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A battle must now be fought. I did not know one was needed, but it is. Just because I retired is not the reason I can now begin or join others in the watershed battle. I am a slow learner. I have been too optimistic, too passive. Maybe there will not be a battle. I suspect there are too many papers written, too many departments and sections, too many agencies and programs to avoid the fire. The battle is one that must be waged to bring comprehensive total land management into the agency and to lay aside the watershed idea except as it applies to specific problems of water runoff and sediment movements ...and even then in moderation. A new age is upon us and the world can be seen as cells or pixels (not even polygons, except for map beauty), the units of the GIS maps. No longer must we aggregate and grossly deal with the watershed as the management unit or the analytical unit. The reasons why watersheds have been a part of conferences, and central to calls for improved land management, and pleas for conservation for a century has been that they do not work. People realized this and kept looking for solutions and quick fixes or more sincere work. There are too many problems with watersheds; there are too many idiosyncrasies, too many exceptions; too many political boundaries that over-ride the importance of ridge crests and valleys. They are a way of thinking and talking about water and rainfall and erosion, but just because watersheds have utility for that, they are not therefore all-purpose units for analysis, management, or policy for all natural resources and where people live.
Imagine a watershed. You are standing in a trout stream and looking up-stream. All around you is up. Behind you is down. The watershed is everything to the top of the ridge, then straight down to where you are standing. Where you stand is part of the watershed problem, the placement of the limits. The farther down the stream you work, the larger is the watershed (runoff, basin, and catchment...trivial distinctions of scale). The typical watershed feeds a stream. The atypical ones (rarely discussed in textbooks or elsewhere) are the smaller, triangular ones that are between the larger, often circular or elliptical ones, the ones that drain water across the surface directly into one side of a stream reach or main channel without it entering a channel. These are rarely measured, "gauged." In the typical watershed, the left side is usually very different from the right side. The slopes are different; the exposure of each slope to the sun is different. Wind velocities differ; precipitation differs. Evaporation near the top differs from that near the bottom. All is different! That is the greatness of these wonderful areas!
And what do we do? We act as if they are uniform. One area gives us so many cubic feet per second of flow. It spews out cubic meters of silt. Perhaps that is what is of interest to some but rarely to others. Once we had no computers and simplifying was needed. We had to take many numbers and develop statistics, simplistic summary numbers, to help improve descriptions and increase predictions. Now we have computers and we are still acting as if we did not.
I collect information for 30 factors for every 30 x 30-meter pixel in a watershed... for every pixel in an entire study area that includes 3 major watersheds and massive amounts of other area around them. I have the data! Why should I then assimilate and destroy and ignore the detail and effort and information that I have gained? Why should I use and discuss a generalized function about animals or plants within the border. That border is a function of where water falls (partially) and where some people (almost arbitrarily) decide to draw the line or limits at the lower areas (where exactly which direction water would run if it fell is often a guess). Standing in the trout stream, anyone can see that the left bank of the watershed is significantly different than the right bank! To assume away this difference when data are in hand is "playing in the sand box."
We can now estimate the temperature, precipitation, evaporation, and runoff from every unit (every 10-meter by 10-meter pixel) of a watershed or other land. Satellites show us what is in every pixel. We have abundant ancillary data. We can estimate the water leaving every pixel and entering every other pixel...and each is different because of roots, plants, slope, soil, bedrock, wind, etc. Once we had to generalize and knew we did so at great risk. Now we no longer have to.
Once watersheds were important to fisheries people. Soil losses were agricultural losses. Watersheds gained importance as a land use and analysis category. Perhaps they need to be retained by certain people and agencies. The time has come for the enormously complex problems of mining, recreational development, intensive forestry, manipulation of biodiversity indices, utility rights of way impact analyses, and land use development across political boundaries to use the pixel, not the watershed as the analytical unit. We must use what we have gained at such great costs; we must manage at the pixel level; we must load the landscape or broad-scale measures within each pixel; we must compute the costs of managerially changing each pixel and then the consequences of doing so. We need to continue to gather and refine the values for each pixel (about 300 major map layers) for relevant areas of responsibility and decision. We must not revert to "watershed management."
It hasn't worked; we have new data; we have new knowledge; we have the GIS. We need watershed boundary estimators, but those result in one map layer. We have to move past the over-generalizing concept of the watershed and think "pixel." Every spot of the Earth is unique and we have the new power to deal with those differences. To turn our personal or collective agency backs on this awareness is courting poor decision, mismanagement, and failure to protect the land and gain from it the potential benefits.
Watersheds also are very useful as communication tools - they can be understood by many publics and are
easily mapped. Caution should be exercised, however, when using watersheds to integrate wildlife management objectives into large-scale management plans. Because watersheds are defined by patterns of water drainage, their use as a management and planning tool for terrestrial species represents an artificial human construct that may not be applicable when addressing wildlife populations that range beyond the boundaries of a planning unit delineated by water
runoff.
The Wildlifer (The Wildlife Society), Issue No.299, April, 2000
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