This study was conducted to understand the variation characteristics of suspended solid in the Keum River Estuary. Water sampling was carried out regularly with response to the tidal cycle from September, 1986 to August, 1987. Analyzed or observed items were sea water temperature, salinity, TS, TDS, TSS, VSS, FSS. and also the relationships between wind velocity, precipitation, tidal cycle and TSS were investigated. It is found that the sea water temperature is the lowest in January(2.5℃)and the highest in August(24.4℃), and increases toward upstream in summer and vice versa in winter. Salinity is the lowest in August (13.6‰) and the highest in December(20.3‰), and the annual mean value shows 13.6‰. TS and TDS are firmly related with the variation of salinity, thus, high in spring and low in summer. The annual mean values of TSS in 199.8(65.3∼454.5)㎎/ℓ, highest in March 308.2(67.5∼792. 3)㎎/ℓ and lowest in June 36.8(10.9∼200.0)㎎/ℓ. The annual mean values of VSS is 22.0㎎/ℓ, its variation tendency is similar to that of TSS. The annual mean value of VSS /TSS ratio is 13.9(6.8∼20.2)%, which are not high level compared with those of polluted sea areas. This ratio is high in summer(24.1%) and low in autumn(13.3%), and increases toward the downstream direction. It is also revealed that TSS shows a positive correlation with the wind velocity(r=0.59), and a negative with the precipitation in the Keum River basin(r=-0.64). TSS concentration is primarily subjected to the tidal range and the freshwater discharge and also related to the resuspension of bottom sediments by the action of wind force or wind waves. The dilution rate is strongly subjected to the seasonal variation of the freshwater discharge, therefore, TSS concentration shows low in summer and high in winter. Under low discharge condition in spring, autumn and winter, TSS, VSS are high level in spring tide compared with those in neap tide : under high discharge condition in summer, these values are reversed that is, TSS is higher in neap tide than in spring tide.

To study the abundances of ichthyoplankton in the Nakdong River estuary, ichthyoplankton were sampled with standard net at approximately one month intervals from February, 1987 to January, 1988. Temperature and salinity in the study area showed large seasonal fluctuations due to the inflow of Nakdong River. Among 8 taxa of pelagic eggs occured in the study area, Sillago spp. occupied 37.3% of the total eggs; Coilia spp., 35.8%; Repomucenus spp., 13.7%; Engraulis japonica, 9.4%. These 4 taxa occupied 96.4% of the total eggs. Among 26 taxa of fish larvae, Engraulis japonica was the most abundant species and occupied 36.8% of the total larvae; Gobiidae, 15.3%; Repomucenus spp., 15.0%; Coilia spp., 14.0%; Hexagrammos otakii, 6.8%; Omobranchus elegans, 4.4%. These 6 taxa occupied 92.3% of the total larvae, The densities of pelagic eggs were more than 100 eggs/ 1,000m super(3) from May to October. The densities of larvae were 3.8~221.3 larvae/1,000m super(3). They were relatively high in May, July, and August.

The structure and change of the salinity front formed by the outflow of Keum River into the adjacent sea is investigated through the analysis of some possible data. The outflow of the river has no peculiar direction and controlled by the various factors. The analysis of data which are obtained at March and October show that at March, the salinity front is weakened as compared with October. The outflow pattern is not uniform but varies significantly with time period less than one week.

낙동강하구의 물리적 해황조사를 1986년 4월, 6월, 10월과 1987년 2월, 3월, 8월, 6회에 걸쳐 실시하고, 그 자료를 분석, 검토한 결과는 다음과 같다. 1. 음향측심에 의해 조사된 해저지형은 준설 또는 매립으로 인해 불규칙적인 요철이 생겼다. 2. 1986년에 관측된 결과에 의하면 동측수로에는 수류가 거의 없고 서측수로에 대부분의 유량이 흘렀기 때문에 낙조시의 최대속도는 1.5kt 정도였다. 3. 1987년 8월에 측정한 결과에 의하면 하구역에서의 흐름은 동측수로에서 약간 세게 나타날 정도였으나 서측수로에는 조석 때문에 약한 유동이 나타났다.

평균조차(平均潮差)가 10cm내외(內外)인 포항(浦項) 영일만(迎日灣)으로 유입(流入)하는 형산강(兄山江)의 감조구간(感潮區間)을 채택(採擇)하여 유역내(流域內)의 부조(扶助) 수문기준점(水文基準點)에서 관측(觀測)한 자료(資料)와 하천유량(河川流量) 및 수질측정자료(水質測定資料) 등을 근거(根據)로 밀도유현상(密度流現象)을 분석(分析)한 결과(結果)를 요약(要約)하면 다음과 같다. 1. 영일만(迎日灣)의 조석현상(潮汐現象)은 1일(日)1회조(回潮)이며 대조차(大潮差) 0.104m, 소조차(小潮差) 0.066m, 평균조차(平均潮差) 0.085m로써 해면(海面)의 변동(變動)은 매우 작았다. 2. 감조구간내(感潮區間內)에는 해수(海水)의 영향(影響)으로 인(因)하여 약(約) 270만(萬) 이상(以上)의 물이 저류(貯溜)되고 있으며 이중에서 염분농도(鹽分濃度)가 이하(以下)로써 관개용수(灌漑用水)로 이용(利用) 가능한 수량(水量)은 약(約) 120 만(萬)톤에 달(澾)하고 있다. 3. 해수침투현상(海水浸透現象)은 간만(干滿)의 차(差)에 의한 수위변화(水位變化)는 작으나 만조시(滿潮時) 염분침입(鹽分侵入)이 탁월(卓越)하여 뚜렷한 층(層)이 형성(形成)되는 성층밀도류(成層密度流)가 되고 간조시(干潮時)에는 염수(鹽水)쐐기가 후퇴(後退)하면서 쐐기 상류단(上流端)의 염분(鹽分)이 담수(淡水)와 혼합확산(混合擴散)되면서 유하(流下)하여 잘 혼합(混合)된 하구(河口)를 형성(形成)한다. 4. 염수(鹽水)쐐기의 길이는 5.9km로 계산(計算)되었으나 실제로는 4.4km지점(地點)에 설치(設値)된 연일(延日) 잠수교(潛水橋)의 영향(影響)으로 인(因)하여 동지점(同地點)에서 로써 염수(鹽水)의 침투(浸透)가 중단(中斷)된다. 5. 담수(淡水)와 해수(海水)사이에 어떠한 크기의 밀도차(密度差)가 존재(存在)하는 한(限) 수로(水路)바닥을 따라 흐르는 순상류(純上流) 방향(方向)의 흐름이 존재(存在)한다.