WSPC01187

• File Number: 8283.200
• Description: Colorado River Basin-Colorado River Computer Models-Colorado River Decision Support System-Ray
• State: CO
• Water Division: 5
• Date: 12/1/1996
• Title: South Platte Water Rights Management System-Evaluation of SAMSON for Use in a South Platte Decision Support System
• Water Supply Pro - Doc Type: Report/Study

Section 3: Evaluation of SAMSON

The SAMSON model was developed as a tool to respond to the complexity of the interactions
between different components of the South Platte system (e.g., water rights, irrigation, pumping,
diversions, water reuse). It was supposed to provide daily management information as well as
guidance for long-term strategic planning on how to develop conjunctive use to the fullest extent
and how to recharge the aquifer.

The objective of the model, as stated by Morel-Seytoux and Restrepo (1988), was the evaluation
of basic state variables (e.g., groundwater table, reservoir water content) from which a variety of
other quantities may be derived. The program determines among other things: point flows in the
river at diversion points; flows at the Colorado-Nebraska state line; the amount of surface water
and groundwater available to "supply areas" (farm, city or industrial area; only farm is
implemented in the SAMSON model) and reservoirs; the evolution in time of the water table
during the simulation horizon; the amount of water recharged to the aquifer, the amount of
groundwater return flow to the river, and the amount of losses to the atmosphere through
evaporation and evapotranspiration.

SAMSON simulates a large-scale stream-aquifer system, the South Platte, and is used to evaluate
different management strategies for the South Platte River. The model has two components:
physical and allocation. It predicts the response of the system for each modification or different
water resource management strategies that are introduced into the simulated area. It can be used
to simulate the entire river basin system on a daily basis.

The primary limitations of the application of SAMSON are mainly due to the inadequacy of
available data, including the collection, data base storage, and retrieval of information necessary
for the model. It is difficult for the uninitiated user to understand and use it properly. The
extensive amount of information needed to run the program for a large-scale area such as the
South Platte makes the model configuration almost too big to be used.

The model is a "discrete kernel" model in that all hydrologic information is stored within a grid
area. Each grid cell is one square mile. The discrete kernel technique is used for modeling the
saturated groundwater zone. A program GENERA T generates all the discrete kernel coefficients
necessary to model an unconfined aquifer system. GENSAM, an acronym for the GENERA T
application, was created to be used with SAMSON. Using the coefficients obtained in program
GENSAM, SAMSON simulates the response of the aquifer system to any pattern of excitations.
In order to use the GENSAM program, the user is required to delineate the aquifer system,
superimpose and number a grid system, and gather and input all required data (Morel-Seytoux
and Restrepo, 1987).

SAMSON consists of two major components:

1. The decision or allocation model which distributes the surface and groundwaters in the
river basin for daily operations among the water users according to some specified rules of
operation. It deals with the decision processes of the agencies or individuals in charge of
operating the system. The water allocation model generates control variables that determine

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