Human modifications of natural streams in the name of habitat improvement take various forms, and the impacts of those improvements, both positive and negative, vary by orders of magnitude from stream to stream. The positive impacts are achieved through careful and timely planning, design, installation and monitoring of projects. Negative impacts are the results of rush jobs dictated by available money, a lack of consideration for limiting factors, untrained and inexperienced personnel, force‐fitting structures instead of bending the flow, lack of a watershed plan, poor communication and cooperation among disciplines, not using the team approach, and single habitat solutions which neglect diversity and artificial constraints. These problems are discussed from various perspectives, but emphasis on an integrated, bioengineering approach is threaded throughout the discussion of the problems and benefits associated with stream improvements and fish response. A general systems approach is presented which uses common language as a focal point for interdisciplinary communication, which is one of the major problems in resource management. Various conceptual models are discussed to describe system complexities, and factors which constrain project evaluation in terms of biological, physical, economic and other components. Conclusions about why some projects are successful, while others are not, are followed by recommendations for concerted and diversified efforts to improve our success in stream stewardship.

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On April 23,1980 Viking Orbiter One (VO-1), operating in the blowdown mode, completed a 10-s Mars orbit trim maneuver to position the spacecraft for its final science sequence in May-June 1980. This brings the number of propulsive maneuvers for VO-1 to 23. Total accumulated operating time for the rocket engine is 2896 s, representing a total impulse of 3.93 x 10 6 N-s. The estimated propellant remaining is sufficient to operate the rocket engine for an additional 30 s. VO-1 has completed more than 1700 days in space, 1400 days in orbit around Mars, and more than 2 yr of attitude-control-system operation with helium gas transferred from the propulsion-system pressurant tank. The mass of helium remaining is expected to be sufficient for attitude control through June 1980. This paper presents the flight history of the Viking 75 Orbiter propulsion systems and summarizes the design and test philosophy that have contributed to their success.

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