OCR Text |
Show The general consensus expressed in the SCCT is that the south arm of the lake is in the process of abnormal freshening, that the permeability or transmissivity of the northern railroad causeway is significantly less now than before the 1980s flooding period ( due to the addition of fill material and compaction) and that there has been a dramatic reduction if not cessation of return flow from north- to- south through the causeway structure. There are many points concerning lake dynamics and chemistry on which the state and some industry representatives agree, and some on which we may disagree. It depends on interpretation of a common database by different individuals and their individual assumptions. An important step to overcome these differences will be to agree on a common interpretation of the database being used. Once the USGS water- salt balance model is updated and is used to make some runs, questions about the validity and accuracy of the model will be answered. If the model tracks well, it can then be used with some confidence to follow changes in salt loads and salinities over changing lake levels, and make some estimates of the causeways permeability over time ( pre and post late- 1980s flooding). If the model does not track well, many of the present questions and points of disagreement that have been posed by industry representatives will remain. Additional work is needed to minimize the existing differences of opinion. When the USGS water salt balance model is completed, DNR engineers will utilize it to determine how salinity imbalance is occurring and what changes can be made to remediate the problem and the impacts to the GSL ecosystems. There are several possibilities to remediate the problem and sound data are needed to make the best decisions. The planning team is concerned that salinity trends are having a negative impact on the ecosystem. This planning effort provides an opportunity to change these trends and prevent further negative impacts. Storm winds cause seiches and can cause a buildup or pull down of the water elevation at either end of the lake and/ or against the causeway. These are short in duration, however. The head differential across the causeway, the differences in brine density, the area of the openings ( square feet) within structures such as the breach and the culverts and the overall permeability of the northern causeway ( whatever that may be) probably play a greater part in the movement of brines south- to- north and north- to- south than the short- term effect of seiching. Optimal biological productivity is hard to define and measure. However, biological productivity is a basic component providing for diversity and abundance of lake wildlife. Biologists recognize that meeting habitat needs of wildlife populations will help assure their sustainability. The biological productivity of the lake is important to provide for wildlife habitat needs. To restate the intent of A, maintain salinity within its historical range with the least impact on mineral extraction as possible. 289 |