Subject: Why Groundwater outflow is a percent (%) and not a volumen of water? Posted: 12/4/2019 Viewed: 4058 times
We are developing a model in a very arid area, and in this study the relation between river and the aquifer is important. In this context, we find that the Groundwater Outflow is a percent and not a volume like groundwater inflow, and we like to ask why is the reason of this?.
Also, We like to ask if there is some way to change this and use a volumen for represent the flow from the aquifer to the river?.
Mr. Miroslav Kandera
Subject: Re: Why Groundwater outflow is a percent (%) and not a volumen of water? Posted: 12/16/2019 Viewed: 4008 times
Hello Mr. Ignacio,
first we need to make clear few facts:
1). you have groundwater node (aquifer) created
2). you have river created
3). you want to simulate direct relation between river and Groundwater (aquifer)
3). as runnof/infiltration link cannot begin at river and Transmission link cannot end at Groundwater, only way how to simulate direct connection (flow) from River to Groundwater is using Diversion.
4). In Diversion from River to GW (aquifer), you can specify exact amount of water flowing from River to GW by Maximum Diversion in CMS.
5). Direct connection (flow) from GW (aquifer) to river can be simulated using Transmission Link.
6). In Transmission Link from GW to River, you can specify Maximum Flow Volume with mˆ3 per second, where you can even specify volume and time step.
7). Natural Recharge, Storage Capacity, Initial Storage and Maximum Withdraval at Groundwater are all defined as specific volume.
8). If you want to simulate infiltration from Catchment to GW, you can create Runoff/Inflitration Link from Catchment to GW
9). In such connection, you need to specify Runoff fraction in percent share
10). It can be specified only if you simulate Catchment using Simplified coefficient method (Rainfall Runoff or Irrigation Demands only)
Now, conclusion and humble opinion if i may:
As you mentioned, you want to simulate relation between river and aquifer mainly. Then i would suggest, in case you want to simulate Catchments to use Soil moisture method (which require alot of data about catchment terrain and soil but can produce data about runoff and inflow to River/GW) or MABIA if want to do daily.
However, if area is arid enough, that rainfall can be negligible (i dont have experience with extremely arid areas, to say so) then focus only on connecting river and GW with mentioned Diversions and Transmission Links. That negligible rainfalls could be simulated via Catchment using simplyfied coefficient methdod, dividing outflow from Catchment to river and GW by some percent share you choose.
Yet, i dont have much experience with connection to MODFLOW, and how it affects whole simulation.
I would appriciate any suggestions that prove my opinions right or wrong.
Hope my suggestion help you somehow,
Faculty of Civil Engineering, STU Bratislava,Department of Land and Water Resources Management
Topic "Why Groundwater outflow is a percent (%) and not a volumen of water?"