Table 1 shows the final results by each of the 37 quadrangles analyzed as part of this project. From 1992, the date of the NWI maps, and the latest date of available photography for the study area (mainly January of 1999, see Figure 2.5), a total of 512 acres of palustrine wetlands as mapped by NWI in the study area were shown to be destroyed by development, or 0.3% of the total.

Given the amount of new development we know to be occurring in the Houston area, the 0.3% figure seems to be extremely low. But several qualifications need to be made about this data.

First, the limitations in terms of dates of the available photography. Only 1995 photography was available for most of Chambers County. All of Harris County was limited to January of 1999 photography. The latest photography available for most of Galveston County was January 2000. We examined in greater detail the area around western League City, one of the fastest growing areas in the near-Bay environment.

Figure 6 shows the NWI wetlands on these quadrangles, and areas of current and proposed growth in a selected area of League City. Clearly much of the development in this area has been after January of 1999. It would appear that most of the growth in the Houston area in the study period occurred to the west of this study area. (Parenthetically, this fact might suggest that a narrow focus on the circum-Bay area may miss significant watershed damage which could impact Galveston Bay water quality as much or more than those areas immediately surrounding the Bay).

Secondly, there is the issue of the reliability of the NWI maps. When the NWI maps show the presence of wetlands, it is highly probably that the areas mapped are in fact wetlands, although some errors do occur. On the other hand, the error is much greater in terms of areas not shown as wetlands.

Figure 7 shows a detail of an area in western League City, an area of particularly intense development pressure. In the area labeled as “proposed development”, several dark circular and oblong areas are evident that are not mapped as NWI wetlands but that obviously are wetlands based on the geologic air photo signature of the prairie pothole - pimple mound complex. So not all of the wetlands are captured in the NWI mapping. Nonetheless, the NWI maps can be taken as a “sampling” of the total, and if that sampling was at least somewhat random, then our analysis of developed wetlands can also be taken as a reasonable sample. Thus, the 0.3% figure may not be all that inaccurate for the study area, but extreme caution should be used when discussing the acreage figures.

In terms of the timing, Figure 8 shows an area along Bay Area Boulevard in western League City. Much of the SE quadrant has now been developed. Preparation for development had already begun when the 1999 Lambert photo was taken, but the development signature was not pronounced enough to register development status with the analyst (this kind of interpretation error would add very little to the final numbers). In addition to the small wetland in the cleared area, the tract with the much larger wetland just to the south has already been developed or is in the process of development, as is much of the corridor along the newly opened Bay Area Blvd between FM 528 and FM 518.