Subject: Streamflow confusion Posted: 8/5/2014 Viewed: 9480 times
How does WEAP simulate streamflow? My understanding is that after one draws a River and specifies the headflow, WEAP essentially keeps track of withdrawals, gains, inflows, etc. Is there a way to have WEAP uniformly increase the stream flow instead of treating it constant across the whole segment or reach?
To clarify, suppose I draw a stream and specify the headflow as 10 CFS. By the time I reach downstream (right above the point where my stream flows in another stream) the flow (naturally) increases to 20 CFS. Suppose I want a flow requirement of 14 CFS right at the midpoint of the segment. Based on my understanding, according to WEAP this requirement is not met since after specifying the headflow the whole reach has a flow of 10 CFS in the absence of any withdrawals & deposits. However, I would like WEAP to treat the flow in the middle as 15. Is there a way to do this without breaking a reach into several smaller segments?
Yes you can have a semi-distributed modelling in WEAP. There are basically 2 ways to do this.
1. Keeping the same approach you have, ie you enters in WEAP the flow (e.g., 10 CFS for the headflow). After enterting this headflow, in the Data view, click on Supply and Resources > River and open the branches of your river. There you will see a sub-category Reaches where will be listed all the reaches between the nodes you have on your river. And you can specify Inflows and Outflows for each reache, so for instance you can pick up the reaches between the Headflow and your midpoint and enter a Surface Water Inflow of 5 CFS. And you do the same for the other reaches as you'd like. You can also specify some Evaporation, Groundwater Inflow and Outflow. Note that you can also model the Surface / Groundwater Interaction (cf. the section 'Groundwater - Surface Water Interactions' in the help menu menu of WEAP, more complicated). Please read the section Reaches in the help.
2. You do hydrological modelling based on climate date. This would be more realistic than entering a constant flow (e.g, 10 CFS for headflow). You have to use the Catchment object in WEAP (refer to the Catchment section of the help and the Hydrology section of the Tutorial). You can then add several catchment objects along the river to simulate contribution from sub-catchments and therefore create streamflow in a semi-distributed way.
Subject: Re: Streamflow confusion Posted: 8/6/2014 Viewed: 9422 times
Thanks for the help. I was thinking of a similar solution to (1) by adding artificial deposits, but by just changing the inflow in the reach it saves the clutter. In any case, the flow is constant along any one reach. Though I suppose by specifying other changes in the model it becomes less of an issue. (2) sounds interesting, but I don't have the data to pursue it and it still seems the flow would be constant between any two catchment objects along the river.
Devaraj de Condappa
Subject: Re: Streamflow confusion Posted: 8/6/2014 Viewed: 9416 times
Indeed, in any case the flow is constant within a reach: WEAP is not a distributed model. It's a pragmatical approach where what matters is the flow at some given location of the river, where we have water intake, dam/reservoir, hydropower plant etc.