Multiple Reaches

[Nikki Trzcinski]

I'm trying to model a floodplain consisting of two reaches that combine into one. I have my topo all set up and ready to go. I understand about adding river reaches to a topo map, but how do I then combine those reaches into one?

Thanks,

Nikki Trzcinski

[Chris Maeder]

Nikki :

I guess that I would need more information to precisely answer your question. However, I will give it an educated guess.

If you have 2 streams flowing downstream and then combining into a single reach, then you can model this as a single river reach with a lateral side inflow for one of the tributaries.

To define the lateral inflow, select the cross-section upstream of the inflow as the active cross-section. Then, select Input | Profile Adjustment. The Profile Adjustment dialog box will allow you to define the new base flow (reduction in discharge), accounting for the loss of flow that enters the river downstream due to the lateral inflow. (The base profile flow is defined at the downstream boundary. Use Reach | Profile Description to see the initial base flow.)

If you need to move cross-sections from the upper river reach to the lower river reach, you can use commands contained in the Reach Manager to do that. Select the upper river reach as the active reach using Reach | Manager | Select Reach. Then, choose Reach | Manager | Reassign Cross-Section. The displayed dialog box will allow you to reassign the cross-sections from the upper river reach to the lower river reach. (Note that the upper reach cross-sections must be numbered in a such a fashion so that their IDs are greater than the lower reach cross-section IDs. Otherwise, the software will not know that they are upstream of the current reach.)

If you need to model the lateral tributary river reach, you will need to create a new river reach. Select Reach | Manager | Add Reach. You can then define the ID of the new reach. From then on, all cross-sections that you assign apply to this new reach. Similarly, all other input data that is assigned, only applies to this new reach. To switch between river reaches, again choose Reach | Manager | Select Reach.

I hope that this rambling has been able to give you some insight. If you have further questions, please see Chapter 3 of the RiverCAD / RMS User Manual for the section that discusses River Reaches. Also, you can post your inquiry on our forum or email me directly.

Sincerely,

Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com

Thank you Chris. That helps a lot. I will email you if I have further questions.

Nikki Trzcinski

Chris-

You had answered a question for me about a week ago concerning making two river reaches one. Thank you for your help.

I am now beginning my modeling and have a few questions. Let me be more detailed also. I am modeling a floodplain down a street. On one side of the street is a golf course that will be used to detain most of the current flooding. However, it was suggested to me that I model the golf course as one reach and the street as another and then combine the two reaches at the end of the golf course to complete the model. I am changing the effective model that I have to better represent the situation. The effective model used a blocked obstruction for the whole golf course, modeling the floodplain as just one reach. This was done
for a master plan and was on the conservative side. I need to better represent the fact that the golf course is not a blocked obstrction, but rather is lower than the road and will hold quite a bit of flow. (hence the need for a detention pond in the golf course).

How do you suggest I go about modeling this? I have two reaches of cross sections cut right now. The first contains just my Mulberry St. and then the wider cross sections after the golf course. My second reach consists of just the golf course cross sections. I did what you said for the main reach, and did a profile adjustment, but how do I connect the golf course reach to the main reach?? Or do I just look at the Golf Course reach as a separate model to analyze and analyze the main reach (Mulberry St.) with the profile adjustment, just like I have it now?

I hope I explained myself clearly. If not, let me know. Again, thank you so much. Know that your help is greatly appreciated.

Thanks,

Nikki Trzcinski

Dear Nikki :

You have it set up just right. Model the two seperate river reaches as seperate models, and simply treat the additional flow from the one of the reaches into the other reach as a flow adjustment.

If you have any additional questions or need any further information, please contact me again.

Sincerely,

Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com