on the accuracy of the model in regards to sanitary flows. How could the calibration be improved?
FYI, adjusting the sewershed area for the RDII to say 200 ha at node **88650601** makes a better calibration by increasing the wet weather contribution.
2. Comment on the accuracy of the model in regards to wet weather flows. How could the calibration be improved?