KISSIMMEE BASIN WATERSHED HYDROLOGIC ASSESSMENT,
MODELING AND OPERATIONS PLANNING
Request for Additional Information
Dear Model Presenter:
The following questions have been formulated based on discussions within the model
evaluation and selection panel for this project. We ask that you provide a response to
these questions in written form to Fernando Miralles-Wilhelm (email@example.com)
by 5 pm EST on Monday April 18th, 2005.
You are encouraged to provide as much detail as you feel is appropriate, as well as to
include graphics in your responses. To the extent possible, we request that you
support your responses with experiences based on specific modeling projects you
have already completed.
We appreciate your efforts and look forward to your written response.
List of Questions:
(1) The selected watershed modeling tool must have the ability to export, to ASCII
output, all time series data for each element at all locations within the model.
Please discuss the ability of your modeling tool to export these data.
(2) The SFWMD has invested a great deal of effort collecting discharge data for
each water control unit within the KB. These data will be available during
calibration/verification efforts. Describe how the model can utilize these data to
evaluate the performance of the simulation for each water control unit within
(3) Please describe the ability of the hydrodynamic equations within your tool to
address depth-varying roughness for overland and channel flow.
(4) Please describe the ability of your model to handle the flood event routing
issues in the four primary flow regimes described in Attachment 1. Your
description should include flow charts and graphics demonstrating how the tool
does or will address these conditions.
(5) Please provide an itemized list of calculation options for simulation of
infiltration, and a brief narrative explaining each of the algorithm options. In
particular, we would like to understand what simplifying options are available.
(6) Application and development of the modeling tool will require support from the
provider. Please describe your commitment and ability to make a specific
personnel assignments throughout the execution of this project including short
term, high intensity periods.
(7) During the calibration period of the model, there are significant structural
changes such as backfilling canals, removal of water control structures and
changes of water control operations. How can your model efficiently simulate
these changes within a simulation?
(8) Critical to the implementation of the model is the ability of the model to
properly simulate the control features of the water control structures. Typical
control features include:
a. The ability to include seasonal variation in regulation schedules
b. To limit maximum gate openings based on upstream and downstream
c. To simulate opening and closing rates of vertical lift gates,
d. The ability to hedge on structure discharge to meet recession rates on
down stream reaches.
Please discuss the ability of your model to effectively address these features.
(9) Our evaluation board is interested in how your model approaches the modeling
of seasonally-flooded wetlands and sinkholes fully contained within a model
cell Please provide a narrative statement explaining how these two features,
commonly found in some areas of the KB, would be simulated by your model.
(10) Please provide a detailed explanation of how supplemental agricultural
irrigation/crop water demands can be handled by your model Specifically,
please discuss the ability of your model to utilize an approach consistent with
AFSIRS (the SFWMD preferred crop demand tool).
(11) Please mention capabilities of your model with respect to the application of
water through rapid infiltration basins, drainage wells, and application of reuse
irrigation water and how it is separately accounted for in the water budget
(12) Please provide a description of the process used by your model to simplify the
simulation of field drains within each model cell, such as agricultural ditches
that are able to drain the water table to channels.
(13) It is expected that a significant part of the modeling effort will be spent in
optimizing the operations of complex structure rules applied to multiple water
control units in the KB. We anticipate optimizing numerous variables, for
multiple objectives, for approximately 15 water control units, individually and
as a system. This will be accomplished by performing screening model runs in
a decoupled mode (screening model optimization tool accesses output from
multiple watershed model runs) and in a coupled mode (where optimization tool
serves as a management simulation engine to the watershed model). The
optimization tool has not yet been selected. Please provide information on the
a. A description of how your modeling tool can be applied to or support the
screening functions described above.
b. If a third party optimization tool is selected, briefly describe the process
and time-frame to prepare linkages for the simulations described above.
c. If you have an optimization tool available, please describe it’s capabilities
to perform the simulations described above (provide examples).
d. The capability and feasibility to decouple the one-dimensional
hydrodynamic routing to be used separately for performance measure
(14) Please describe your model’s water quality modeling capabilities, particularly
for TMDL estimation and any experience with NPDES.
(15) Please discuss the ability of your hydrodynamic modeling tool to simulate dry
out or very low flows in the one-dimensional channels or two-dimensional grids
that may be encountered as part of the evaluation of performance measures
(16) Please provide a narrative of successful application of the model to similar
projects along with metrics on observed and simulated data from a completed
The Flood Routing Problem for the Kissimmee Basin
When modifications to water control operations within the Kissimmee Basin or other
physical alterations are considered, they must be evaluated for satisfactory performance
under flood event conditions. Flood event routings must be simulated in order to
determine if the modifications will satisfy strict flood protection levels of service
established in the basin. Below, the significant modeling issues and challenges to flood
event simulations in the Kissimmee Basin are summarized.
1. The reservoir routing problem: Upstream discharges must be kept within the limits of
what the downstream receiving water bodies can accept:
Upper Basin has a firm capacity of 3,000 cfs and a maximum capacity of 11,000 cfs—
this means that discharges from S-65 cannot exceed 3,000 cfs while the Lower
Kissimmee Basin is experiencing flooding, and can exceed 3,000 cfs up to a maximum of
11,000 cfs provided the S-65 discharge combined with local flows in the Lower
Kissimmee Basin do not cause flooding beyond prescribed levels.
To further explain how operations must be modeled to achieve this real-world objective,
consider the routing of a flood event through the Lower Kissimmee Basin. Local inflows
reach the river and floodplain at different points along the river and combine into one or
more flood waves along the river and floodplain. On top of this, if the Upper Kissimmee
Basin needs to make discharges, it has the right to discharge any amount up to the firm
capacity of 3,000 cfs. This flow is also added to the Lower Basin flows. These two
flows will result in flood stages along the river that may or may not exceed expected
flood stages for the magnitude of the flood event (Expected flood stages means: a five-
year event or one with a 20 % chance of annual occurrence should not exceed the “five-
year floodplain” that is established as part of the project lands; and the 100-year or the
1% event should not exceed the “hundred-year floodplain;” and so forth for all flood
events magnitudes.) Once the flooding in the Lower Kissimmee Basin falls below this
expected flood stage, the discharge from the Upper Basin can be increased above 3,000
cfs to a maximum of 11,000 cfs to fill the difference or “slack” that would otherwise be
experienced in the Lower Basin. The discharge from the Upper Basin cannot ever exceed
3,000 cfs if that discharge would occur in a way (at a time) that would cause stages
anywhere in the Lower Basin to exceed the expected flood stage.
Modeling flood events in this basin require that the Upper Basin/Lower Basin operations
in the simulation achieve the above balance.
Additionally, routing flood waters from pool to pool along a channel or from lake to lake
in the Upper Basin can be limited to the discharges physically possible based on the local
hydraulics or on discharges that satisfy the operational goals among the lakes and channel
reaches. Sometimes, when everything is flooded to excessive levels, full design
discharges may be made everywhere to the extent that local hydraulics will allow them.
However, when the flood event is subsiding, operational decisions will be interjected so
that a flooded area lying upstream of a more excessively flooded area may not discharge
at the full design level in order to allow the downstream area to recover from excessive
flood levels as quickly as possible, then both areas can return to normal levels as soon as
Modeling these channel and lake systems must simulate the operational decisions that
will reduce discharges as necessary when the system is recovering from the flood event.
2. The hydraulic routing problems at C&SF structures: The water control structures in
this basin are submerged ogee spillways topped with vertical lift gates and discharges are
generally significantly influenced by tailwater stages. There are a few structures that are
gated culverts which have low flow rates and in some cases serve as divide structures that
can be used to balance or fine-tune water levels, but are not significant in flood event
routings. These gated culverts are not the focus of this discussion. Modeling the
submerged ogee spillways require that simulations properly consider the structure
hydraulics and operational limitations that exist with these spillways.
Discharge at these spillways are always driven by a desired discharge that would satisfy
operational goals upstream or downstream of the spillway and/or within the broader
system of lakes and channels as described above. Desired discharge is met if physically
possible within the hydraulic limitations of the spillway. To determine the hydraulic
limitations of a spillway, the upstream and downstream water levels as well as the gate
opening must be known. The downstream water level will not vary much from one time
step to another if the structure discharges directly into a lake or large reservoir; however,
in the Kissimmee basin, usually, spillways discharge into a channel that is the connecting
link to the lake or reservoir. The tailwater in this channel is usually time varying and
requires that an unsteady flow approach be used to predict the tailwater for calculation of
the spillway discharge.
Additionally, the gate opening is restricted to a “maximum allowable gate opening”
which is based on not reaching erosive velocities in the channel downstream of the
structure apron. There is a unique maximum allowable gate opening for every
combination of headwater and tailwater. For most headwater and tailwater combinations,
the maximum allowable gate opening will require that the gate restrict the flow over the
ogee crest. For some headwater and tailwater combinations, the maximum allowable
gate opening will allow the gate to be raised fully out of the water where the structure
hydraulics are “uncontrolled.”
In the Kissimmee Basin, the low relief means that in most flow conditions, tailwater is a
factor in discharge. Tailwater stages with respect to headwater stages can be used to
classify structure hydraulics as “free,” “partially submerged,” or “highly submerged.”
Different discharges result from different degrees of submergence as a result of the
damping effect of the tailwater.
The combination of gate openings and tailwater submergence represent four primary flow
A. Controlled-Free: controlled flow (gates in water) with free discharge (tailwater
submergence is low)
B. Controlled-Submerged: controlled flow (gates in water) with submerged
discharge (the degree of tailwater submergence is a factor in discharge)
C. Uncontrolled-Free: uncontrolled flow (gates are clear of water surface) with
free discharge (tailwater submergence is low)
D. Uncontrolled-Submerged: uncontrolled flow (gates are clear of water surface)
with submerged discharge (the degree of tailwater submergence is a factor in
Again, for each time step in a flood event simulation, a model must assess the desired
discharge for operational goals, locally and across the basin and determine if the desired
discharge or what fraction can be achieved within the hydraulic limitations of the
spillway. The hydraulic limitations of the spillway are a function of headwater and
tailwater stages and a related maximum allowable gate opening. The tailwater stage must
be determined from the solution of the unsteady flow problem.