Permeable pile groins are commonly used to protect eroding outer banks, but the spacing and resulting structure density controls interaction between adjacent structures and therefore influences local scour, deposition, and sediment transport. This study investigates the morphodynamic effects of two pile-groin spacing-density configurations using a distorted movable-bed physical model (horizontal 1:80, vertical 1:40) of a U-shaped reach representing the Kusan River, Indonesia. Each of the three cases; a no-groin case (Series 1), a 14.8 m spacing with 51 groins (Series 2) and a 29.6 m spacing with 26 groins (Series 3), were tested once at four prototype-scaled discharges (202.386–505.964 m3/s) for about 1 h without sediment feed. The model was calibrated under fixed-bed conditions (MAPE 1.17 % at 28 sections) and the tail-water level at Section 27 during the movable-bed runs agreed with the design relation (MAPE 4.53–5.00 %). The maximum prototype-scaled scour without groins in the main bend increased from 3.90 to 6.10 m with discharge. The 14.8 m/51-groin configuration limited it to 3.15-4.57 m and the 29.6 m/26-groin configuration to 3.00-5.06 m, the latter being lower only at the smallest discharge. Both layouts decreased the transport-stage parameter and moved many reaches from upper to lower or transition regime, most markedly for the 14.8 m/51-groin layout. The lowest RMSE for Series 1, 2 and 3 was given by Meyer-Peter and Müller (1948), Yang (1973) and Ackers and White (1973) among eleven empirical sediment-transport equations compared with the outlet-captured sediment. The results describe configuration dependent responses under the tested laboratory conditions and are limited by the 2:1 distortion, single runs, the short duration and the confounding of spacing with structure density.