THE FLOODINGDRYING CYCLE IN RAINFED SEASONAL MEADOWS, CENTRAL CALIFORNIA

1
THE FLOODING-DRYING CYCLE IN RAIN-FED SEASONAL
MEADOWS, CENTRAL CALIFORNIA Hugo A. Loáiciga and
Allison L. Huang Department of Geography and
Donald Bren School of Environmental Science and
Management University of California, Santa
Barbara, CA 93106 USA
Introduction
Cumulative infiltration during phase 2 is
determined by solving an ordinary differential
equation which is based on Darcys law and water
balance. Time of initial ponding is used as the
initial condition. A similar procedure is used
for determination of infiltration during the 3rd
phase.
We developed a methodology for simulating ponding
and infiltration processes over a flat terrain,
where there is negligible overland drainage.
Infiltration and ponding dynamics, including
maximal ponding depth and duration of ponding,
are essential for flooding analysis in rain-fed
wetlands, the results of which can be used to
determine the feasibility of wetland restoration.
This methodology can also be used to quantify
ponding caused by irrigation.
Modeling with real rainfall data
The methodology described above assumes the
rainfall function is known. Of course, rainfall
in reality is not described by simple analytical
expressions. For simulation using real rainfall
data, the difference in methodology is that we
assume the rainfall rate to be constant in each
sampling interval, and we solve for cumulative
infiltration for each interval using the value at
the beginning of the interval as the initial
condition.
Methods
Simulations were run using both actual initial
moisture content and 80-porosity-equivalent
moisture content. The results for two soil types
are shown above.
General dynamics
The model is built on Green-and-Ampt infiltration
model, which the is physically based on Darcys
law. It assumes a piston-like infiltration
movement in a homogenous soil column and constant
soil-water tension at the interface.
Future research
This process is repeated until the end of
rainfall or the end of ponding, whichever comes
first.
We plan to examine the importance of antecedent
conditions on simulation outcomes. For instance,
to what extent do seasonal changes in parameter
values matter in predicting infiltration and
ponding? Furthermore, we would like to continue
our efforts on infiltration modeling using the
Horton infiltration model. We aim to assess the
relative suitability of Horton-based and
Green-and-Ampt based models for soils with
different hydraulic characteristics.
The modeling of ponding and infiltration is split
into three phases. During phase 1, the
infiltration rate equals the rainfall rate,
Results
Acknowledgement
We used the 100yr 24hr SCS Type I rainfall data
to simulate ponding and infiltration in Ojai
Meadows Preserve, located in Ventura County,
California. Soils samples were collected and
analyzed to obtain values for saturated hydraulic
conductivity, soil moisture, and porosity.
Values for soil-water tension were determined
utilizing particle size analysis (Rawls et al,
1996).
Funding for this project is provided in part by
the National Science Foundation IGERT grant
number 0114437.
and there is no ponding. Phase 2 starts with the
initiation of ponding and ends when rainfall
ceases or when ponding ceases, whichever comes
first. Phase 3 starts with the end of
rainfallprovided that ponded water is still
extantand ends with the extinction of ponding.
References
Green, W.H., and Ampt, G.A (1991) Studies on soil
physics, 1 the flow of air and water through
soils. Journal of Agricultural Sciences 4,
1-24. Horton, R.E. (1940) An approach toward a
physical interpretation of physical infiltration
capacity. Soil. Sci. Soc. Am. Proc. 5,
399-417. Rawl, W.J., Goldman, D., Van Mullen,
J.A., Ward, T.J. (1996). Infiltration. In
Hydrology Handbook, 75-124, American Society of
Civil Engineers, New York.