Subject: How is reach length defined? Posted: 5/4/2009 Viewed: 27014 times
I am not sure how the reach length is defined in WEAP. For example, a catchment A has a catchment node at its outlet which inflows as headwater into a defined river X using an runoff/ infiltration link which ends in a catchment inflow node Y. Therefore, when going to the REACHES section, it gives an option ' Below X headflow, then Below catchment inflow node Y.
As per my understanding, I have defined each sub-catchment as a wedge and approximately calculated the width of the wedge and the river length (basically the river edge of the wedge) in that particular sub catchment. So when coming to input the reach length, the options confuse me. What option exactly is the reach of the river X in the sub-catchment A?
I was hoping to attach the systematic view of my setup for clarity, but unfortunately cannot on the forum.
Subject: Re: How is reach length defined? Posted: 5/5/2009 Viewed: 27013 times
The "Reach Length" variable is only used to specify the length of a reach that is connected to a groundwater node, in cases where you want to model the groundwater/surface water flows by the head difference between the groundwater level and the river. If you do not want to model this GW/SW connection this way, you can ignore the reach length. (The alternative is to specify the GW/SW flows directly, or not at all.)
Therefore, if you are modeling the GW/SW flows by their head difference, enter for the reach length the horizontal length of interface between the river and groundwater node for each reach. In your example, because catchment A flows in at the river's headflow (at point Y), the length of the reach "Below X headflow" will always be zero. It would be better if WEAP did not show this reach, but you can just ignore it.