Output:Time Series Maps

GSSHA can produce time-series maps of most spatially varied model output. In particular, GSSHA can write time series maps of spatially distributed rainfall, overland flow discharge, flow depths on the watershed, depths in the channel network, discharges in the channel network, cumulative infiltrated depth, infiltration rate, soil surface water content, groundwater head, contaminant concentration, volume of suspended sediment, maximum sediment flux, and net sediment flux. The project file cards required to write output time-series maps are listed in Section 3.11.3.

The MAP_TYPE project file card described in the above table determines the format of the output map. If the argument of MAP_TYPE is 0, then a series of GRASS ASCII maps are written, each with a different extension (e.g. depth.0, depth.1, depth.2 ...). These maps may be imported back into GRASS using the r.in.ascii command. Maps of types 1 and 2 are written in a generic WMS format. Maps of type 1 are written as ASCII files that may be read and processed by the user. All ASCII maps have the disadvantage of being up to twice the size of binary maps. Map type 3 is binary WMS format, which is the most compact, but cannot be directly read or edited. All maps are written every MAP_FREQ time steps.

Output time-series maps are very useful for obtaining an intuitive feel as to what is happening in the watershed at a given time. Using WMS to animate a series of maps provides the user with a moving time series of the output of concern. This allows the user to see how the variable’s spatial distribution progresses with time. Besides providing a means of visually analyzing the output, the output maps can be very helpful in spotting problems with the model. If fact, many years ago, the spatially varied maps of rainfall made obvious a problem in the inverse weighted distance rainfall distribution routine that may have otherwise gone by unnoticed.

In particular, the overland depth map is very useful for getting GSSHA to run properly. This map contains overland flow depths (m). If the INCLUDE_CHANNEL_DEPTH card is included, the channel depth (m) is written in place of the overland flow depth in grid cells that contain channel links. The first map always corresponds to the initial condition and shows the water surface profile corresponding to the base flow discharge within the channel network. Similarly, the last depth map corresponds to the end-of-simulation time, or to the time at which the program finished abnormally. Abnormal program termination caused by oscillating depths may show negative depths in the overland plane, typically in a checkerboard fashion. This map output can be very informative to illustrate the location of flow problems such as pits, dams, or flat regions in the overland flow plane.

After calibration of GSSHA, depth and discharge maps are useful for flood plain determination, flow velocity estimation, and a host of other purposes. The spatially-varied output maps of soil surface water content and cumulative infiltrated depth are useful for analyzing the spatial variability of infiltration, and may be used as input for other surficial process models. The spatially varied rainfall map is illustrative for demonstrating storm and rainfall dynamics. These maps can be imported into GRASS and displayed as a film loop using the GRASS xganim program. WMS can be used to animate the time series of maps and build standard AVI files that can be played back by any type of animation software. Such animations can make a lasting image when inserted into otherwise vanilla PowerPoint presentations.