I have an abstract class that defines a get, but not set, because as far as that abstract class is concerned, it needs only a get.
One possible answer would be to override the getter, and then to implement a separate setter method. If you don't want the property setter to be defined in the base, you don't have many other options.
public override double MyPop
{
    get { return _myPop; }
}
public void SetMyPop(double value)
{
    _myPop = value;
}