REALM -- River, Estuary, and Land Model -- is a
project started and funded by the California Department of Water Resources
to develop a new model and decision support system for managing short-term
operations in the Sacramento-San Joaquin Delta and its tributaries, and
for planning long-term structural changes such as a Through-Delta Facility
or South Delta operational gates. We are working with strategic partners
such as Lawrence Berkeley National Laboratory and model-savvy GIS developers
so that REALM will be able to handle a broader set of practical problems
using high-performance numerical techniques tailor-fit to estuary, tide
and flooding applications.
Our initial product is a 2D model. We believe that accurate, adaptive
2D computation represents the most beneficial contribution to the current
range of delta simulation tools, balancing physical realism with the potential
for longer simulation. We intend to add optimized 1D modeling and adaptive
nested 3D computation in future releases for handling regions where the
flow characteristics are particularly stratified or channelized.
The Sacramento-San Joaquin Delta is experiencing
drastic declines in pelagic organisms, simultaneous with increased demand
for water from the Delta. Policy makers are asking the Bay-Delta engineering
and scientific community for answers to difficult hydrodynamic, water
quality, and biological questions which current computer models are not
able to provide in a timely or accurate manner. Furthermore, possible
catastrophic failures in the Delta, such as levee collapses and the interruption
of water supplies to the south, are difficult to analyze with existing
We believe the quality of modeling tools available should be commensurate
with the societal, economic, and environmental importance of the water
issues facing California. The scientific questions that confront us are
expanding to include difficult physics such as moving flood fronts and
evolving shorelines, greater scope and varied levels of required detail.
No single computational engine can be handle these requirements, but a
good technical design can envision the problems of the near future and
allow a compatible, efficient suite of tools for simulating estuary problems.
The REALM Project
REALM is motivated by two concerns:
- The need to improve model credibility and the
range of problems that models can solve, by increasing the accuracy
and speed of existing simulation models. Poor or unknown accuracy is
a barrier to model credibility, and speed limits the scope of problems
that can be analyzed.
- The need to significantly increase the usefulness
of models to policy-makers. Through interviews and our own experiences
in practical modeling, we have identified techniques that are critical
to continue solving the Department’s and California’s complex
and difficult water issues in the Delta, tributaries, and bays. We also
have collaborations to help develop systems tools such as a real-time
data assimilation system.
In order to achieve flexibility and accuracy over
a diverse range of problems, we emphasize two key techniques: adaptive
computation and embedded boundaries. Adaptive mesh refinement (AMR) is
a nested gridding technique that allows the model to concentrate computational
detail in regions that are difficult or interesting. Nested grids (an
even fraction of the coarser grid) might occur because of a flood front,
abrupt change in concentration or because of a user request for detail.
Embedded boundaries are a technique for representing complex or natural
domains such as a bay or channel within a rectangular Cartesian grid.
The advantage of embedded boundaries over other conforming methods such
as unstructured grids is that the boundary can evolve accurately in response
to tides or floods.
REALM will support better operational analysis
and decision-making with the following features:
- Real-time operation of the Delta using data
assimilation, a mathematical mechanism for integrating measured data
with an active model run. REALM’s statistical filters will allow
field data to be folded into the model as it becomes available, constantly
balancing model error and measurement noise and always maintaining a
modeling system that is “ready to go” using the best possible
depiction of current conditions.
- Policy-based management of the Delta using
model steering, where modeled values (water flow, depth, and quality)
are monitored, and gates or pumps operated adaptively according to operating
rules written by the decision maker. For instance, gates in the Delta
could be opened or closed when computed values of water quality or depth
reach pre-determined limits.