Surface Water Source and Sink

This interface is used to input/specify surface water (lake, wetland, or reservoir) balance terms such as precipitation, evaporation, inflow from runoff, etc. This allows computing stage as an output from integrated aquifer-lake simulation (i.e., aquifer head and lake stage are solved simultaneously for each time-step of simulation).

SW Prescribed Source/Sink

This option is used to add a constant or time-dependent source or sink of water to the link (positive for source, negative for sink). For example, a source of water might be total inflow from a stream(s) or pumped water from a lake augmentation well. A sink of water might be the total amount of water pumped/extracted directly from the surface water body.

If the source/sink is time-dependent, select the 'Transient' option and click on the '...' (options) button to input transient data.

Runoff Flow Rate

This represents the contribution of overland flow into the surface water body. Users may specify a constant or time-dependent inflow rate, or it can be computed as: RO=P*C*A, where RO is runoff, P is precipitation (see below), C is the runoff coefficient, and A is the drainage area which is based on the lake area.

Precipitation

. This quantifies direct precipitation on to the surface water body. Users may specify a constant or time-dependent precipitation intensity (rate).

Evaporation Rate

This quantifies evaporation from the free surface of the water body. Users may specify a constant or time-dependent evaporation rate.

(Coming Soon) Check the box next to 'From Daily Evaporation' to upload or create a daily evaporation file. Check the box next to 'Import' and click the link to upload a previously created file.

Creating a Daily EVT file: First, specify the total evapotranspiration, EVT, during months of EVT - 'Total EVT from May to October'. (Note that users can specify a base EVT value for months outside of May to October. The total EVT is distributed over the months based on percentages specified under 'Percentage for May to October' (default of 18% for May, 20% for June, etc.).

Use the fields under 'Start Date' and 'End Date' to indicate the time period for creating daily EVT data.

Snow Melting Rate

In some environments, snow melt may play an important role in the long-term ('steady state') water balance or over a certain period of the year. Users may specify a constant or time-dependent evaporation rate

(Coming Soon) Check the box next to 'From Daily Snow Depth Data' to upload or create a daily snow melt file. Check the box next to 'Import' and click the link to upload a previously created file. Creating a Daily Snow depth file: Details coming soon!

Hydraulic Outlet Flow Rate

One or more outlets can be added to the surface water body using the outlet editing options. Outlets must be added/edited one-at-a-time.

First, click 'Add' to create a new Outlet. Then specify a Name (or use the default one that is assigned) and choose an outlet Type (stage-discharge relationship) for the outlet being added. The type of outlet determines the default values for sub options, e.g., Constant, Exponent, Cutoff Elevation, but these can be changed by the user. Fields that are disabled for a given outlet type are not used in the calculation. More details are provided in the following subsections.

Click 'Save Outlet' to finish the process. The number of outlets ('Numb Outlets') will be updated.

Use the drop-down menu next to 'Select Outlets' to select an existing outlet for further editing or deleting (click 'Delete' once the appropriate outlet is selected).

Rating Equation

This option uses a general stage-discharge relationship or rating curve (equation) to compute the outlet flow rate. The rating curve is of the form: Q=C(h-h₀)^m where Q is the discharge, C is a constant (discharge coefficient), h is the stage, h₀ is the cutoff (or cease to flow (CTF)) elevation, and m is a constant exponent with a values typically varying from 0.5 to 3.

Over flow

The flow over a spillway (or over flow) is calculated as: Q=CW(h-h₀)^m where Q is the discharge, C is a constant (discharge coefficient), W is the spillway width, h is the stage, h₀ is the cutoff (or cease to flow (CTF)) elevation, and m is 1.5.

Under Flow

Flow through an orifice (submerged opening through which water flows) is calculated as Q=CA(2g(h-h0)^m where Q is the discharge, C is a constant (discharge coefficient), A is the cross-sectional area of the orifice, g is gravitational acceleration (32.2 ft/sec), h is the stage, h₀ is the cutoff (or cease to flow (CTF)) elevation and m is 0.5.

Manning Equation

This option uses the channel characteristics directly at and after the outlet to calculate the outlet flow. Manning equation for open-channel flow is expressed as: Q=Ak/n(A/P)^2/3S^1/2 where A=W(h-h₀) is the flow area of the channel (W=channel width, h is stage, h₀ is cutoff elevation), k is a constant (1.0 for SI unites), n is manning roughness coefficient (which depends on surface channel properties), P is the wetted perimeter or the portion of the perimeter that is in contact with water, computed as 2(h-h₀)+W, and S is the channel slope.

Rectangular Weir

Flow over a rectangular weir is computed as Q=CW(h-h0)^m where Q is the discharge, C is the discharge coefficient (1.84 for SI units), W is the width of the weir, h is the stage, h₀ is the cutoff (or cease to flow (CTF)) elevation and m is 1.5.